I have an analogue sensor with a signal of 0-12v, I'm then using a voltage divider with R1 100k and R2 33k.
I can read this using an MCP3008 connected to a raspberry pi 3 then multiply the 10bit value by 12_and_a_bit, all good.
The analogue signal has it's own display, when not connected to the pi/MCP3008 this reads a noise of <0.1% of the signal. When I connect the internal display of the probe shows the noise goes up to ~5% of the signal value, this noisy output is also read by the pi.
- The analogue signal ground is tied to the raspberry pi/MCP3008 ground rail.
- I don't think I have especially long wires, 200mm is the longest.
- I tied all the other MCP3008 channels to ground (and they read 0), nothing should be floating anywhere.
- If I plot readings the 'noise' is loosely oscillating about 3-4 seconds.
Has anyone any experience of this? Is there a way to reduce or eliminate it? Can I just add diodes to the signal and ground between the sensor and MCP3008 or is it due to reading the signal?
Thanks for reading this :)