Ugly Clock?

Speaker

External difficulties.
I am trying to run a NTE3101 optocoupler into a NTE4029 counter.· I want to monitor rpm.· Using a debounced switch, the counter works great.· Using the 3101, strange things happen.· Do I need to condition the output of the 3101 so that it looks more like a clock pulse.· I don't have a scope so I am just assuming that the problem is a waveform issue.· Voltage out is over 8 on a 9V supply.· The debounce switch is putting out less than that, so I don't think voltage level is a problem.· Rise time fall time?· The 3101 is a darlington pair in the detector.· I would think that rise and fall would be very abrupt.· Suggestions?

PJAllen

You should include a schematic of your circuit (it's easy enough to do with Paint -- just fake it till you make it) so that we can dispense with assumptions.

You have the optocoupler output (collector) "tied HI" with a 4K7 resistor, the emitter at Ground, and the junction of the output and the resistor going to the counter input?

Chris Savage

Hello,
·
·· Typically a Schmitt Trigger is used to clean up pulses from an Opto-coupler.· This has the effect of providing a dead band where no transitions occur.· Basically it prevents oscillation from noise around the normal switching threshold for the logic.· Take care.

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Chris Savage
Parallax Tech Support

Speaker

Thanks for responding.· I have tried several times (w no luck) to upload a .bmp file.· I am using dialup on a sprint card on my laptop while driving so am tolerant of errors.· No, I wired it up w 1k resistors on the negative sides of the emitter and the detector.· Couldn't find a schematic, so I guessed.· Took my output from between· the detector and its resistor.· When coupled, output would be high.· Looking at max I values on datasheet, I thought that perhaps 1k was too much.· If 4.7k is the standard, I will use that.· I will also add a schmidt trigger.· Thanks again.