Poll

Which module do you like to see in PlainDAQ

ESP-WROOM-02 (Wi-Fi)
1 (50%)
HM-BT4502(A) (BLE)
0 (0%)
Show me the results
1 (50%)

Total Members Voted: 2

Voting closed: May 19, 2022, 07:24:53 pm

Author Topic: PlainDAQ - open source DAQ module for Raspberry Pi Pico  (Read 24317 times)

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Online Marco

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #50 on: August 16, 2022, 01:46:22 am »
A 220k series resistor can hold off mains voltage to the extent the opamp input protection diodes can conduct the current with the resistor burning less than 0.25W, though some external clamp diodes for the opamp still make sense (it's on the edge). With a 10nf parallel capacitor the resistor contributes noise up to around a 100 Hz and won't really be an issue give the ADC precision. R4 needs to go and the RC filter needs to be put behind the opamp.

About the opamp, why not something nice like say MCP6V69?
« Last Edit: August 16, 2022, 02:09:53 am by Marco »
 
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Offline palpurulTopic starter

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #51 on: August 16, 2022, 06:52:25 am »
A 220k series resistor can hold off mains voltage to the extent the opamp input protection diodes can conduct the current with the resistor burning less than 0.25W, though some external clamp diodes for the opamp still make sense (it's on the edge).

I get it now. with 10nF cap my bandwidth goes down to 450Hz my bandwidth is going to be around 100kHz.

With a 10nf parallel capacitor the resistor contributes noise up to around a 100 Hz and won't really be an issue give the ADC precision. R4 needs to go and the RC filter needs to be put behind the opamp.

Wouldn't resistor contribute to the noise of the overall system until the equivalent noise bandwdith of the input filter (220k, 10nF) which should be more than 450Hz.

About the opamp, why not something nice like say MCP6V69?
That's too expensive, I am trying make something affordable with jellybean parts.


 

Online Marco

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #52 on: August 16, 2022, 10:52:37 am »
I get it now. with 10nF cap my bandwidth goes down to 450Hz my bandwidth is going to be around 100kHz.
As I said, the RC filter has to be moved behind the opamp. The 10 nF capacitor would be across the 220k resistor, not across the opamp input. At high frequencies it forms a capacitive divider with the input capacitance of the opamp (almost unity).
« Last Edit: August 16, 2022, 11:16:39 am by Marco »
 
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Offline palpurulTopic starter

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #53 on: August 19, 2022, 09:19:44 am »
As I said, the RC filter has to be moved behind the opamp. The 10 nF capacitor would be across the 220k resistor, not across the opamp input. At high frequencies it forms a capacitive divider with the input capacitance of the opamp (almost unity).

Sorry for my late response,

Could you just refer to a schematic? I am just curious to learn about this technique of protection because it's probably something I am not familiar with :)
 

Offline palpurulTopic starter

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #54 on: August 25, 2022, 06:32:47 pm »
As raspberry pi pico W is out, there is really no reasons for me have a wi-fi module in PlainDAQ.

I am considering removing the Wi-Fi Module and adding new features.

Any thoughts?​
 

Offline SiliconWizard

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #55 on: August 25, 2022, 08:59:05 pm »
Unless your may want to use Bluetooth as well. As said, the Pico W doesn't support BT - only WiFi. If you don't care about that, sure.
Or unless 1/ you want your users to be able to use a plain Pico (not W) or 2/ you have found a WiFi module that would be cheaper than on the Pico W (meaning: your board including WiFi module + Pico would cost less than your board without WiFI + Pïco W). But good luck with that as RPi has found a pretty good deal here.
 
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Offline palpurulTopic starter

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #56 on: August 26, 2022, 06:55:34 am »
Unless your may want to use Bluetooth as well. As said, the Pico W doesn't support BT - only WiFi. If you don't care about that, sure.
Or unless 1/ you want your users to be able to use a plain Pico (not W) or 2/ you have found a WiFi module that would be cheaper than on the Pico W (meaning: your board including WiFi module + Pico would cost less than your board without WiFI + Pïco W). But good luck with that as RPi has found a pretty good deal here.

