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I've made a capacitive touch/on (currently on bread board) with TTP223 touch IC on active low mode and used 74HC74D as output flip flop. When I use this board near stove and power up the stove spark igniter some times (20% of times) the output of the switch changes.

What is the reason?

  • What should I do to avoid this kind of false operations?

  • Is it possible that the bread board connections or the wires I used act as an antenna and absorb the noise?

This is the schematic I used on flip flop section: enter image description here

Thank you in advance Eric

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2 Answers 2

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CMOS are very sensitive to "external" "pulses".
You should, first, use a decoupling capacitor, nearest possible to Vcc and ground of 74HC74.

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  • \$\begingroup\$ thank you, Antonio for your reply, is a 100nF capacitor enough for the decoupling purpose? \$\endgroup\$ Apr 25, 2022 at 16:55
  • \$\begingroup\$ It is a classical value. Enough for some "spikes". For each IC ... If not, try a higher value as 1uF. A breadboard is not really the best thing near a "spark igniter". \$\endgroup\$
    – Antonio51
    Apr 25, 2022 at 18:37
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What is the reason?

EMI.

What should I do to avoid this kind of false operations?

Proper PCB layout with strong decoupling, possibly with termination resistors on inputs.

Is it possible that the bread board connections or the wires I used act as an antenna and absorb the noise?

Yes.

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  • \$\begingroup\$ thank you so much for your reply \$\endgroup\$ May 11, 2022 at 4:18

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