Author Topic: Pax Instruments T400 thermocouple temperature datalogger  (Read 37853 times)

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Offline charlespaxTopic starter

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Pax Instruments T400 thermocouple temperature datalogger
« on: August 09, 2014, 09:40:07 pm »
Update: Right now you can purchase the T400 on Kickstarter

I'm super excited to share my project with you: the Pax Instruments T400 temperature datalogger. The Kickstarter campaign is launching in September.

The T400 simultaneously displays all four thermocouple temperatures, the ambient temperature, and a graph of the last 100 readings. It also saves the readings to a MicroSD card and prints the readings to the USB serial port.

 ;D I would be absolutely thrilled to get some feedback on the attached schematic. ;D I feel pretty confident with the design and I'm ready to have it scrutinized to bring it to the next level.

The main processor is the ATmega32U4 running at 8 MHz and 3.3V. The processor was chosen to give Arduino compatibility. Since it runs at 8 MHz and 3.3V it would be programmed as an Arduino Lilypad USB through the Arduino IDE.

The MCP3424 analog-to-digital converter measures the voltage produced by each thermocouple.

The MCP9800 temperature sensor is used for cold junction compensation.

The DS3231 real time clock is used to trigger readings. Between readings the device goes into low power sleep mode. The RTC wakes up the unit to take a reading, giving a longer battery life.

The T400 uses a standard BL-5C battery, great for battery replacement in the field.

As you can see in the attached screenshot, the device can display all four thermocouple temperatures while graphing the most recent 100 readings from all four channels. The graph can display each channel individually or all four together. If the ATmega32U4 has enough programming space, the T400 will also be able to display each channel in large numerals for easy viewing.

If you find this project interesting, learn more at Pax Insruments and sign up to be notified when the Kickstarter launches.
« Last Edit: September 12, 2014, 03:30:40 am by charlespax »
 

Offline penfold

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #1 on: August 10, 2014, 03:51:51 pm »
I like it.  The concept is good, assuming the price point for an assembled one comes under a reasonable figure, I think I could find a place for one on my bench.

A couple of comments though...

Do you have a reason for pulling one side of the thermocouple high and the other low? if you're just trying to give each input a defined voltage then you'd probably be better off just holding one side between a 1Meg potential divider and not feeding any current (no matter how small) through the thermocouple... if you're using it to detect whether there's a thermocouple present or not, i think i can let you off.

I'm a little apprehensive to see that there isn't any external gain provided for the thermocouple signals.  There's a lot of error thats likely to occur, if your getting descent resolution and accuracy in your tests i'll concede but you could make so much better use of that 18 bit resolution

I like the idea of a graph showing the last 100 or so samples, but it would be nice if to see a longer period down sampled yet having all the data on the sd card

 

Offline fcb

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #2 on: August 10, 2014, 05:55:04 pm »
The MCP3424 in 18 bit mode (3.75Hz sample rate!) gives an LSB of 15.625uV (PGA=1), type K thermocouple is approx. 39uV per degree C.

So whilst with PGA=8, you will have approx 0.05C per LSB, which is probably OK (although I think this is to close to a minimum resolution expected of 0.1C to be useful).  Also, you have a range of approx (PGA=8) 13,000C which is around 10 times more than the type K useful range - this seems like a poor match.

I would use the excellent MCP619 as a front end on each channel (perhaps with a gain of 20-40), and then a mux (4051) and then some more gain (jelly bean opamp perhaps) and use the ADC in your micro.  Or if you're not keen on redoing the work with the MCP3424, then at least add some gain from something like the MCP619 on the front of each channel, to give you a better match with the ADC.

Also, with a chunk more gain, you can have the option of using the PGA to set the range (0-1300C might not need better than 0.1C resolution, 0-100C could run at 0.01C resolution), or run at lower sample resolution for faster updates.

Incidentally, i have recently finished a design that uses a couple of MCP609's and a dsPIC for a four channel type K industrial control. The MCP609 as it was cheaper than MCP619 and met the spec I was after.  Each channel used two series gain blocks (g=24, g=10) as per the application example in the datasheet, however I only cared about positive temperatures. I also used the MCP9701A as the isothermal measurement.
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Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #3 on: August 24, 2014, 11:49:29 pm »
Thank you so much for your feedback, penfold!

