OSHW USB 4 channel 24bit DAQ with 2 current outputs. ADS122U04 based.

[KZem]

Hello,

I'm new to this forum and for starters I would like to share my latest hobby project.

Its a small, 4 channel 24bit USB DAQ, with additional two current outputs. I have designed it around TI's ASD122U04 ADC, mostly because its one of few adc's that use UART interface (rather that SPI). That tempted me to design a system that would not require a micro-controller (and all the bagage that comes with it), just a simple UART to USB converter.




The main design requirements where the following:
- no uC with dedicated firmware
- 4 single-ended, 2 differential channels or their combinations.
- 2 current outputs
- USB connection and power
- 4 ranges up to 25V, separately set for each channel.
- no dedicated drivers, all software runs in user-space
- small form-factor
- try to use parts easily obtainable


The ADS122U04 has quite a number of features of interest:
- 4 single ended channels, 2 differential.
- 2 Current DAC's (well, not normal dac's, they have just a couple of discrete settings, still better than nothing)
- up to 2kSPS
- 24bit (~20 ENOB)
- fully UART programmable
- has a few GPIO's
- nice SMD package


For the UART to USB bridge i chose Microchip's MCP2200 for a number of reasons:
- has both UART and GPIO (I used those for range selections)
- uses HID interface
- fully specified, inc. register programming
- Python code already published on GitHub

The PCB is 4 layer, made by JLC-PCB

Full hardware design files are published on my GitHub:
https://github.com/Hiperino/DAQ_24bit_Hardware

Those are files for Rev 1.1.0, but the built hardware that I have is 1.0.0, because there where some errors along the way. Still the functionality is the same.

I will publish more details later, along with some measurements and also the Python software.

I'm very eager to hear any comments about this design and hope for a good discussion.

In the future I plan publish more of my current and past projects, as time permits.

Best Regards,
KZem