Delay Hold circuit to turn on mini oscilloscope?

Thread Starter

electronice123

Joined Oct 10, 2008
346
Hi All,

I'm working on circuit which is meant to power several small oscopes and freq gens.
The circuit has one power switch to turn everything on.

The oscopes require the power button to be held for 2 seconds.
The oscope power switches are N.O. and when pushed they pull the +3.3V power to ground.

I have not made the PCB yet, still working on the schematic/breadboard. I have a 4013 on the circuit in which one half of it is not being used.
Initially I thought I could wire up the 4013 to make it a One-shot, then use that to turn on and off a relay with a 2 second RC delay circuit.

My simulation shows the circuit works but the output of the one shot stays on (forgot the 4013 is leading edge triggered) so it would take another leading edge to trigger it to turn off the relay.

What can I do to make this work?
 

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Thread Starter

electronice123

Joined Oct 10, 2008
346
Okay, so I did more work in the simulation and got it to work.

If any of you see a way this might be a problem or it could be made better please let me know.
The 50uF will be replaced with a 500nF to give me a 2 second hold on the switch.
 

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MisterBill2

Joined Jan 23, 2018
19,055
To make the CD4013 reset after some time I have used a circuit called a "Flopshot", which will work with a flipflop that has a HIGH true reset. Use a capacitor from the reset to the V+ common, and a fairly high value resistor from the "Q" output to the reset input. When the FF is triggered the"Q" output goes high and stays high until the capacitor on the reset charges enough so that the FF resets and the "Q" goes low, which discharges the capacitor. Then use the rising edge of the "Qbar" output AND the button input to edge trigger the second FF that controls the power. Then the short press will just trigger the timer and after 2 seconds the next rising edge should trigger it off.
 

Thread Starter

electronice123

Joined Oct 10, 2008
346
To make the CD4013 reset after some time I have used a circuit called a "Flopshot", which will work with a flipflop that has a HIGH true reset. Use a capacitor from the reset to the V+ common, and a fairly high value resistor from the "Q" output to the reset input. When the FF is triggered the"Q" output goes high and stays high until the capacitor on the reset charges enough so that the FF resets and the "Q" goes low, which discharges the capacitor. Then use the rising edge of the "Qbar" output AND the button input to edge trigger the second FF that controls the power. Then the short press will just trigger the timer and after 2 seconds the next rising edge should trigger it off.
I like your idea, but I only have 1 of the FF's on the 4013 available.
 

Thread Starter

electronice123

Joined Oct 10, 2008
346
I figured out another way to do it based on your explanation. Thanks. I was making it more complicated than it needed to be.

To make the CD4013 reset after some time I have used a circuit called a "Flopshot", which will work with a flipflop that has a HIGH true reset. Use a capacitor from the reset to the V+ common, and a fairly high value resistor from the "Q" output to the reset input. When the FF is triggered the"Q" output goes high and stays high until the capacitor on the reset charges enough so that the FF resets and the "Q" goes low, which discharges the capacitor. Then use the rising edge of the "Qbar" output AND the button input to edge trigger the second FF that controls the power. Then the short press will just trigger the timer and after 2 seconds the next rising edge should trigger it off.
 

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