# Square signal generator - last period problem

Discussion in 'General Electronics Discussion' started by Gr0zn1, Jan 17, 2014.

1. ### Gr0zn1

3
0
Jan 17, 2014
Hello!
I've made square signal device using schmitt trigger. It works on 10Hz, which is a time period of 50 ms. At the output I have a mechanical counter that needs 30ms long pulse to register a count. I get a problem, if I turn off the device when the last period is cut off before 30 ms, so the last signal doesn't get registered.
How could I prolong the last period or make the device turn off only at the leading or trailing edges and not in the middle of a period.

2. ### Harald KappModeratorModerator

9,906
2,098
Nov 17, 2011
Welcom aboard.

First of all, 10Hz = 100ms.
50ms is the on time for a duty cycle of 50%. Is that what you mean?

Second: If you turn power off, any device will turn off, too. To overcome this, you need to supply power even if power is "off". This can be achieved using a soft-off circuit which will take into account the state of the signal generator's output (i.e. turn off only if output is low).

To find a suitable circuit it would be most helpful if you post a schematic diagram of your circuit.

3. ### Gr0zn1

3
0
Jan 17, 2014
Thanks for the wellcome

Yes, you are right...Period is 100ms long, but ON and OFF times are 50ms (duty 50%).

I will use this signal generator for checking optomos relays, if they register all impulses on both sides.

OK I'll explain the whole circuit and post the necesery schematic (some of the parts will be missing).

I will supply my circuit with 9V baterry or external 9V power supply, so first of all I used TLV70436DBVR 3,6V voltage regulator. On the output of the regulator there is a pull-down resistor with a switch closed which makes sure the input of schmitt trigger is driven low and output high before start. Schmitt trigger is equiped with 100k resistor and 1uF capacitor what gives us 1/RC = 10Hz. On the output of the trigger I use a 470ohm resistor and a red diode (2,2V&5mA) connected to 3,6V and 1k resistor that is conected to opto mos relays and on the other side i have a mechanical counter.
So I need good signal generator with controled turn off.

In schematic the codes for schmitt trigger and red diode are wrong (i didn't bother with the specific elements)

I hope I explained it clear enough, because it's a bigger setup with lots of elements, but the biggest problem I get is with not registering the last count because of 30ms limit.

4. ### Harald KappModeratorModerator

9,906
2,098
Nov 17, 2011
Sorry, I cannot access the image on Google drive. All I see is a crossed circle.

One more point: Do you need to turn off the oscillator circuit completely or do you just want to stay it at low level when "off"?