Author Topic: miniLOG - Standalone Data Logger  (Read 12267 times)

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Offline fencluTopic starter

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miniLOG - Standalone Data Logger
« on: October 31, 2013, 06:41:35 pm »
I'd like to introduce my latest project. It's a standalone voltage logger that saves the logged data to an SD card. I call it the miniLOG, because it's small and well, it logs stuff...

I have just finished the PCB and am about to be ordering prototype PCBs. Hopefully it will be on the market by the end of the year.

More details on my blog:  http://timecircuits.blogspot.com/2013/10/minilog-precision-standalone-voltage.html

I'd love to hear your feedback, either good or bad. It's supposed to be a kind of public research to find out if anyone would be actually interested in it.



Peace.
« Last Edit: March 16, 2014, 10:31:25 am by fenclu »
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Offline DavidDLC

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Re: miniLOG - a precision standalone voltage logger
« Reply #1 on: October 31, 2013, 06:51:04 pm »
If there is no enclosure for it, then mounting holes to put some pcb standoffs would be good.
 

Offline tszaboo

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Re: miniLOG - a precision standalone voltage logger
« Reply #2 on: October 31, 2013, 07:01:27 pm »
dont put untented vias under a metal package (Y1). They might make a short.
 

Offline uoficowboy

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Re: miniLOG - a precision standalone voltage logger
« Reply #3 on: October 31, 2013, 07:07:41 pm »
Seems to be very similar in functionality to the logger products that Sparkfun makes... Not saying that makes it any less useful.
 

Offline fencluTopic starter

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Re: miniLOG - a precision standalone voltage logger
« Reply #4 on: October 31, 2013, 07:25:40 pm »
Holy crap, I haven't seen those before  :D
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Offline hagster

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Re: miniLOG - a Precision Standalone Voltage Logger
« Reply #5 on: October 31, 2013, 09:57:48 pm »
What's the fastest logging rate? Have you thought about oversampling to increase the bit depth?
 

Offline Alex

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Re: miniLOG - a Precision Standalone Voltage Logger
« Reply #6 on: October 31, 2013, 10:26:13 pm »
Hi fenclu,

Interesting project.

I am working on a setup for the study of metal deposition rate by sputtering. A logger similar to this would be very useful indeed.

The sort of intervals I'm dealing with are longer, say 1 week sampling period for a few years. Do you think miniLOG could be modified for such an application?

Another requirement is low noise, low drift, wide dynamic range etc, precision stuff. This is important as it can reduce the experiment time by months. So big plus if you can properly characterise it.

In academia multichannel acquisition = National Instruments which = $$$. But, a single, cost-effective, high performance channel is often what is needed!

Finally, such experiments are so long that a battery is not practical. Therefore there is a mains supply available, but special procedures are put in place in case of power failure. How will miniLOG handle loss of power? Will it resume sampling?

Maybe some of the above will hit a nerve with your design. As a suggestion consider differentiating miniLOG from the generic electronic dust from Sparkfun etc. Continuing the focus on precision would achieve this.

Alex
 

Offline fencluTopic starter

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Re: miniLOG - a Precision Standalone Voltage Logger
« Reply #7 on: October 31, 2013, 10:59:31 pm »
The project will probably be Arduino compatible so you can easily change the interval time to the desired value.

I have to note, the software is not ready, I haven't made all the decisions yet. If the board for some reason suddenly loses power all data to that time will be saved on SD card (the AVR should write to SD card in real time). At least I hope it's possible.

dont put untented vias under a metal package (Y1). They might make a short.

Got it, that via is now tented.

If there is no enclosure for it, then mounting holes to put some pcb standoffs would be good.

Sure, I'll get around to it tomorrow.
« Last Edit: October 31, 2013, 11:22:34 pm by fenclu »
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Offline Whales

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Re: miniLOG - a Precision Standalone Voltage Logger
« Reply #8 on: October 31, 2013, 11:59:41 pm »
I have had to setup environments around proprietary data loggers before.  Think of automating proprietary GUI java applications in Windows and you will have the right idea.