Do you have a reason for pulling one side of the thermocouple high and the other low?... if you're using it to detect whether there's a thermocouple present or not, i think i can let you off.
Yes, this is for detecting if a thermocouple is connected. I basically took the whole thermocouple filtration and detection circuit from the Texas Instruments ADS1118 application report.

Quote from: Texas Instruments ADS1118 application report
The two 1-M? resistors (RPU and RPD) serve two purposes. First, these components offer a common-mode bias near midsupply. Connecting only one of the inputs to a common point decreases performance by converting common-mode noise into differential signal noise that is not strongly attenuated. The second purpose of these 1-M? resistors is to offer a weak pull-up and pull-down for sensor open detection. If a sensor is disconnected, the inputs to the ADC will extend to supply and ground and yield a full-scale readout that indicates a sensor disconnection.

I'm a little apprehensive to see that there isn't any external gain provided for the thermocouple signals.  There's a lot of error thats likely to occur, if your getting descent resolution and accuracy in your tests i'll concede but you could make so much better use of that 18 bit resolution
The MCP3424 has an internal PGA. I can boost the input up to eight times without any extra external components. Pretty sweet for minimizing the part count and keeping the board small.  :)  Do you think there would be any noise issues? From what I gather in the datasheet there shouldn't be any problems.

I like the idea of a graph showing the last 100 or so samples, but it would be nice if to see a longer period down sampled yet having all the data on the sd card
I totally agree and have added this to the list of possible features. Things are pretty tight with the ATmega32U4 programming space, so I hope we can squeeze it in. I've added your suggestions to the github repo: down-sample, plot from SD.

Did I cover everything?
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #4 on: August 25, 2014, 12:40:48 am »
Thank you, fcb. You've given me a few things to consider for the T400 and whatever the next device may be.

The MCP3424 in 18 bit mode (3.75Hz sample rate!) gives an LSB of 15.625uV (PGA=1), type K thermocouple is approx. 39uV per degree C.

So whilst with PGA=8, you will have approx 0.05C per LSB, which is probably OK (although I think this is to close to a minimum resolution expected of 0.1C to be useful).  Also, you have a range of approx (PGA=8) 13,000C which is around 10 times more than the type K useful range - this seems like a poor match.
I plan to have the T400 operate in 16-bit mode to get a 15 Hz sample rate. Loss in resolution, but an acceptable tradeoff to have the readings more quickly. The MCP3424 isn't necessarily the best system to use, but I started the design by leveraging other open source designs. I'm neither a programmer nor an electrical engineer, so there was some necessity to do this.

The full scale output range of the Type K thermocouple is about 62 mV. This provides 38 ?V/°C (= 62 mV/(1370 - -260)°C) of measurement resolution. In 16-bit mode the detectable signal level is 62.5 uV/PGA = 7.8125 mV (for PGA = 8 ). For the input signal level after a gain of eight, (38 ?V/°C) * 8 = 304 ?V/°C. The number of LSB/°C = (304 ?V/°C)/(62.5 uV) = 4.864 divisions per °C. This is mostly taken from the thermocouple example on  page thirty-four of the MCP3424 datasheet.

I can live with a 0.2 °C resolution for the ADC. I'm trying to get this out there for $150 or less.

I would use the excellent MCP619 as a front end on each channel (perhaps with a gain of 20-40), and then a mux (4051) and then some more gain (jelly bean opamp perhaps) and use the ADC in your micro.  Or if you're not keen on redoing the work with the MCP3424, then at least add some gain from something like the MCP619 on the front of each channel, to give you a better match with the ADC.

Also, with a chunk more gain, you can have the option of using the PGA to set the range (0-1300C might not need better than 0.1C resolution, 0-100C could run at 0.01C resolution), or run at lower sample resolution for faster updates.
I don't know if there's a right way to do it, but if there is, it probably sounds like that ;)  At this point in the design I won't be moving to using the microcontroller's ADC. However, I will consider adding some amplification to each channel if I can keep the added cost low enough. If the next device for Pax Instruments is a higher-end T400 type device, I'll definitely take the time and redesign like this.

Incidentally, i have recently finished a design that uses a couple of MCP609's and a dsPIC for a four channel type K industrial control. The MCP609 as it was cheaper than MCP619 and met the spec I was after.  Each channel used two series gain blocks (g=24, g=10) as per the application example in the datasheet, however I only cared about positive temperatures. I also used the MCP9701A as the isothermal measurement.
Sweet! Is that a design you can share? I'd love to see how the experts do it  :D  I'm using the MCP9800, which has an accurace of +/- 0.5 °C around room temperature.
 

