Forums » General Electronics Discussion

I am trying to work out how to use a single momentary switch to cycle through 3 LEDs.

For example: LED1: ON LED2: Off LED3: Off

Switch triggered

LED1: Off LED2: ON LED3: Off

Switch triggered

LED1: Off LED2: Off LED3: ON

Return to the start of the cycle

I thought that perhaps JK Flip flops would be the way to do this, but I do not have the experience to work it out. Can anyone provide some insight?

Have a look at:

https://en.wikipedia.org/wiki/Shift_register

I think if you make a 3 bit SIPO, tie the Q output of the 3rd stage back to the D input of the first stage and then preset a single stage to put a 1 into the loop.

Then clock it with the pushbutton. You will need to debounce the switch (search CL for tags on debounce).

Thanks for the input. Does this look correct? (ignoring the values for R)

Connect the LED anodes to 5V, not ground. Or reverse the diode polarities.

Put pulldown resistors from the switches to ground.

Then replace the switches with voltage controlled switches.

Drive them with PWS() sources generating your desired pulse sequence (see: https://www.circuitlab.com/docs/expressions/).

Set up a time domain simulation probing the pulse source voltages and either the flip-flop output voltages or the LED currents.

Set your time steps to no longer than 0.1 times the shortest duration in your pulse sequence (i.e. you clock period).

What does your simulation do?

It may be simpler to start with D-type flip flops and move on to JKs when you've got that to run OK.

Try a CMOS 4017 IC, it has ten outputs but can be configured to use only 3 in a sequence you want, and its all in one IC.