How I wish I knew about things like this back then.

Offline Alex

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Re: miniLOG - a Precision Standalone Voltage Logger
« Reply #9 on: November 01, 2013, 12:20:50 am »
I forgot to ask, is there any reason why you chose U4 to be THT?

Alex.
 

Offline fencluTopic starter

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Re: miniLOG - a Precision Standalone Voltage Logger
« Reply #10 on: November 01, 2013, 09:14:40 am »
I have had to setup environments around proprietary data loggers before.  Think of automating proprietary GUI java applications in Windows and you will have the right idea.

How I wish I knew about things like this back then.

Well, yeah but it's just an SD card logger. It does not have a USB connection (although I have put a serial connector on there if someone wanted to add bluetooth or USB to their board). After logging you will just get an SD card that plug into your computer and it acts as a mass storage. The logged data will be saved to a .txt file which you can then import to Excel or whatever you want.

I forgot to ask, is there any reason why you chose U4 to be THT?

Alex.


Yes, I'm using LM285 which is available in two packages - TO92 and SO8. TO92 meant smaller footprint and easier routing (+ less temperature drift if I remember correctly). It's a tight board, I'm actually having troubles putting holes on there.
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Offline fencluTopic starter

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Re: miniLOG - a Precision Standalone Voltage Logger
« Reply #11 on: November 06, 2013, 06:28:12 pm »
I converted one of the channels into a current logging channel by adding a 1ohm shunt resistor. So now I can't really call it a voltage logger. From now on it's a DATA LOGGER  :D
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Offline fencluTopic starter

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #12 on: November 24, 2013, 12:18:52 pm »
Here's an update on the miniLOG. I described the schematic on my blog: http://timecircuits.blogspot.com/2013/11/minilog-seires-part-2-circuit.html

I would be grateful if you could provide an outside opinion or possibly note any mistakes I've made in the schematic.

Also, I can't decide whether to use an SD card, or a microSD card, so please give me some advice on that.

miniLOG REV2 schematic (.pdf)
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Offline tszaboo

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #13 on: November 24, 2013, 06:21:41 pm »
Q1, D3 seems to be redundant. Do you need both of them?
 

Offline Maxlor

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #14 on: November 24, 2013, 11:40:59 pm »
I suggest that your serial interface should use the same pin layout as the commonly used "FTDI Cables", i.e. GND, CTS, VCC, TXD, RXD, RTS. If you don't have RTS/CTS, just leave those NC.

If it doesn't increase the size of the board, I'd pick an SD card slot. Those with MicroSD cards can use a dirt cheap adapter, and that way, both types of card work. Alternatively, just log to an eeprom and output the data over the serial interface?
 

Offline Harvs

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #15 on: November 24, 2013, 11:57:06 pm »
Just a comments on your schematic.  There's a lot of redundant stuff put on there, big labels, pretty pictures of random parts, but you haven't labeled some of the stuff that's actually going to be really useful when you're sitting at the bench with this thing and the schematic.  Stuff like the reference voltage, you've put a redundant comment below the voltage reference stating it's part number, when the part is already labeled, but you haven't put down what it's output voltage and tolerance is.  It means if I were building this, or debugging it, I'd have to go off and get the datasheet just to check if the reference was outputting the right voltage.

Many times on this forum people criticize connecting together a schematic with net labels, and yes I'm not a fan either.  But if you are going to, don't have vertical labels on connecting nets, they're 10x harder to find.  Also where reasonable, put inputs on the left and outputs on the right, it's just how most people read.  E.g. the connector for the ADC has no reason to be in a rotated orientation, you've got plenty of room on the page, so move some things around and place it on the left of the block with the net labels facing to the right.  Now it will automatically look like an input connector adjoining to those nets.  Now, even better, fix up those ADC input filters buy putting the grounds facing down (don't face grounds vertically), and arrange them such that you can connect it directly to the connector without using net labels.  This block would be much easier to understand and look a lot more professional.
 

