2
\$\begingroup\$

I have bought an electrical appliance which has buttons sticking out of it. I want to interface with these buttons from a microcontroller, but the buttons are baked on a flex PCB in the underlying circuitry. I can not get to their pins, partly because I'll void warranty, and therefore I decided that a mechanical solution would be best. I would've much preferred an optoisolator wired to the signal lines, but it showed that it can't be done.

I measured the force needed to press the button and calculated that it would be around 4 Newton. (Placed object on scale, zeroed and measured weight while pressing button)

Because the electrical appliance is quite small (approx. 60x60x60mm) and my power supply is limited to 5V 2A I started looking at linear solenoids within this range and found that they are unable to deliver the required force. I then thought of using a stepper motor with gearbox, but this feels a bit overkill.

What are some recommendations to interface with either the physical button or its underlying circuitry, keeping in mind the constraints?

\$\endgroup\$
5
  • \$\begingroup\$ "I can not get to their pins and therefore I decided that a mechanical solution would be best." I question your decision here. It should be possible to interface to the buttons, they might be on a flexible PCB but they also need to interface to something that is (much likely) soldered to a standard PCB. Can you post some pictures of your device? \$\endgroup\$ Commented Sep 4, 2017 at 10:08
  • \$\begingroup\$ I would love to but another reason for not wanting to open it, which I should make more clear in the question, is that I will void warranty \$\endgroup\$
    – Zimano
    Commented Sep 4, 2017 at 10:09
  • \$\begingroup\$ "which I should make more clear in the question" - You can still edit your question and fix that. \$\endgroup\$
    – Dampmaskin
    Commented Sep 4, 2017 at 10:13
  • 1
    \$\begingroup\$ @Dampmaskin I know but I was stuffing a sandwich in my face! Will correct it shortly. \$\endgroup\$
    – Zimano
    Commented Sep 4, 2017 at 10:14
  • \$\begingroup\$ I think that externally (mechanically) interfacing to those buttons will be unreliable as hell. In some cases you'll end up in missed hits, especially on the appliance side. \$\endgroup\$
    – next-hack
    Commented Sep 7, 2017 at 6:47

1 Answer 1

4
\$\begingroup\$

Assuming the button travel is not too much, you should be able to find a hobby servo that can generate that much force at the end of a short arm within your power requirements. This has the added advantage of being very cheap and easy.

https://www.pololu.com/blog/16/electrical-characteristics-of-servos-and-introduction-to-the-servo-control-interface

If a hobby servo will not work for this because of geometry constraints, then a photo of the buttons configuration might get better answers.

\$\endgroup\$
1
  • \$\begingroup\$ Tried it out using one I found at home on a scale and 4N was reached easily. Without any reduction/leverage the circular motion is something to consider in my final design \$\endgroup\$
    – Zimano
    Commented Sep 11, 2017 at 7:18

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.