Offline fcb

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #5 on: August 25, 2014, 11:28:56 am »
It was a design for a client - so I can't publish schematics etc.

You definitely want to be better than 0.2C, even if the accuracy isn't that good, it just feels better to have closer datapoints - and in this world of specmanship, why wouldn't you?  I would target 0.01C resolution to say 250C and 0.1C above that.

I don't think this will have a significant material implication to your price.  One other thing, I'd probably measure the isothermal block with a PT100/PT1000 RTD, as the MCP9700 series is not that accurate (although more than good enough for my application) - the least amount of calibration in production the better...


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Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #6 on: August 25, 2014, 01:43:11 pm »
You definitely want to be better than 0.2C, even if the accuracy isn't that good, it just feels better to have closer datapoints - and in this world of specmanship, why wouldn't you?  I would target 0.01C resolution to say 250C and 0.1C above that.

I don't think this will have a significant material implication to your price.  One other thing, I'd probably measure the isothermal block with a PT100/PT1000 RTD, as the MCP9700 series is not that accurate (although more than good enough for my application) - the least amount of calibration in production the better...
I'm pretty strapped for pins, so I'll look into a solution that uses an RTD with an i2c interface. This might even be a good opportunity to find a better ADC with an extra input I can use with the RTD.

Maybe switch from a single MCP3424 to two MCP3423 chips. Then I could run each in 18-bit mode and get 0.05 °C resolution. Not quote there, but it would keep software compatibility.

I'm going to dig around for some chip options. You're making some good points. Thank you  :D
 
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Offline mzzj

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #7 on: August 25, 2014, 02:48:54 pm »
I was projecting temperature logger around ltc2498 24bit 8/16 channel adc, arduino with sd card and some cheapo lcd display. Most of the code would be ready for arduino so even a programming noob like me should be able to get some results pretty fast.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #8 on: August 25, 2014, 03:08:50 pm »
I was projecting temperature logger around ltc2498 24bit 8/16 channel adc, arduino with sd card and some cheapo lcd display. Most of the code would be ready for arduino so even a programming noob like me should be able to get some results pretty fast.

The LTC2499 is basically the same, but with an i2c interface. Do you know if the 2°C absolute accuracy can be calibrated for to give better accuracy?
 

Offline mzzj

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #9 on: August 25, 2014, 03:40:37 pm »
I was projecting temperature logger around ltc2498 24bit 8/16 channel adc, arduino with sd card and some cheapo lcd display. Most of the code would be ready for arduino so even a programming noob like me should be able to get some results pretty fast.

The LTC2499 is basically the same, but with an i2c interface. Do you know if the 2°C absolute accuracy can be calibrated for to give better accuracy?
you can probably improve it by calibration. I was planning to use separate cold junction temperature sensor so haven't really paid attention For that.
I was thinking of pt1000 sensor or thermistor, probably bit easier to measure than pt100.
I think calibrated or binned thermistors were available with quite reasonable price.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #10 on: August 25, 2014, 04:07:16 pm »
you can probably improve it by calibration. I was planning to use separate cold junction temperature sensor so haven't really paid attention For that.
I was thinking of pt1000 sensor or thermistor, probably bit easier to measure than pt100.
I think calibrated or binned thermistors were available with quite reasonable price.
I only need four differential inputs for the thermocouples. And with eight differential inputs on the LTC2499 I can use another one for measuring the RTD circuit. Hmm, this is looking very appealing. I'd also get another three differential channels to play with.

Do you have a sense of the sample rate for the LTC2499/LTC2498? I'm looking through the datasheet and I can't find a specific answer.
 

Offline mzzj

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #11 on: August 25, 2014, 05:36:38 pm »
7 hz sample rate or with some trade-offs in accuracy you can get up to 15 sps.

ltc2498 offers pretty outstanding performance for thermocouple measurements:
I have the 1101A demo board for the 2498 and I can just throw 2 meter twisted pair cable (without any sort of input filtering components) to the connectors and LTC2498 will measure happily with less than 0.2 ppm or 1 uV rms noise! I see typically 1-2uV offset, ie practically nothing for thermocouples.


Input protection is one thing that you should think about. ESD protection would be the minimum and since thermocouples are often uninsulated from the tip its not that hard to stick one thermocouple to wrong place  with different voltage level than other channels.

