Arduino - Raspberry Pi Pico - Raspberry Pi  universal sensors/modules

Hi Gary,

In theory, all 3.3V logic level sensors should work with Arduino and RPI products, since the Arduino can detect the 3.3V level from the sensor output as a logic level high. All logic-level controlled 3.3V actuators can be driven by both Arduino and RPI products too, provided you use a resistor, or ideally a voltage divider, which is ultra low-cost and small, since it's just two resistors. If you're seeing 3.6V logic levels, a single resistor should be fine in series with the line, it may not need a voltage divider, i.e. you can current-limit to prevent damage. With slow sensors, a single 10k resistor may be fine, otherwise consider (say) 1k. For hobby-grade projects, I think this is not an unreasonable balance between cost, effort and risk.

All 3.3V logic level I2C devices can be connected to Arduino and RPI too, since the I2C resistors can be connected to 3.3V if they are not already connected there (disable any pull-up to 5V in software if the Arduino does that).

For UART devices, again the 3.3V devices will be compatible with Arduino and RPI, provided that if the transmit direction from Arduino to the device is connected then a voltage divider is needed. This only leaves SPI as the difficulty, for which level converters would most likely be needed, if you were using the Arduino Uno - but in many cases the SPI devices are more complex and may need the performance of an RPI product rather than Arduino anyway.

In summary, it's definitely better to standardize on 3.3V logic in my opinion, unless you really can't find a suitable 3.3V level sensor at a reasonable price, in which case you have no choice but to do level conversion in some way for signals coming into the RPI products. Also, there are many development boards other than Uno, and they almost all use 3.3V logic levels, e.g. many of the other Arduino boards.

Another point is that although Arduino Uno will work with 3.3V logic level inputs without level conversion, the 3.3V microcontrollers won't work with all devices that accept 5V logic levels, without level conversion. So it's yet another reason to prefer 3.3V logic level devices.

Series resistors may work, but the builder really doesnt have real control of signal's input voltage unless they have a true knowledge of the controller's DI input impedance. Voltage dividers with 2 resistors isnt going to kill my pocketbook, and I can set them pretty reliably.

A better solution is a sensor that can accept 3-5V input, and ~3V output that I'm sure wont drive above a controllers (or accessory) 3.3V power supply. 

Another example is the HC-SR04 ultrasonic ping module that operates at 5V, now there is a newer version HC-SR04P with input voltage range of 3V-5V.

The discussion I'm trying to stimulate are what other sensors besides a SR602 and SR04P have newer modules with 3v to xx input and 3V discrete output.

Good Question. I'm not sure if a list of 3v3 modules exists, it would be nice if one existed. I did a quick search and noticed this PIR sensor which I have never tried before which claims to operate on 3.3V :

https://www.universal-solder.ca/product/pir-mini-motion-detector-sensor-12mm-diameter-am312-chip/  (Available from other resellers I'm sure)

Based on this PIR sensor: http://www.image.micros.com.pl/_dane_techniczne_auto/cz%20am312.pdf

ROFL - working on a RPi project.....using 3.3v to fire a MOSFET,  tried several different mosfets types, all the gates spec'd 2-4v , 2-5 v, 3-5 v to fire fully, 3.3v wasnt turning any of the mosfets fully on, to a 12v 250mA load.  The bipolar transistors in my inventory all were 200mA or less.

Used a 3 to 5 v level shifter to fire that mosfet from gpio, a real rube goldberg. I was determined not to use a relay :-)