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I'm trying to create a transistor logic OR gate for a key chain, it was supposed to work with two buttons, but just a light touch on the button contacts light up the led brighter than when pressing the buttons, why is that? skin resistance should be larger than pressing the switch enter image description here

enter image description here

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  • \$\begingroup\$ What is the state of the other button at that time? When both transistors are conducting it will light up more brightly that when only one is conducting. \$\endgroup\$
    – Eugene Sh.
    Commented Feb 22, 2021 at 19:05
  • \$\begingroup\$ if i close the contacts with my finger on one button or both, it will light up bright, if i press any button or both it gets dimmer, if i press one button and touch the contacts of the other button it gets dimmer \$\endgroup\$ Commented Feb 22, 2021 at 19:09
  • \$\begingroup\$ Sounds like something is wrong with your circuit. \$\endgroup\$
    – Eugene Sh.
    Commented Feb 22, 2021 at 19:12
  • \$\begingroup\$ Technically your "OR" circuit could just be the two switches, a resistor, and the LED... What is the driving purpose for Q1 and Q2? \$\endgroup\$
    – Ron Beyer
    Commented Feb 22, 2021 at 19:19
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    \$\begingroup\$ I'm wondering if you've really made a capacitive touch switch here. When your finger is near either of the switches it's also near the traces from the switch to the base of the transistor. When connected like this it doesn't take much to trigger the transistors to conduct. If you try pushing the switcher with an insulator like a wooden stick I wonder if the problem will not happen. In that case a pulldown resistor to Vcc from the base of each transistor should resolve it. \$\endgroup\$
    – jwh20
    Commented Feb 22, 2021 at 19:33

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Zooming in your photo, i can see that there is flux on the board. Have you washed your board after soldering? If there is flux left on it, it acts as a conductor (sometimes). It has to be clean. Clean it using isopropanol (if you dnt have isoropanol you can use alcohol but if its not 100% clean alcohol it can corrode your leads)

Other that that, your circuit looks fine, but you may reduce the resistance of your 10k resistors to allow more current through the transistor for your led to switch fully on. Also you can add a pull-down resistor on the gate of your transistor to reduce the capacitive noise created by you, when you get close to your circuit (make sure to use a bigger value resistor for your pull down than your 10k resistors so that more current flows in your transistor rather than ground.

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    \$\begingroup\$ adding 120k pulldown resistors to the input solved the issue \$\endgroup\$ Commented Feb 22, 2021 at 21:12

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