THere won't be a BLE module in PlainDAQ because I ran a poll quite a while ago and many people preffered the Wi-Fi module. Not many people want BLE module.

Here is the poll: https://www.reddit.com/r/hwstartups/comments/uivmrr/help_me_decide_which_wireless_module_to_use_in/

Pico W costs extra 2$, I don't think I can find a module cheaper than 2$, so it make sense to remove wi-fi module and add new features. Maybe more storage (SDCard interface, PSRAM etc.) or variable supply voltage etc.
 

Offline PlainName

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #57 on: August 26, 2022, 11:46:45 am »
You were going to put the ESP-Wroom-32 in for WiFi, right? But that also does Bluetooth so you could just slap it in and have whatever anyone wants (both at the same time if it rocks your boat).
 
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Offline SiliconWizard

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #58 on: August 26, 2022, 10:49:43 pm »
Unless your may want to use Bluetooth as well. As said, the Pico W doesn't support BT - only WiFi. If you don't care about that, sure.
Or unless 1/ you want your users to be able to use a plain Pico (not W) or 2/ you have found a WiFi module that would be cheaper than on the Pico W (meaning: your board including WiFi module + Pico would cost less than your board without WiFI + Pïco W). But good luck with that as RPi has found a pretty good deal here.

THere won't be a BLE module in PlainDAQ because I ran a poll quite a while ago and many people preffered the Wi-Fi module. Not many people want BLE module.

Here is the poll: https://www.reddit.com/r/hwstartups/comments/uivmrr/help_me_decide_which_wireless_module_to_use_in/

Pico W costs extra 2$, I don't think I can find a module cheaper than 2$, so it make sense to remove wi-fi module and add new features. Maybe more storage (SDCard interface, PSRAM etc.) or variable supply voltage etc.

Actually yes you can. The ESP32-C3 chip is about $1. Count a few passives around this an a trace antenna on PCB, and done.
If you want something easier to integrate, the ESP32-C3-MINI (as a shielded module) is under $2.

The downside here is (would need to take a deeper look at the DS for the chip they used on the Pico W) is that I think the ESP32-C3 draws more current. If power consumption matters. (Which it probably doesn't if you are considering WiFi anyway...)
« Last Edit: August 26, 2022, 10:51:15 pm by SiliconWizard »
 
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Offline palpurulTopic starter

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #59 on: August 29, 2022, 02:10:37 pm »

Actually yes you can. The ESP32-C3 chip is about $1. Count a few passives around this an a trace antenna on PCB, and done.
If you want something easier to integrate, the ESP32-C3-MINI (as a shielded module) is under $2.

That actually makes a lot of sense  |O, but I've already made some progress with rp2040, so I don't really want to make that much change :-//. Besides that, I make use of PIO in RP2040 which makes data acquisition and waveform generation easier, so I kind of prioritize this over other options.

The downside here is (would need to take a deeper look at the DS for the chip they used on the Pico W) is that I think the ESP32-C3 draws more current. If power consumption matters. (Which it probably doesn't if you are considering WiFi anyway...)

You're right power consumption is not one of my concerns at the moment.
 

Offline palpurulTopic starter

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #60 on: August 29, 2022, 02:13:20 pm »
You were going to put the ESP-Wroom-32 in for WiFi, right?

Well yes, it was the plan in the past, but right now I've got some e-mails about removing the Wi-Fi module because people can use raspberry pico W for it.

But that also does Bluetooth so you could just slap it in and have whatever anyone wants (both at the same time if it rocks your boat).

There aren't that many people wanting to have bluetooth module on it really :(
 

Offline EsPiFF

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #61 on: October 29, 2022, 08:11:33 pm »
Quote
Actually yes you can. The ESP32-C3 chip is about $1. Count a few passives around this an a trace antenna on PCB, and done.

... after a 5 digit sum, to get your custom design certified, if you like to sell it. If you use a tm name like Bluetooth without a certification, to advertise it, the lawyers get after you.

When this project should show only technical possibilities, without an commercial background, for others to learn from or integrate the open source design into there solutions: then you don't need to think on safety or certification.

