Having trouble with flashing outputs on a D flip-flop state machine

Thread Starter


Joined Sep 1, 2015

I am trying to build a state machine using D flip flops. I have attached two leds to the Q1 Q0 outputs and for some reason they are flashing with the clock. I have double checked I have eveything connected to the correct inputs/outputs. Is there a reasob why this may be happening. Could anyone suggest any steps I could take to debug it. I have attached an image of the schematic.

Huge thanks in advance. I am fairly new to electronics - when things do not go to plan I don't really know how to solve/fix.



Joined Feb 26, 2011
Without looking too closely at the functionality of your design, your issue could be floating logic, pull the outputs of the flip flops down to ground using a 10k resistor.


Joined Aug 1, 2013
Your question is missing a lot of information. What is the logic family (CMOS, HCMOS, AC CMOS, ACT CMOS, TTL, ECL, etc.)? What is the system voltage? Where are each end of the LED's connected?

AND - what are the LED's supposed to do? You question implies that they are not supposed to be blinking with each clock cycle, but that leaves a ton of other operational conditions. What does this circuit do? Think about what we might need to know to diagnose your problem, and tell us that.