Momentary to Latching Switch Conversion With This Simple Circuit

by BenBuildsDIY

13K3711

Intro: Momentary to Latching Switch Conversion With This Simple Circuit

Have you ever wondered if you could use a wee little momentary tact switch to turn large high voltage high current things on and off? Wonder no more!! Use this instructable and the circuit schematic to build yourself a latching circuit!

STEP 1: Watch the Video


First things first, watch the video and see how I built the circuit. The video is all encompassing, but further on in this instructable you will find some more detailed instructions and some tutorial videos.

STEP 2: Gather Supplies

For this circuit you will need:

1 N-Channel FET

1 PNP Transistor

1 330nF Electrolytic Capacitor

1 Silicon Diode

3 10k Resistors

1 100k Resistor

1 1M Resistor

1 Push Switch

STEP 3: Learn to Breadboard (optional)


If you don't know how to use a breadboard, watch this video tutorial.

STEP 4: Prototype the Circuit on the Breadboard and Test

Start by using the schematic above to prototype the circuit on a breadboard and test it. If it doesn't work, check your connections!

STEP 5: Transfer the Circuit to Perfboard

Once you have built and tested the circuit on a breadboard, proceed to transfer the circuit to a perfboard. Perfboards are basically a bunch of holes with circular copper pads on each hole. Transfer the circuit, following your breadboard and the schematic. Don't forget to solder everything up!

STEP 6: Done!

Congratulations, you're done! You can use this new circuit in conjunction with a relay to control high voltage high current loads using a very small switch! Each time you push the switch, the circuit changes state. Push once to turn everything on and hold it there and again to turn it all off.

Please, if you liked my YouTube video, feel free to subscribe! http://goo.gl/WFgbYb

10 Comments

byronjeffrey 5 years ago

Also, can you use any N-channel mosfet for this? Is it possible to use an NPN transistor instead?

byronjeffrey 5 years ago

Hello, what kind of relay are you using in this circuit? Would this latching switch alternate between two lights? Thanks!

Tiggelen 6 years ago

Hi, on what voltage does this circuit operate?

UtkarshVerma 7 years ago

Please suggest a cheap MOSFET for this circuit

MirandaD7 7 years ago

Hi Ben, I may be wrong or asking a dumb question where does the silicon diode go? Is there any way you could email me on dylan4494@hotmail.com and give me a hand. I need to replace the push switch in this circuit with another relay which will be triggered with a wireless remote. Bit of a long story but I just can't seem to get the circuit working. Can you send me more photos of the circuit built? Even just some close ups of the circuit on a bread board.

BenBuildsDIY 7 years ago

Hi there!

No question is dumb! The silicon diode goes right across the output of the circuit (the part that goes to the relay coil.) It goes in so that it is not forward biased. As in cathode of diode to negative of output. If you are really in doubt, you can just omit it. It is good practice to add it in, but I would say 90% of FETs can handle the small reverse polarity current pulse that the collapsing magnetic field in the relay coil makes. Good luck, and thanks for watching/reading!

BeachsideHank 8 years ago

This is a very handy circuit to use with a hacked cheapo wireless doorbell, simply use the receiver's output to trigger the latching circuit, now you've got a true on/off wireless remote and who can't use one or more of those?

Nice work Ben, keep 'em coming.

BenBuildsDIY 8 years ago

Thanks Hank, I'll have to check that out!