MicroPython Forum (Archive)

In the original schematics IN+ is shifted to 2.5 V i.e. should output about 32767, as you observed.
The wiring of the input divider resistors is so, that the voltage at Vin is multiplied by a ratio of 38.1k/2038.1k i.e. it is reduced to about 1.8% of the original value. So if your input voltage varies by about +/-4V it would yield 75 mV variation at IN+ resulting in +/-980 measurement value.
This fits nicely to what you abserved.
So the voltage divider resistors seem to be the problem.

I agree with Robert to remove R5 + R6. They could possibly be replaced by other limiting diodes of the TVS type which clamp the input to about 2.5 Volts. R3+R4 are still much to high. In the datasheet an input leakage current of 1 uA is mentioned and an OPA for bringing the input source impedance to below 200 Ohms recommendend. Perhaps a R3+R4 value of 100-330 Ohm is a good match.

I'm working with gained photodiode that outputs 0-5V, so clamping to 2.5V will be a problem for me.
Is this something achievable using the current ADC11 Click schematic? or should i look for another LTC1864 module?

Thank you for the support,

You could remove R7 and C3 and make the connection between IN- and GND of the module. Then you have the full 0-5 V range. If you do not need fast sampling, you can keep C3.

You get similar results by:
- removing R7 and R6,
- replace R3 and R4 by a wire or resistors with a smaller value, like R6 and R5.
- Connect IN- with the board GND.
Then you still have IN- and IN+ for connection, and a range of 0-5V.
In any case you have to run a calibration to match the values you read with the real voltage and eventually the light intensity.

Hi,
After reworking the PCB as you suggested its works like a charm, both code provided and 0-5V range.

Thank you!