[SOLVED] Sensor output high for >30secs, but I need a short pulse

[Captain_Mainwaring]

Hi all,



I have a design that I need help and advice with. I have a sensor that is triggered when a physical action happens (a bit like a jack in the box) and the output remains high until it is reset by replacing the moving part back into its "loaded" position. However, I would like to use circuitry to get a short pulse (maybe ~50ms or so) when the rising edge of the sensor is detected.



What sort of circuit would do for this?



Thanks,



George

 

[kripacharya]

any edge triggered mono-shot circuit will do the job. Depending on your sensor output, you might want to precede that with a schmitt trigger gate.

50mS is a longish period - what is this to be used for ?

 

[crutschow]

555 timers are commonly used as a one-shot (monostable multivibrator) but for your requirement of a positive edge-triggered circuit with a long duration trigger, the CD4047 would give a simpler circuit (just one external R and C required).

If the trigger pulse has a ratty edge then you may need a Schmitt trigger such as a CD4106 to clean up the signal. You can experimentally determine the need for that by first trying the one-shot without it.

 

[BradtheRad]

A 555 IC is easy to use...

Although if you wish to experiment with simple transistor circuits, this illustrates how a positive input can produce a positive pulse for 50 mSec.

The snapshot shows an overall timeframe under 1 sec.

After the incoming signal is removed, the capacitor discharges through the 1M resistor. In a few seconds it resets and is ready for the next use.

 

[Captain_Mainwaring]

Thanks guys for all the input, some really good ideas and advice here!!!

To kripacharya, I just need a pulse that is long enough to be picked up as an input by an Arduino digital input pin. I thought 30-50ms would be a nice long pulse to ensure the Arduino got it!

Cheers,

George