Closing a circuit with the core?

Hello, I am familiar with coding but very new to electronics. I have a device with buttons that activate by closing the circuit, I assume. It look like this on the device: I used a breadboard and was able to trigger the device function just completing the circuit with a simple analog button. I want to trigger the same thing using the particle core. I ran though a couple of the led examples, but they are all generating current is my understanding? Is it possible to just open and close a circuit using the core? Thanks in advance.

@neversummer84, the image you provided looks like a photo-resistor that drops its resistance in the presence of light. Typically, a Core cannot “close” a circuit directly but can drive a transistor or relay to do so. If you can give more details on the “circuit” you are trying to control, we can better guide you. Do you have a schematic?

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It is a thermostat button, so I’m pretty sure not a photo-resistor. A rubber button with a little disk sits on top of that and I assume just closes the circuit. This is what I was doing with the breadboard

@neversummer84, aha! So if you search the forum you’ll find that some members have been able to use a transistor or relay. Those keys use conductive rubber to complete a circuit. You can try using a standard NPN (2N3904) transistor with a 1K ohm resistor between the base and a Core pin to control it. You will need to find the “+” side of the switch to connect to the collector, with the emitter going to the other side. You could also use a FET and this article can give you some guidance.


I was able to create a NPN transistor “switch” with an LED using D0, GRN, and D6 pulsing to the base. I was also able to do the same thing with the thermostat button, using +, -, and a second - to the base. However, if I used +/- from the thermostat and pulsing D6 to the base, nothing happened. Would that be because the core and thermostat are using different voltage? Here is a picture of what I set up that isn’t working when D6 is pulsed. If I move the yellow wire over one to left, then it triggers the thermostat.

You might be able to use an optoisolator. They have an internal LED that controls the conductance of a variable conductor, so you control them by driving the internal LED. The question is whether you can find one with characteristics that match what the thermostat expects from a button press. You also get free air-gapping between the devices, if you care.