Measure 12 VDC motor safely with an IC and a voltage divider

Question

I have a project with 16 DC linear actuators. They are all 12 V and use up to 5 A when in collision with each other or when they just reach their course limit (either up or down), and just about 1 to 2 A in normal operation.

I initially wanted to use a Hall current sensors like the ACS712 for each motor to detect when they are in collision (or reached their linear limit) and turn them OFF very fast with some IC like an Arduino, but that easily becomes very expensive so I am opting for a Smshunt configuration with a 1 or 0.1 Ω resistor and a voltage divider in between and using Ohm's law to compute the load on the motors to kind of "detect collision".

My problem is with the voltage divider (that should be connected to an Arduino), and the inductive spikes or whatever comes back from the motors that will damage the IC.

I use an H-bridge configuration with relays and a protection diode between motor terminals, but am I still unsure if the noise coming from the voltage divider that measures the voltage drop between the shunt resistor (that's connected to the motor) is safe to connect to my Arduino.

If not, how can I isolate it or protect it? Is there a way to make optocouplers relay voltage information to the IC in an isolated way? Is there a safe and cheap alternative way to solve this problem?

Answer 1

I am assuming they are all on the same power supply. One possibility is to measure the current of all of them and with a bit of processor logic you can detect the change in current when a collision happens as you know what it should be under normal conditions.

You can use a resistor between the sensor such as a shunt and the A/D to protect from spikes. The values etc depend on the A/D chosen as there are many different input protection schemes. You can also place diodes after the resistor to clamp the transient signal to the VCC or Ground. Placing a small cap between ground and the A/D side of the resistor will help clean up the signal.

If you select shunt resistors to measure current place them in the ground side in front of the H-Bridge then you do not have to hassle with offsets and isolation.