555 / 74LS107 Problems

Thread Starter


Joined Oct 4, 2013
Hi everyone,

I am trying to use a 555 to drive a 74LS107 JK flip flop.

I am using a 36k and 18k resistor, and a .1uf capicator. The 555 is producing the expected clock at a 75% duty cycle.

However, the Q output of the 74LS107 is following the output of the clock, instead of only flipping on the negative edge. I have the J, K, and CLR lines all tied to positive.

Pictures of the project and the scope are attached.

I am a newbie at this, just trying out some projects for personal enjoyment, so I suspect I've done something dumb. But I have tried replacing chips, looking for wiring faults, and am now out of ideas.

Thanks for any help!



Joined Oct 2, 2009
Glad we can help.
Next time get help fast from AAC.

100μF across the supply might do the trick, but do put a 0.1μF capacitor across pins 1 and 8 of the 555 circuit!