But when this project is intended to make a business from it (Crowd Supply) and/or should be used to teach and be used, for example by children, then safety standards REALLY should be implemented.

Here some hints:
  • your github repro does not contain schematics in PDF, but native KiCad files. That makes it difficult for people to help you, by looking over the schematics. The repro got updated last month, so my guess would be thats the latest HW version.
  • you should begin your design, by plan to fulfill safety regulations. Its not expensive, nor difficult, to design the product according safety regulations. This safes our children, and enables you to make money from selling products. I see, you spend much time with your own software, but over several PCB releases, still have unprotected inputs. I would make the device compatible with a standard like Sigrok, (or Labview, or GNU Radio, or Octave). They have all the features you will need years to implement by yourself. But that is your choice, you seem to have fun with it. But still: you need to implement at least the basic safety standards.
  • your inputs are connected, with a 100 Ohm resistor, to the DG611 multiplexer. More then + or - 18V will kill this IC. If 220V comes on the input, smoke comes out in best case, and a splitter of an exploded resistor fly to the eye of a bystander and he is blind. Somebody suggested a 220k resistor in series with every input, what is a good start. That is a good start. But keep in mind, that the resistor must withstand the high voltage. A standard 0603 resistor may be spec`ed for only 50V. So use ether a high volt resistor, or connect multiple resistors in series. Safety standards call for 1000V. I would add at least a pair of TVS diode after the 220k resistor, to clamp the voltage to save areas  for the DG611, +8V/-8V 
  • Input compensation: not required by law, but the 220k ask for compensation at higher frequencies. 10nF parallel to the 220k was suggested, but this depend on many factors, and should be measured for best results.

You should also improve your design, to not disappoint your backer. I doubt, that the current design in your github can reach the claimed Values.
  • It begins, before the signal even reach the terminals. You are talking about 450kHz bandwidth, but unshielded terminal inputs? Why no coax? BNC, SMA, or audio chinch? Not even balanced input. Even Audio with its max 20kHz, need shielded cable and ether coax connector, or balanced+shielded cables and connectors. Without this, you hardly get 8 bit. So use BNC or SMA connectors
  • Channel separation: you need ground between the inputs, or cross talk with ruin your 12 bit. With coax connectors, and a good layout, your can reach your planned specs.
  • Your power supply concept is unpractical for an 14 bit ADC. External 5 V from USB is noisy, and the switching regulator to generate the -5V add even more poison. You could use ether specific low noise switching regulator from Linear Technology(now ADI), but they are costly. Or use low noise linear regulators after the switching regulators. I often use the Richtek RT9193 series: they are ultra low noise, have a high PSRR not only at 100Hz, but also up to a few 100kHz, and still low cost. But they are only up to 4.75V available, and only positive. TI makes special ultra low noise linear regulator for positive and negative voltages, but they are not cheap. Also ADI and other make them. Just look in the datasheet for the PSRR over frequency plot. And of course, the output noise. The RT9193 has, for example, only 100 uV RMS noise.
  • Reference voltage: Why do you use a 4.096V reference, and then divide it by 2? And not use a 2.048V reference IC, like the LM4132AMF-2.0, or MAX6071AAUT21+T? The voltage divider have its own tolerances, temperature drift and will ruin your specs. 
  • AD8137WYCPZ-R7... why an 110MHz GBW, 450V/µs slew rate amp on this position? Such a beast needs extreme care to not oscillate, and is expensive. I would suggest you something like the MAX4462: It cost only 1/3th, has the same low Input voltage offset, easier to handle 2.5MHz GBW. But what ever op amp you use there, you should not supply it with the dirty USB-5V.  USB as power supply is good for digital things. To use it for analog parts with a high requirement on accuracy, you need to careful clean it up. Or galvanic isolate it. In your schematic is not a single ferrite bead, or common mode choke. Not even a linear regulator for the op amps. 
  • My advice: You have a working prototype, that is half of the product. Make a concept for safety according the regulations, and a concept for a clean power supply. You need minimum low noise RF linear regulators, separate analog and digital grounds, ether a star ground or galvanic isolation between the analog and digital parts. Specify the PSRR - over -frequency of each regulator, and each opamp. Also study the impedance graphs from different ferrite beads and common mode cokes, to see where they can help.
  • Even you like your own software solution: When you want this project to become a commercial success, or more attraction in the open source world: consider to add compatibility to standard software: the RP2040 supports tinyUSB, and tinyUSB support USBTMC.
    https://www.eevblog.com/forum/projects/usbtmcusb488-class-implementation-for-microcontrollers/
    https://k1.spdns.de/Develop/Projects/pico/pico-sdk/lib/tinyusb/examples/device/usbtmc/
    As beautiful your own software is: you will get 10x more attention, when backers can use Sigrok with your plainDAQ.
    Your users can then choose between your software and standard software.
     
