Help: Trying to Create Touch Button Circuit

[Zordon]

Im trying to create a touch sensitive button using a 555 chip connected to a 7474 DFlipFlop, Ive connected the penny on both clock and D with no success the LED just either stays on or off and touching the penny has no affect.

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[Nigel Goodwin]

There seems nothing there to make a touch button?, where did you get the circuit from?.

 

[audioguru]

The Old TTL 7474 needs a high amount of input current for a logic low.
If you used a Cmos flip-flop then the mains AC picked up by your finger would clock the flip-flop many times when you touched its clock pin and the results would be random. The Cmos and 555 work fine directly from 9V without a 5V regulator.

I added some contrast to your fuzzy JPG file type sketch. It would be much clearer if you saved it as a clear GIF or PNG file type.

 

[ericgibbs]

hi,
Look here:

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[justDIY]

are you building this circuit to learn from, or for a larger project?

if learning the magic of flip flops and what not, by all means, proceed!

if this is for a larger project, throw out all that old school garbage and go with an integrated solution!

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few notes to heed regarding qprox chips - direct flesh on metal contact is not required nor desired, air gaps are your enemy and plexiglas is your friend.

 

[xxxxxxxxxxxxxx]

Hmmm thats an interesting chip. However, in my opinion, it is cheaper and easier to use the 'old school' chips, as these are not availible where I am and whatnot. By the way, just a few notes on your idea- Should the touchplate not be connected to the 555? I believe this can make a tough switch. Also, I dont feel that the current regualtor you're using is neccessary because CMOS chips run from a wide range of voltaqges, they need not be spot on 5v.

 

[Stellarcore]

I remember playing with something like this a while back, but my method used a 555 timer that was integrated by an op-amp integrator circuit. The touch sensor (also capacitative) was used as part of the feedback loop in the integrator.

After playing around with the frequency/duty cycle of the 555 and adjusting the capacitance of the touch plates (by putting caps in parallel if needed) I could come up with something that "sort of" worked. The only problem was that after you removed your finger from the switch it took too long to recover, but that can probably be fixed by playing with the above parameters.

 

[simrantogether]

very simple concept...

Follow these:

1. if you think the circuit is right then no problem.. use an op-amp 741 or LM 328 for amplifying the electricity coming from your hand .. The op amp is in the multiplier mode at present..

Here's the circuit diagram.. in this attachment you should remove the LM 35 sensor..

2. i hope you know how the touch sensor works... it receives the electricity from our hands.. which is very low... similar to mouse board of laptop... It also receives electricity from your hands...

3. Have you ever tried using laptop mouse board with pen.. it will not work !



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I have more ideas for same project.. if need then i can send you...

Moreover, dont use penny for touch sensor.. because now a days penny's are alloys.. that conduct less..

Use Aluminium foils that are used for packing food...

regards,

simran..