Pushbutton module #2812 w/NC switch

I have a 2812 and a smaller 2808. I have read all of the forum posts relating to these power switches, and have not seen my question addressed. I am putting my project inside of an old appliance housing. For aesthetics, I want to use the old pushbutton already mounted in the housing. The old button was a “Test” button, that is a normally closed switch, held open when pressed.

With a previous design, I had used a latching relay module that had a normally open pushbutton. The latching relay design was such that the built in switch drove a line low to toggle the relay. With the relay, I was able to add an NPN transistor across the existing relay pushbotton. and keeping the transistor “off” by holding it’s base to ground with the old NC pushbutton. Pressing the button would allow the transistor base to be pulled high, triggering the relay toggle. I can upload a drawing of this if it is unclear.

I have studied the limited schematic of the 2808/2812, but can not tell if this approach would work. I was hoping that there was a way to use the 2808/2812 with a normally closed switch, without the need for the inverting transistor. Is this possible?


There is not a straightforward way to use a normally closed pushbutton with our pushbutton power switches. A transistor inverter can be used with digital logic type inputs, but that is not the type of circuit used to achieve latching on our power switches. You might be able to make a circuit that uses the ON and OFF inputs of the switch (which are digital inputs) along with a transistor inverter.


Okay, thanks Claire. I will experiment around with it a little bit, and see if I can figure it out the same way that I did with the latching relay. If I come up with something simple that works well, I will post it back in this thread for others.

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