  • If you want, that people help you: put PDF schematics on your github, then they can help you. Otherwise your on your own. 
 
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Offline palpurulTopic starter

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Re: PlainDAQ - open source DAQ module for Raspberry Pi Pico
« Reply #62 on: November 03, 2022, 01:02:04 pm »
Hello I am the guy building the PlainDAQ, unfourtunately I had to take a huge brek because my main job won't allow me to work on it :(

... after a 5 digit sum, to get your custom design certified, if you like to sell it. If you use a tm name like Bluetooth without a certification, to advertise it, the lawyers get after you.

PlainDAQ won't include any bluetooth and wifi capability I moved on from it because there is a version of pico with Wi-Fi already.

your github repro does not contain schematics in PDF, but native KiCad files. That makes it difficult for people to help you, by looking over the schematics. The repro got updated last month, so my guess would be thats the latest HW version.
I will upload it tomorrow. The hardware is not the latest I will have to make a few changes TBH.

you should begin your design, by plan to fulfill safety regulations. Its not expensive, nor difficult, to design the product according safety regulations. This safes our children, and enables you to make money from selling products. I see, you spend much time with your own software, but over several PCB releases, still have unprotected inputs. I would make the device compatible with a standard like Sigrok, (or Labview, or GNU Radio, or Octave). They have all the features you will need years to implement by yourself. But that is your choice, you seem to have fun with it. But still: you need to implement at least the basic safety standards.
Safety regulation issue is of the area that I am not really capable of, how should I get started to make something compliant. I haven't so much thought about making it compatible with already existing standarts, but it's a great idea, I was rushing to et something working, so I haven't had a chance to take a deep look into those issues.

your inputs are connected, with a 100 Ohm resistor, to the DG611 multiplexer. More then + or - 18V will kill this IC. If 220V comes on the input, smoke comes out in best case, and a splitter of an exploded resistor fly to the eye of a bystander and he is blind. Somebody suggested a 220k resistor in series with every input, what is a good start. That is a good start. But keep in mind, that the resistor must withstand the high voltage. A standard 0603 resistor may be spec`ed for only 50V. So use ether a high volt resistor, or connect multiple resistors in series. Safety standards call for 1000V. I would add at least a pair of TVS diode after the 220k resistor, to clamp the voltage to save areas  for the DG611, +8V/-8V
I will add proper input protection, noted. THe new version had inputs directly connected to the opamps not the multiplexers, I had to use cheaper multiplexers because of the price and they are 5V rated.

Even you like your own software solution: When you want this project to become a commercial success, or more attraction in the open source world: consider to add compatibility to standard software: the RP2040 supports tinyUSB, and tinyUSB support USBTMC.
https://www.eevblog.com/forum/projects/usbtmcusb488-class-implementation-for-microcontrollers/
https://k1.spdns.de/Develop/Projects/pico/pico-sdk/lib/tinyusb/examples/device/usbtmc/
As beautiful your own software is: you will get 10x more attention, when backers can use Sigrok with your plainDAQ.
Your users can then choose between your software and standard software.
That's a glden advice for me and I'd like to really thank you for this suggestion. At this stage I don't even know what Sigrok is, but I will learn it.

The technical addvices you gave me are great. I am trying make it as noiseless as possible and as affordable as possible at the same time, trying to optimize both is not easy as you know :)
14-bit version is out of question at the moment I am only building the 12-bit because 14-bit is too costly for my price range. I will keep your advises in mind when building the new revision.

Thanks!


 


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