Push Button to Drive Power to Servo

Question

I am currently doing a project for a class which uses a few other components such as an LCD, a servo, and such. I want to use a button which acts as a circuit breaker on the Vin of the servo in which the servo will only be powered when the switch is pressed. I wanted to implement something like this because I wanted to minimize the power consumption and also acts as a mechanical counter-measure in case the servo keeps on spinning in unwanted situations, such as having the servo entangled by hair or something like that.

I know that I can just connect the button to the I/O pins but I wanted to rely on a hardware solution for power minimization and safety reason.

The servo draws 170mA when idle and can draw a maximum of 1.2A, but I believe it will only draw about 500-600mA with the intended load. It can run between 4.8-6V.

So my question is, would my circuit configuration work for my application? Would it be safe? Do I need any other additional components? Thanks for anyone that can help!

Answer 1

There is a chance that this arrangement could damage the servo and possibly the Arduino. The problem is that, depending on the internals of the servo, it could try and draw power for the servo through the data pin when the button is not pressed. This would both over-stress the internals of the servo and the internals of the Arduino's GPIO pin.

What you could do to mitigate that is to connect the servo's switched power to another GPIO pin of the Arduino, which is set as INPUT. That will then tell the Arduino when the button is pressed and when it's not pressed. Then you use that information to attach and detach the servo in your code so it is only being actively driven when the button is pressed.

Answer 2

Yes, that should be safe, as long as the button can conduct the needed current. That depends on the type of button. You can simply test this. If the button get's hot, it is too small for this.

If it should happen, that the button cannot conduct the needed current, you have 2 ways to go:

1. Just use a bigger button. You can buy buttons, that are meant for mains supply, which will be able to conduct way enough. Every button, that you buy (at least at electronics shops, maybe not on aliexpress or ebay), should have some kind of data sheet, which states the absolute maximums for the electrical characteristics. A maximum current can be found there.
2. You can use a MOSFET (that is capable of providing the needed current) and control it with your button. That would be the way to go, if you really need or want to use this specific button.