Asynchronous pulse generator

[Eudoxus]

So I've been out of the electronics game for a while, and I wanted to run this circuit past you guys to make sure I'm not doing anything dumb...

A project I'm working on needs a pair of matched 5V square waves, 5-10kHz, 180 degrees out of phase. It's a quick-and-dirty, jellybean and veroboard type of gig, so nothing too fancy. I decided to use a 555 and LM393. I thought about using a CD4096, level-shifting the 555's output down, but the comparator method seemed more fun.



Sorry the schematic's slightly messy. Please tell me if I'm making any rookie mistakes. Like I said, it's been a while...

[T3sl4co1l]

Not sure why the thresholds... they aren't quite right.

The outputs need pull-ups, because the comparators are open collector type.

The bottom 393 has negative feedback.  It may oscillate on the switching edge.  LM393 is a little bit faster than the 555, so it may be fine anyway (certainly without the feedback resistors), or it may make one or two extra pulses during the edge.

If the frequency is quite low, simply using a logic inverter will do.  74HC04 is fine at 5V.  Use a CMOS 555 and you can run the whole thing from +5V without worrying about dividers between stages.

If you don't mind discrete solutions, this is accurate within 20ns or so between rising and falling edges:



A couple values would have to be changed to run from a 555 and at 5V.

If you don't mind buying ICs, a CD4047 will work on 5 or 9V, and does precisely what you want, out of the box.

Tim