Offline fencluTopic starter

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #16 on: November 25, 2013, 02:45:56 pm »
Like I said, it's still not a finished schematic. Thank though, I will tweak the little mistakes.

Q1, D3 seems to be redundant. Do you need both of them?

I guess I could get away without the D3, then I wouldn't have to deal with the dropout voltage of the diode.

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Offline fencluTopic starter

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #17 on: February 22, 2014, 08:05:19 pm »
I got my prototype PCBs. I started talking to my Atmega chip and developing the software. I do however have a problem with the DC-DC converter. As you may know I used an AA battery with MCP1624/MCP1640 converter to boost the voltage to ~3.6V. The efficiency didn't turn out as expected and the entire circuit is drawing about 54mW (according to my shit multimeter), not the expected 10mW. I'm thinking of just ditching the AA battery and using two CR2032s in parallel with some sort of protection diode. That would give me about 500mW in total. But the other problem is the diode dropout voltage, the voltage would be too low for the SD card...

Now something like a Li-Po battery would be nice but I think that might be a bit of an overkill. I would appreciate some help and suggestions.

Here are some photos of the prototype:



« Last Edit: February 22, 2014, 08:25:54 pm by fenclu »
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Offline sacherjj

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #18 on: February 22, 2014, 08:22:28 pm »
I'm thinking of just ditching the AA battery and using two CR2032s in parallel with some sort of protection diode. That would give me about 500mW in total. But the other problem is the diode dropout voltage, the voltage would be too low for the SD card...

Look at using a P-MOS as reverse voltage protection.  Can reduce considerably the voltage drop of using a diode.
 

Offline dannyf

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #19 on: February 22, 2014, 08:25:20 pm »
Using a N-ch can do the same, at a lower price.
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Offline fencluTopic starter

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #20 on: February 22, 2014, 09:06:19 pm »
I am actually using one, as shown on the schematic:



Turned out I got my footprint wrong. And even after soldering it correctly the current flows both ways, even without the battery...
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Offline dannyf

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #21 on: February 22, 2014, 09:11:57 pm »
Quote
I am actually using one

Q1? It is not wired right and it wastes considerable energy.

Quote
the current flows both ways

Q1's body diode.

IRF has an application on this. Google it.

You may also check some of the arduino's circuit to see how they switch between usb power and outside power supply: the issue here is similar.
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Offline dannyf

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #22 on: February 22, 2014, 09:18:43 pm »
The principle of the IRF appnote is very simple: use the body diode to conduct initially. Once the voltage over the load is sufficient to turn on the mosfet, you are in the linear region.
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Offline fencluTopic starter

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #23 on: February 22, 2014, 09:25:17 pm »
Ok then, I removed the Q1, shorted out the drain and the source and removed R3. It still uses 15mA...Could be my crappy meter...
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Online mariush

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Re: miniLOG - a Precision Standalone Data Logger
« Reply #24 on: February 23, 2014, 12:09:40 am »
Quote

If it doesn't increase the size of the board, I'd pick an SD card slot. Those with MicroSD cards can use a dirt cheap adapter, and that way, both types of card work. Alternatively, just log to an eeprom and output the data over the serial interface?

If you're going to use EEPROM, you might as well use something cooler (but a bit more expensive) like FeRAM.

For example, you could use this: http://uk.farnell.com/ramtron/fm33256b-g/fram-mpu-support-256k-14soic/dp/2103831

Datasheet here: http://www.cypress.com/?docID=42548

It's a 256 kbit feram with real time clock, alarm , event counter, works with 2.7-3.6v, 100 trillion writes, the works. Save money on separate rtc chip, lower power consumption because it uses less power than eeproms and it's fast (almost instant) etc etc.
« Last Edit: February 23, 2014, 12:13:18 am by mariush »
 


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