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I am trying to reduce noise on an analogue sensor. I have scanned many forums for answers and spent multiple hours / days on finding the optimum solution. I am using ACS712-based sensors and the need is for accurate readings in milliVolt. This is my first project, so please excuse my ignorance.

I submit my solution for comment.

Diagram

I am unsure of the wiring of the TL431. TL431 is to provide stable power supply to MCP3008. Sensor input contains a capacitor from sensor to ground. Unused pins on MCP3008 are grounded. Shielded cable is used from RPI to sensor.

I am using the following sensor:

30A Current Sensor Modulehttps://www.jaycar.co.nz/arduino-compatible-30a-current-sensor-module/p/XC4610

Please provide any other suggestions to improve the noise reduction.

Thanks Herman

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  • Appendix H, I of my answer below show how to use TL431 and another external voltage reference. stackoverflow.com/questions/71949863/…
    – tlfong01
    May 3, 2022 at 7:30
  • There are a couple of ways to reduce noise, including: (1) use differential input, (2) use 16 bit or 24 bit resolution and ignore the lowest bits.
    – tlfong01
    May 3, 2022 at 9:04

2 Answers 2

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You have specified insufficient information e.g. sensor specifications, distance (or evidence of a problem) for any meaningful answer. This is NOT a Pi specific question as the solution would be the same for ANY processor).

Wiring low voltage analog sensors is an art (maybe a black art) - some general pointers.

  1. Use twisted pair (shielded if necessary).
  2. Wire the ground of each sensor individually and have a single connection (no loops or common wiring) to an analog ground.
  3. Keep analog & digital grounds and wiring separate.

You do not seem to understand the operation of a shunt regulator - it needs an external resistor.

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    Milliways: Thanks for your improvement suggestions. Regarding your comment "You do not seem to understand the operation of a shunt regulator - it needs an external resistor.". Would you be able to suggest a resistor circuit? I am using the following sensor. jaycar.co.nz/arduino-compatible-30a-current-sensor-module/p/… May 3, 2022 at 0:19
  • Milliways: Your comment "Keep analog & digital grounds and wiring separate.". Would it be advisable to separate the RPI power supply and the analogue power supply totally apart? How does the sensor then interact with the RPI without a common ground? May 3, 2022 at 0:27
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    Milliways: "Use twisted pair (shielded if necessary)." What do you twist? Signal-out and ground? May 3, 2022 at 1:30
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Don't try to get to the perfect solution in one step. Instead, build a simple prototype that works and check how good your measurements are. There's a chance you don't need a separate voltage regulator or any other advanced noise reduction measures.

Your immediate problem right now is that you power your ADC with 5V, which makes is unsafe to connect it to the Pi which uses 3.3V.

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