 

Offline janekm

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #12 on: September 01, 2014, 10:11:59 am »
I've also sometimes looked at the kind of under-specced devices sold as these kinds of data loggers and thought someone should do better, so good job ;)

I like your power management circuitry, but I noticed that you currently use a 10k/30k resistor divider for measuring the battery voltage, which would drop >100uA with the device turned off... maybe either increase the resistances or stick a mosfet on the low side.
 

Online mikeselectricstuff

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #13 on: September 01, 2014, 10:34:40 am »
I've also sometimes looked at the kind of under-specced devices sold as these kinds of data loggers and thought someone should do better, so good job ;)

I like your power management circuitry, but I noticed that you currently use a 10k/30k resistor divider for measuring the battery voltage, which would drop >100uA with the device turned off... maybe either increase the resistances or stick a mosfet on the low side.
This is a better way to do it. (This is for 9/5V but the principle is the same)
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Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #14 on: September 01, 2014, 06:06:07 pm »
I like your power management circuitry, but I noticed that you currently use a 10k/30k resistor divider for measuring the battery voltage, which would drop >100uA with the device turned off... maybe either increase the resistances or stick a mosfet on the low side.
This is a better way to do it. (This is for 9/5V but the principle is the same)

Thank you mikeselectricstuff and janekm. I've opened this an an issue on github

I'm getting a total power draw in the off state of 0.16 mA, see github issue. I definitely want to reduce that and get rid of the ugly voltage divider hack.

I should be able to take this basic circuit and have the output of the 3.3V regulator enable the transistor. This way I can save a pin. The down side is when the device is in sleep mode; the transistor would still be passing current. I'll have to think about this a bit.
« Last Edit: September 01, 2014, 06:17:14 pm by charlespax »
 

Offline zapta

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #15 on: September 02, 2014, 12:16:03 am »
Very interesting, I am in the market for temperature logger to diagnose our central heating system.

Tree minor suggestions: use micro USB connector (more standard) and display with good contrast (in the pictures it looks like those greenish low contrast displays)
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #16 on: September 02, 2014, 12:30:57 am »
Very interesting, I am in the market for temperature logger to diagnose our central heating system.

Tree minor suggestions: use micro USB connector (more standard) and display with good contrast (in the pictures it looks like those greenish low contrast displays)
Thanks for your feedback, zapta. When I started this project I wasn't sure what use cases it would have. I've gotten a better picture now that I've put it out there on the internet.

The T400 already uses a MicroUSB connector and has through hole supports to make is strong. Github issue: https://github.com/PaxInstruments/t400-electronics/issues/55

I've switched to an LCD with a different backlight. The green was taken with an LCD while I was waiting for the manufacturer to to make a white version. It's a bit too bluish now, but it looks waaay better than the green backlight. I think it's pretty good contrast too (see attached). I've submitted a Github issue: https://github.com/PaxInstruments/t400-electronics/issues/57

 

Offline zapta

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #17 on: September 02, 2014, 01:53:08 am »
The T400 already uses a MicroUSB connector and has through hole supports to make is strong. Github issue: https://github.com/PaxInstruments/t400-electronics/issues/55

Perfect, many ignore the through hole support and the connectors peel off.

Have you consider having real time clock so the logs correlate with actual time/date?
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #18 on: September 02, 2014, 02:07:22 am »
Perfect, many ignore the through hole support and the connectors peel off.

Have you consider having real time clock so the logs correlate with actual time/date?
As soon as a connector popped off my prototype I implemented a solution. I just used the same part at the Blinky Tape. That's proven to be quite robust.

The T400 has an RTC. The interrupt mask triggers each reading then the T400 sets the next alarm and the device sleeps in between. The firmware can read the RTC date/time and prints it to the header of each new log file. However, the UI cannot set the date/time.

The ATmeag32U4 memory space is being stretched pretty thin. Programming in the functionality to set the RTC date/time isn't much space. Making the UI for the user to do it *does* take up a lot of space. I'll get the feature in there if I can. Even if I can't, having the RTC trigger readings is a must-have feature.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #19 on: September 02, 2014, 02:09:43 am »
Check out the electronics and firmware issues on GitHub. I think you might fine some inspiration for more ideas  :)
 

Offline zapta

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #20 on: September 02, 2014, 03:58:16 am »
[The ATmeag32U4 memory space is being stretched pretty thin. Programming in the functionality to set the RTC date/time isn't much space. Making the UI for the user to do it *does* take up a lot of space. I'll get the feature in there if I can. Even if I can't, having the RTC trigger readings is a must-have feature.

