Repeating circuit: 1, 2, 3, 1, 2, 3...

[Don Gilmore]

Guys:

I'm an ME working on a small project where I'd like to do something ridiculously simple, yet I keep coming up with complex solutions. There is probably a simple way to do this that I am missing.

What I'd like to do is cycle between three outputs--let's say three discrete LED's--in a continuous circle using a square wave clock input. If the LED's are numbered 1, 2 and 3, I want them to cycle 123123123123... The inputwould be the square wave from a function generator and I'd like to controlthe speed of the LED's by the frequency.

I keep coming up with complicated ideas like using a counter that outputs to a decoder. Surely there is an easier way?

Don
Kansas City

 

[Don Gilmore]

A 4017 decoded decade counter, connected to reset at three. If the

current is low enough, the LEDs can be driven directly.
http://www.datasheetcatalog.org/datasheet/philips/74HC4017.pdf

I thought about a 4017, but didn't know that I could reset it at three. How is this done? Would I connect output 3 to the reset line? It is important that each output gets equal time...no pauses or skipped pulses.

Don

 

[petrus bitbyter]

I thought about a 4017, but didn't know that I could reset it at three.
How is this done? Would I connect output 3 to the reset line? It is
important that each output gets equal time...no pauses or skipped pulses.

Don

Connect Q4 to MR and the counter resets immediately after the 3rd pulse. So
you will have a short pause in the ns area between pulse 3 and puls 1. You
may need to lengthen it somewhat if the Q4 does not fully reset the counter.
A diode and an RC will do that trick.

An alternative is a synchronous serial in parallel out shift register. "NOR"
the first and the second output and feed back to the serial input.

petrus bitbyter

 

[whit3rd]

I'm an ME working on a small project where I'd like to do something ridiculously simple...
What I'd like to do is cycle between three outputs--let's say three discrete LED's--in a continuous circle using a square wave clock input. If the LED's are numbered 1, 2 and 3, I want them to cycle 123123123123... The input would be the square wave from a function generator...

I'm not sure why a function generator is useful, but if you have one,
set it to a ramp waveform (sawtooth) and use a bargraph display
chip (LM3914 or somesuch). One chip and the LEDs, and you're done.

Decoded counters (CD4017 in CMOS, SN74142 in TTL) are also available in a single
chip, you just need to worry about reset setup and hold times when you truncate
their sequence.

 

[ehsjr]

You're over thinking this a bit

And it appears you're under thinking it. The op wants to control
the leds with an external generator:
"The input would be the square wave from a function generator and
I'd like to control the speed of the LED's by the frequency."

I don't see where you or David has addressed that with the picaxe
idea in any of the posts in this thread.

Ed