Looking for timer counter ideas

wayneh

Joined Sep 9, 2010
17,496
If I follow you, that circuit will divide by 2 after the high limit. Triggering on every other pulse.
It would divide by much more than that: It would turn any high frequency into 400Hz, since that is the highest frequency that can come out of it.

For sensor frequencies <<400Hz, the timer always resets long before the next sensor pulse arrives, so no problem. For sensor frequencies >> 400Hz, the one-shot gets retriggered almost immediately and the output is at the maximum 400Hz determined by the 555. (The output pulse is a constant interval.)

The timing gets confusing (to me) for sensor frequencies just over 400Hz. The one-shot pulse ends, and then you await a trigger from the sensor. You just missed one and have to wait for for almost one entire cycle for the next sensor pulse. But that's a small impact on the overall pace of the 555, which will be running increasingly closer to its limit.

I suppose this is not a precise approach. 100Hz and 1000Hz would give precise results, but there is a rounded shoulder as the frequency approaches the limiting rate.

It'd be nice to see a simulation.
 

Thread Starter

inwo

Joined Nov 7, 2013
2,419
When I use a 555 in mono mode, it divides by two over the limit.
I'm using a differentiated input.
Don't know how they act when trigger is low past the timing period.
 

Thread Starter

inwo

Joined Nov 7, 2013
2,419
Let me know how to do it, if it works.
That would be super simple. Could even use the boards I have made up.
 

wayneh

Joined Sep 9, 2010
17,496
The trigger needs to be a brief negative pulse (from Vcc down to ground). Perhaps you are having problems with your sensor signal being the opposite, mostly at ground except for a brief positive pulse. You could use the second timer on a 556 to convert the sensor signal into a uniform-length (short), inverted pulse. But maybe just a transistor to invert your sensor signal would do the trick.
 

Thread Starter

inwo

Joined Nov 7, 2013
2,419
Not having trouble at all.
Sensor signal has a pull -up resistor so I can use it to trigger high or low.
Most of my designs use a differentiated input to shorten pulse below T.

If you can think of a way to make a monostable continually output a maximum of 400hz it will simplify my design.

My last diagram seems to work fine. It needs two timers though.
 
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