I have a circuit board with a button in it (the clear white button pictured below is the one I'm targeting). I need to somehow remove the button from the circuit and put a relay in it's place. I'm assuming that the easiest way to do so would be to simply connect the ends of the relay to the correct leads of the button, and if I'm not mistaken, the button would simply be shorted out.

Could someone help me in choosing which leads on the relay should be connected to which leads on the button?

Here are the pictures: button 1 button 2

If you need any more pictures or info, let me know

edit: I don't have a schematic but here's the bottom of the board with the 4 leads of the button circled: bottom

  • 1
    \$\begingroup\$ Do you have a schematic for the circuit board or the relay. If not for the board, could you take a picture of the back showing the traces? \$\endgroup\$ – Justin Trzeciak Mar 8 '14 at 22:44
  • \$\begingroup\$ @jrtzeciak I've added the back of the board. \$\endgroup\$ – Sam D20 Mar 8 '14 at 22:49
  • 1
    \$\begingroup\$ Typically tactile buttons like that are a SPST switch (en.wikipedia.org/wiki/Switch#Contact_terminology). When it is pressed down, two of the pins are connected to the other two pins. Since it looks like the two pins on the right are in the same copper region, they are probably common to one another. As are the two on the left. You can verify this with a multimeter. When the button is pressed, all 4 pins should be connected. Otherwise, the two on the right will be connected, and the two on the left will be connected, but not all 4. Can you verify this? \$\endgroup\$ – Justin Trzeciak Mar 8 '14 at 23:03
  • \$\begingroup\$ I'm at a hackathon right now and looking for a multimeter as we speak. Will report back on that. Thank you for the help. On a side note, if I read correctly, you're saying that the two leads on the left are in the same copper region. But the bottom left lead seems to be isolated from everything else. Is this pin useless and should I ignore it? From what I'm seeing, I think my best bet is to connect the relay to the top left and top right pins. What do you think? \$\endgroup\$ – Sam D20 Mar 8 '14 at 23:29
  • 2
    \$\begingroup\$ The two on the left are probably electrically connected within the switch. The bottom left pad is probably there to make it easier to solder. It doesn't look like the board has proper pads. Top left and top right sound good. Just make sure you connect the switch of the relay and not the coil (not sure what your experience is...). \$\endgroup\$ – Justin Trzeciak Mar 8 '14 at 23:50

The button which you have is related to a fairly common family of buttons called B3F. A button like that would usually be Single Pole Single Throw (SPST) Normally Open (NO), as @jrtrzeciak had mentioned above.

enter image description here

It's good that the PCB, which you're dealing with is single-layer. That makes it easy to trace the signals.

I think, the button is connected like this:

enter image description here

Furthermore, if the button is indeed NO, you don't need to remove the button. You can connect the reeds of the relay in parallel with the button. You'll just have 2 switches (relay and button) in parallel.

  • 1
    \$\begingroup\$ B3F is just Omron's series number. Generically, they're called "6mm x 6mm tact(ile) switches" and there are many, many manufacturers, and various options as the actuation force and actuator height. \$\endgroup\$ – Spehro Pefhany Mar 9 '14 at 0:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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