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Momentary button behaving as a touch button (unintended). (Video and schematic)
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Topic: Momentary button behaving as a touch button (unintended). (Video and schematic) (Read 1046 times)
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Sysse
Newbie
Posts: 5
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Momentary button behaving as a touch button (unintended). (Video and schematic)
«
on:
April 26, 2018, 04:41:40 pm »
I've been trying to make a toggle switch using transistors. I watched Dave's video (
https://youtu.be/Foc9R0dC2iI
) but I couldn't get it to work, so I tried coming up with my own design, but I ran in to a funny problem. The momentary button doesn't actually have to be pressed (most of the time). It's enough to touch it to turn on the circuit.
This is beyond me and I'm not even sure what to google at this point. I've included a short video (listen for the click of the button) and a beautiful handdrawn schematic.
Any and all idea are welcome!
Schematic:
https://photos.app.goo.gl/phRSDsSl0OWZzvg32
Video:
https://photos.app.goo.gl/ZibzJBReuho79zWD3
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eev_carl
Regular Contributor
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Re: Momentary button behaving as a touch button (unintended). (Video and schematic)
«
Reply #1 on:
April 26, 2018, 05:36:05 pm »
I created a few toggles the other day with a SN74LS74AN D-Type Flip Flop ($0.61 USD from Mouser). You might try to build your own D-Type flip flop from a series of gates like this
https://www.electronics-tutorials.ws/sequential/seq_4.html
And build the gates from transistors like this
https://www.electronics-tutorials.ws/logic/logic_5.html
The IC I used is really simple...a single connection from the switch drives the CLK pin. The output voltage appears on a different pin. PRE + CLR are high. D + ^Q are tied together.
-Carl
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Sysse
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Re: Momentary button behaving as a touch button (unintended). (Video and schematic)
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Reply #2 on:
April 26, 2018, 07:34:27 pm »
Thanks for the tip! For now I'm going to try to figure this out so I don't get sidetracked, but gates with discrete transistors looks fun!
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Jwillis
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Re: Momentary button behaving as a touch button (unintended). (Video and schematic)
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Reply #3 on:
April 27, 2018, 01:54:23 am »
Switch may not be rated for the voltage your putting into it .Probably arcing inside.That would be my guess
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BradC
Super Contributor
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Re: Momentary button behaving as a touch button (unintended). (Video and schematic)
«
Reply #4 on:
April 27, 2018, 04:35:25 am »
You have a very high open impedance on that switch. It is not outside the realm of possibility you are coupling some floating EMI into that switch with your finger. As an experiment, change the 1M to 100K and see if you can still make it happen.
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