Hi
so I got this project of mine, which I'm working on for quite some time now and making good progress. Most things work quite well and satisfying however one thing kinda destroys my brain on a regular basis.
I get quite inaccurate readings from the ADC and I mostly blame my ground plane design for it as the ground loop for the ADC inputs seems a big large this way.
But how could I improve that?
Here is my project schematics: https://github.com/mamama1/LabPSU_Darlington/blob/master/schematics.pdf
board preview: https://github.com/mamama1/LabPSU_Darlington/blob/master/preview.PNG
Description of the project:
It is (or wants to be) a precision Lab PSU using the Teensy 3.5 as its brain, it's ADC and an external MCP4922 DAC with an external 2.048V reference for both the DAC and the ADC.
The ADC measures this on its channels:
- output voltage right at the darlingtons
- output voltage at an external sense line (only one sense line for now, unfortunately)
- current across an 10mOhm shunt and amplified by a LTC6102
- whether the PSU is in constant current mode or not (basically looking whether there is a certain level of voltage on IC2B's output or not)
I'm always about 1-2% percent off when it comes to voltage or current measurement. Doesn't matter if it is 1V or 10V or 10mA or 3A.
In an earlier release i did use a MCP3204 external SPI ADC which gave me better results (quite bang on, actually), however I wanted to save cost and that ADC was also entirey on the analog part of the ground plane and had it's pins nearer together so I guess the ground loop was reasonably smaller as well.
CC mode works quite well, sub 1% off, so it really seems only the ADC readings are what's not as good as they could be.
Thanks for any advice!
PS: feel free to copy/reuse/fork/follow this repo! Open Source hardware FTW!
so I got this project of mine, which I'm working on for quite some time now and making good progress. Most things work quite well and satisfying however one thing kinda destroys my brain on a regular basis.
I get quite inaccurate readings from the ADC and I mostly blame my ground plane design for it as the ground loop for the ADC inputs seems a big large this way.
But how could I improve that?
Here is my project schematics: https://github.com/mamama1/LabPSU_Darlington/blob/master/schematics.pdf
board preview: https://github.com/mamama1/LabPSU_Darlington/blob/master/preview.PNG
Description of the project:
It is (or wants to be) a precision Lab PSU using the Teensy 3.5 as its brain, it's ADC and an external MCP4922 DAC with an external 2.048V reference for both the DAC and the ADC.
The ADC measures this on its channels:
- output voltage right at the darlingtons
- output voltage at an external sense line (only one sense line for now, unfortunately)
- current across an 10mOhm shunt and amplified by a LTC6102
- whether the PSU is in constant current mode or not (basically looking whether there is a certain level of voltage on IC2B's output or not)
I'm always about 1-2% percent off when it comes to voltage or current measurement. Doesn't matter if it is 1V or 10V or 10mA or 3A.
In an earlier release i did use a MCP3204 external SPI ADC which gave me better results (quite bang on, actually), however I wanted to save cost and that ADC was also entirey on the analog part of the ground plane and had it's pins nearer together so I guess the ground loop was reasonably smaller as well.
CC mode works quite well, sub 1% off, so it really seems only the ADC readings are what's not as good as they could be.
Thanks for any advice!
PS: feel free to copy/reuse/fork/follow this repo! Open Source hardware FTW!
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