Circuit for doing a quick 0 V pulse

[myru28]

I'm building a ring counter and I need to set one of the 7474s I'm using to "1" and the rest to "0" at the very start, so it comes to their set or reset pins a "0" (those pins are active at low level) for the first miliseconds and the rest of the time a "1", so the counter can work properly.

I have already realized that I could use a microcontroller for this but... I find it to be an extreme overkill, I mean, using a microcontroller for executing just 2 instructions (I'm just into building the counter)? Just no... I think there has to be a much more simple circuit that can achieve that but I cannot think of one.

A button isn't also right for this project, the circuit has to be able to initialize on its own when Vcc is connected.

Any idea?

Regards.

 

[BradtheRad]

A capacitor is a simple way to deliver a high or low to a pin on startup.

Then it charges quickly and delivers the opposite state as long as power is applied.

Schematics with scope traces:



The 100k resistor is there to discharge the capacitor when power is disconnected.

 

[IanP]

Look, prices on "small" 8-pin microcontrollers are below $1 (example PICAXE-08 with PICAXE BASIC).
And once programmed they perform much better than circuits build of flip-flops, gates and other discrete components.
These microcontrollers also have internal power-on-reset circuit so they always start from instruction nr.0
I'd use a micro ......
:wink:
IanP