Between the u8glib, vprintf, sd and usb there is not much left of the 32K flash.  Having an open source project with low memory margin is not great but on the other hand the Arduino compatibility is a big plus IMO.

Some u8glib fonts require more memory than others, and possibly you make the existing fonts sparse, including only characters that you need (yak). There are other memory considerations with u8glib, for example drawing a rounded rectangle pulls the circle logic which adds ~800B IIRC.  If you need to speed up the drawing there are also tricks for that (you don't need to redraw the entire screen on each iteration of the picture loop, just that portion of the screen. BTW, the u8glib developer is very responsive on the Android/Display forum.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #21 on: September 02, 2014, 04:18:26 am »
Between the u8glib, vprintf, sd and usb there is not much left of the 32K flash.  Having an open source project with low memory margin is not great but on the other hand the Arduino compatibility is a big plus IMO.

Some u8glib fonts require more memory than others, and possibly you make the existing fonts sparse, including only characters that you need (yak). There are other memory considerations with u8glib, for example drawing a rounded rectangle pulls the circle logic which adds ~800B IIRC.  If you need to speed up the drawing there are also tricks for that (you don't need to redraw the entire screen on each iteration of the picture loop, just that portion of the screen. BTW, the u8glib developer is very responsive on the Android/Display forum.
Excellent points. We'll probably have to optomize the u8glib library or even switch to something else. We'll tackle that later if the space is really needed. Pairing down the font and limiting the device to only one font are musts! are musts!

Last week cibomahto implemented your speedup suggestion

Yes, the u8glib dev is great! I have asked for LCD support twice and both times was helped within an hour.

I've submitted you suggestions at github issues to track them. Thanks!  ;D
« Last Edit: September 02, 2014, 04:22:03 am by charlespax »
 

Offline zapta

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #22 on: September 02, 2014, 04:37:06 am »
... I just used the same part at the Blinky Tape. ...

I like that blinky tape. Just ordered one. Thanks for the pointer.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #23 on: September 02, 2014, 04:40:03 am »
... I just used the same part at the Blinky Tape. ...

I like that blinky tape. Just ordered one. Thanks for the pointer.
Sweet! Matt Mets made the Blinky Tape. He's also hacking on the firmware for the T400.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #24 on: September 02, 2014, 05:10:01 am »
This week I'm hacking onhardware version 0.8. Please keep the suggestions coming  :)
 

Offline zapta

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #25 on: September 02, 2014, 07:20:45 pm »
This badge may be a good fit for your product

http://arduino.cc/en/ArduinoAtHeart/HomePage

 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #26 on: September 02, 2014, 08:21:02 pm »
This badge may be a good fit for your product
I looked into the Arduino at Heart program. For now the Arduino Open-Source Community is the best fit.
 

Offline zapta

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #27 on: September 02, 2014, 08:44:23 pm »
I looked into the Arduino at Heart program. For now the Arduino Open-Source Community is the best fit.

I was not aware of it, will take a look. Thanks.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #28 on: September 02, 2014, 09:08:42 pm »
I looked into the Arduino at Heart program. For now the Arduino Open-Source Community is the best fit.

I was not aware of it, will take a look. Thanks.

Here are the programs:
Arduino AtHeart - The Arduino AtHeart program is designed for makers and companies wishing to make their products easily recognisable as based on the Arduino technology. The program is available for any product that includes a processor that is currently supported by the Arduino Development environment (see list below).

Arduino Certified - The Arduino Certified program is designed for companies using processors not currently supported by Arduino who want to certify a basic level of compatibility with the Arduino platform..

Arduino Community Logo - We want to foster the spirit of our mission giving communities and individuals the opportunity to continue organizing locally or globally, online or offline around Arduino, being recognizable as part of this amazing spontaneous community.
You can use the Arduino Community Logo to identify your local group, as it is or adding the name of your group.

"For more information about the "Arduino Certified" program please write to: certified [at] arduino.cc"

I requested certified [at] arduino.cc to review the Pax Instruments website. They asked me to add the trademark symbol and said it was good to go as you see on the page right now.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #29 on: September 04, 2014, 10:34:07 pm »
Pax Instruments is going to MakerFaire NYC to show off the T400. Come visit exhibit #42316 “Pax Instruments T400 Temperature Datalogger” and play with working prototype hardware. Who's going to MakerFaire?
 

