I would like to ask a question regarding the current prototype I am designing for a monitoring system using Raspberry Pi, an ADS1115 ADC and analog/digital sensors. Below is the schematic of my current prototype

enter image description here

I am powering two analog sensors (PH-4502C, TDS Meter Gravity) at +5V, a DS18B20 digital temp sensor at +3.3v, and float switch sensors at +3.3v as well using a MB102 power supply. I chose this since I'd rather have external power for powering this prototype to reduce sourcing too much power from my RPI for this node as I consider integrating it with other circuitry to build larger systems in the future. The MB102 is also powered using a 12v 1A adapter.

My question lies with the ADS1115 ADC. I am considering in powering it also from the +3.3v off the external supply, however, I am not sure if what other considerations should I look into aside from the VDD I am supplying to ensure accurate readings are being made.

With that, my questions are as follows:

1.) Is the direct +3.3v supply to the ADC appropriate? Would I be better off on using the RPI +3.3v pin instead?

2.) In context with 1, do I provide common ground with the RPI using the MB102 ground? or with the +12v ground? What would be the difference in this case?

3.) Would I need extra components for somehow creating a more stable and safe circuit for my sensors, ADC, and the RPI?

4.) I am also looking into using a CAT5E cable for extending the wiring off the RPI to the prototype with maximum length of 1 meter. How would this affect the quality of data transmission from ADC to the controller? Would direct connection still be okay as it is?

Datasheets for reference:


MB102 Breadboard Power Supply



PH4502C pH meter Sorry but I couldn't find a proper datasheet for this so here is another reference link instead


1 Answer 1

  1. Think what happens if you power up one board before the other - If you don't have answer to that, maybe use one 3.3V supply for everything.

  2. All grounds of all devices must be connected together, just like MB102 grounds are already. If you don't provide a good ground connection between devices, current return paths may go via IC data pins, which can damage devices.

  3. If it works, no. Do note that the ADC address pin is floating and it won't reliably have an I2C address.

  4. If properly designed, such as proper bypassing of supplies and choosing the wiring in a suitable way, it should work, but just randomly wiring it without thought will lead to problems.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.