Instructables

Help need Latching Momentary Switch Circuit?

i need to make momentary switch turn on a led and stay on until i hit the switch again. i found a ciruit that i think will work but im having trouble getting it to work
http://www.daycounter.com/Circuits/Latching-Momentary-Switch/Latching-Momentary-Switch.phtml

Patman274 years ago
I am also having the same problem, looking for a latching circuit. I just finished putting together this exact same circuit on a Radioshack learning lab, which has a breadboard with ground and voltage pins. I connected the load to a buzzer, and turned it on. Buzzer stays constant regardless of switch position.
110100101105 years ago
if you still cant make this circiut work there is another option look online for JK flip flop (its a chip with number starting with 40xx or 74xx) connect J and K together to 1 connect the led to Q connect the switch to clk
I'm trying to wire a momentary switch to make it a latch switch also. Would your instructions work for a 7400 dual JK flip flop IC? I'm looking at 7473 and 7476. I'm thinking that if I just use one side of the IC, I can connect the switch to CLK, the led to Q and connect J and K to 1. I'm noticing though that for these two ICs, pin 1 is label CLK. Is this the right pin to connect J and K to for these ICs? I'm looking at diagrams for these two ICs, to make sense of them at this website: http://www.qsl.net/yo5ofh/data_sheets/7450.htm
frollard5 years ago
Thats exactly the latch circuit you want. What behaviour is causing you problems?
blademaster2444 (author)  frollard5 years ago
im not sure whats mess me up but nothing happens when i push the switch. im kind of new to making my own circuits
If you're building it on a breadboard, make sure you have the collector, base, and emitter for your transistors correct. (2 are NPN and 1 is PNP transistor. I didn't check the power transistor's style...didnt look too close) The CBE and EBC on those packages are usually opposite! Make sure you're wired correctly. I find it helps to draw pictures of the actual devices, with correctly labelled pins, then transcribe the circuit to that in different coloured pens. THEN wire the pieces per that new diagram. Pin for pin, and cross off each connection as you make it. Check it twice, then thrice, and plug it in, see what happens. If you are in a non-static-safe environment your transistors may no longer be transistors, and are now modern electric-discharge-destroyed art :D