Offline zapta

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #30 on: September 05, 2014, 11:47:01 pm »
Sweet! Matt Mets made the Blinky Tape. He's also hacking on the firmware for the T400.

It arrived today, will try to control it from a Python script.

BTW, I was surprised how short it is. Expected more for that price.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #31 on: September 11, 2014, 02:54:39 pm »
The T400 Kickstarter campaign is live!

It’s official! I’ve launched my first product for Pax Instruments on Kickstarter. You may have seen my post on Facebook or Twitter, but if you haven’t already, meet the T400 Temperature Datalogger.
 
The T400 can connect to four thermocouples simultaneously, and logs temperatures directly to an SD card, so it can operate independently or while connected to a computer.

I want to continue developing this product and expand the line to other instruments and I’d love your helping making it happen!

Here’s how you can help:

First, share the Kickstarter campaign on social media like Facebook and Twitter. Also contact any friends you think would be interested in the T400.

Second, if you can submit my project to the tip lines at sites you read, it’ll help my cause a lot. Tell them there’s a Kickstarter project you like trying to make Open Source lab instruments, so people with projects in mind don’t have to spend an arm and a leg.

Third, With a Kickstarter campaign, a lot of the success seems to come from attention at the very beginning. So it would be amazing if you could back this, at least for $1, and then share the campaign to your networks.

Thanks so much for helping me make this a reality.
 
Kickstarter campaign: https://www.kickstarter.com/projects/1880050573/pax-instruments-t400-temperature-datalogger

- Charles
 

Offline urlkrueger

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #32 on: September 18, 2014, 03:17:56 am »

Do you have provision for aging of the thermocouples?

I use type K tc's at 1200C and they definitely loose umph with age at these temperatures.  A method to provide a user adjustable offset for each tc would be a requirement in my book.

 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #33 on: September 18, 2014, 12:27:54 pm »
I use type K tc's at 1200C and they definitely loose umph with age at these temperatures.  A method to provide a user adjustable offset for each tc would be a requirement in my book.

That's a good idea. User configuration per thermocouple would be great. I've included your idea in the Calibration routine issue on Github.

What is involved in that calibration?
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #34 on: May 30, 2015, 09:03:42 am »
I just posted an update http://paxinstruments.com/t400-may-production-update/

Since our March update the T400 has moved steadily forward. The most challenging aspects of the T400 project appear to be behind us and the T400 schedule is now almost exclusively dictated by factory lead times. If everything goes smoothly, you should have your T400 some time in August, probably earlier.

Thermocouple connector

Creating the custom thermocouple connector has been the single biggest issue we have faced. We did a tremendous amount of testing on the handful of seemly suitable connectors out there only to find nothing would meet our needs. In the end we spent a lot of time and a lot of money making what is the world's first fully open source connector.

We believe this will be useful to other hackers, so you will be able to purchase the Pax Instruments surface mount thermocouple contacts in our store as soon as they become available. The precision metal stamping factory has our money and our designs. We should have samples for approval before June 15th.

Enclosure
The design is complete. SLA and CNC machined prototypes are approved. We are just waiting on the connectors, so we can confirm everything lines up before cutting a mold. The top panel that interfaces with the thermocouple connectors is dependent on the custom thermocouple connector and cannot be approved until we approve the connector. We talked to the factory about cutting all the part cavities except the top panel and cutting the top later. They said it would be more expensive and only save us a few days.

Silicone keypad

Because the enclosure design is so complete we decided to start production on the silicone keypads. You can take a look at the button specifications to get a sense of how they will look. We are shooting for black icons on a white smudge-resistant background.

Electronics
The schematic design is complete and the latest version of the board works as expected. We are making one more revision to swap out the prototype Keystone connector with our custom connector. This is a trivial change of the connector footprint.

To ensure the PCBAs and enclosure match properly the factory will fully assemble the T400s with enclosures. This will allow us to fix any unforeseen PCB mistakes should they arise. We will begin PCBA production as soon as we have the injection molded enclosures.

Firmware
The firmware is expected to be complete in time for MakerFaire Shenzhen June 19th. You can track the current milestone on Gihub.

New Products

We took a few days while waiting for prototypes to refine some of the tools we made while developing the T400 and released a few new products.

If you are interested in our LCD, but were not sure how to interface with it, we now offer the Pax Instruments Graphic LCD 132×64 Arduino Shield. The LCD shield incorporates the same pin swapping technology as the Arduino Configuration Shield.

We also stock a high quality, low cost K-Type thermocouple with winding handle. The connector is from Omega and sports a standard PTFE-coated K-type thermocouple.

We came across a few hundred ATmega1280-16AU chips for next to nothing and put them in the store. We're thinking about making a small run of some fun project for them. If you have an idea you'd like to share, please join us in the forum.

If you'd like to stay even more up-to-date and hear more from Pax Instruments, please like, follow, and share us on FacebookTwitter, and our blog. Thank you for your continued support :-)
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #35 on: April 06, 2016, 10:24:50 am »
We made it into the Adafruit store! This is a huge step. Thanks to all who supported us so far :-)

https://www.adafruit.com/products/3081
 

Offline PointyOintment

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #36 on: April 18, 2016, 07:39:14 am »
We made it into the Adafruit store! This is a huge step. Thanks to all who supported us so far :-)

https://www.adafruit.com/products/3081

Great news! I haven't been following the T400 closely—I didn't even know it had reached production—but I was just thinking the other day that I should buy one.
I refuse to use AD's LTspice or any other "free" software whose license agreement prohibits benchmarking it (which implies it's really bad) or publicly disclosing the existence of the agreement. Fortunately, I haven't agreed to that one, and those terms are public already.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #37 on: April 18, 2016, 05:53:39 pm »
Great news! I haven't been following the T400 closely—I didn't even know it had reached production—but I was just thinking the other day that I should buy one.

Thank you for checking out the project  :)   I shipped in back in February. So far the feedback has been positive. The only complaint has been that the MicroSD card can be difficult to remove with short fingernails. Totally my fault. Whoops!

The Adafruit store is out of stock, but should be back up soon. You can always get the T400 in my store. Or you could head to the github repo and make your own  :P

How do you plan on using your T400?
 

Offline Kean

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #38 on: April 19, 2016, 12:17:18 am »
Thanks for the reminder Charles, I've finally ordered one.

Also really glad to see you selling the custom enclosures and buttons by themselves.  I've ordered some to try out a design for some custom handheld instruments (light, fluorescense & spectrometry related and/or small current sources/loads for the bench).
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #39 on: April 19, 2016, 05:35:20 pm »
Well, that's exactly why I'm making them available :-)   I'd be happy to help if I can. Just let me know.
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #40 on: May 01, 2016, 04:35:29 am »
The T400 was featured on the Mailbag and got a thumbs up!  8)

 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #41 on: May 10, 2016, 04:48:26 pm »
If you're interested in influencing what might be the next device, please join the conversation at https://www.eevblog.com/forum/projects/pax-instruments-multilogger/
 

Offline charlespaxTopic starter

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #42 on: July 15, 2016, 09:59:33 am »
In the latest firmware in github gives 770 bytes available without removing any functionality via flags. If flags are used, a total of 9,570 bytes are available.

http://community.paxinstruments.com/t/customising-the-firmware-to-do-other-things/138/8
 

Online jpanhalt

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #43 on: April 26, 2023, 03:34:31 pm »
I realize this thread is old.  Charles Pax has kindly helped me out with finding a project box for my "Smart Roast" and asked that I post some pictures of how I repurposed the T400 box.  (See related thread here: edit:deleted link because of Chrome warning)  This project is/will be open source.  Code is MPASM.  I just have not had time yet to get that documentation cleaned up, but I will add it here.

My project used a PIC16F1789 and MAX31856 TC amplifier.  The rest is pretty standard support stuff.  I went with an Omega TC socket, and it was just a tiny bit too high to fit under the LCD that snaps into the board.  That was solved by making a slot in the board and effectively mounting it upside down on the bottom surface.  See attachment. 

The thing is, of course, a roast thermometer.  I added a clock for total time, a calculation of rate for internal temperature, and a calculation of finish time based on user input of desired final temperature.  With beef roast or pork and an oven temperature well above the target temperature (e.g., 325°F vs. 125°F/160°F) that rise in temperature was fairly linear shortly after internal temperature starts to rise.  I had noticed that linearity for years and used to do the calculation by hand.  I could never convince my children to keep such records, so I made this project for them.  I now like it too.

The case back panel is currently left open for access to the programming pins.  Once that is "done," it will be closed.  The other attachments are for the TC (type K) and battery charging/power (USB).  For the first prototype, I decided not to include on-board charging and have left the battery unattached.  Nevertheless, I have included a picture of the T400 battery compartment, which I really liked.

PCB back shows detail of how the TC socket is attached.
PCB w.LCD shows detail of how the LCD mounts to the PCB.
MAX31856  shows the top attachment of the TC socket.  I used cyanoacrylate adhesive to fixture the socket to the PCB strap on the backside.  It seems quite rugged.
PCB top is the whole board with the LCD flipped forward.
The final photos is just the PIC1789 for those who like to see the MCU.

I extend my sincere public thanks to Charles Pax.  Without the T400 case, getting this gadget to look so neat may not have happened.

Regards, John
« Last Edit: October 11, 2023, 01:56:38 pm by jpanhalt »
 

Online jpanhalt

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #44 on: May 08, 2023, 02:33:44 pm »
Penultimate SmartRoast Prototype (maybe)

I have mentioned my "SmartRoast" project in other threads.  At the suggestion of Charles Pax (see my previous post), I decided to post more detail here.  It's a roast thermometer that calculates a finish time from the user entered target temperature.  It does not predict temperature rise after removal from the oven.  The basic project was working within one Winter.  I then spent the next 4 years working on the graphical display, PCB, and perseverating about when to do my very first reflow soldering (done 2022).  Other projects were also done during that time.  My original PCB design included a BMS for a LiPo battery; however, that was deleted at the last minute as I became worried about heat and keeping the project simple for my first reflow attempt.  It runs on a 5V wall wart with a miniature USB plug. 

Changes anticipated or being considered for the next version: 1) On board BMS with a USB-C connector (definite); 2) Selection of meat type; 3) An initial calculation based on size and weight of the roast;  4) Change the MCU chip; 5) Change the TC amplifier and/or better noise filtering; and 6) Possible but less likely a change in the display.

Attached are the schematic and board design submitted to OshPark, Assembly code, some flowcharts that may help a reader find their way through the spaghetti "logic," and a link to the LCD that was used.

Comments:
1)  Coding is in Microchip Assembly and MPLab 8.92 tool suite.  It may not appear in text or assemble properly with the current assembler in MPLAB X IDE.
2)  RE: TC amplifier (MAX 31856).  That chip is sensitive to noise on the TC leads and can freeze up.  If that happens, turn device off, wait a few minutes, and restart.  I found that wrapping the TC leads through a ferrite filter/toroid helps.  The toroid is shown in some of the pictures.
3)  Flowcharts were done originally in draw.io which is now diagrams.net .  I continue to use the draw.io version.  The Histogram flowchart has not been updated in quite awhile and should be considered a rough draft.
4)  The LCD is not shown in the BOM.  It was obtained via AliExpress from Laurellcd.  It is described as: 13264 COG ST7567 lcd display graphic module SPI Serial 12pin FSTN gray with bright backlight serial module LG132643-FDW .  Note the FFC comes/came in 2 pitches.  The prototype has the narrower pitch.  The plastic legs snap into oval slots on the PCB
Link: edit link to avoid Chrome warning
User's Manual:
GUI
The switches are numbered top to bottom and left to right.  Upper left is SW1; lowest left is SW3.
During POR
SW1 = Run
SW2 = Menu select
SW3 = Power on/off
SW4 = Increase in Done temp
SW5 = Decrease in Done temp
SW6 = Inactive (not implemented)

During Run
SW1 = Clears screen and timer (settings unchanged from POR)
SW2 = Backlight on/off toggle
SW3 = Power on/off
SW4 = Command scroll up
SW5 = Command scroll down
SW6 = Inactive (not implemented)

Regards, John




« Last Edit: October 11, 2023, 01:57:41 pm by jpanhalt »
 

Offline Kean

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Re: Pax Instruments T400 thermocouple temperature datalogger
« Reply #45 on: June 19, 2023, 03:48:50 am »
I extend my sincere public thanks to Charles Pax.  Without the T400 case, getting this gadget to look so neat may not have happened.

Nice.

I bought a number of the T400 cases from Charles to build my own projects into as well.  Nothing I ever finished, but I still do use my Pax T400 datalogger.
 


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