I'm making a little flashlight that'll turn on and off with a push button, but the problem is that my push button changes 3.2 V into 2.8 V.

I don't know if it's a normal issue or how to fix it. Any help would be appreciated.

  • \$\begingroup\$ What's the button's datasheet? What's the current? What do you mean "changes form 3.2 to 2.8". Votlage doesn't exist in isolation, it must be referenced to something. What is the votlage across the switch? \$\endgroup\$
    – Puffafish
    Sep 22, 2022 at 10:18
  • \$\begingroup\$ What I mean by changes from 3.2 to 2.8 is that the battery output 3.2V and but at the exit of the button it's only 2.8, mabe it's due to the led that is after ? I don't have any datasheet but I've tried with a simple slide switch and it does the same. \$\endgroup\$
    – Eli-ott
    Sep 22, 2022 at 10:39
  • 1
    \$\begingroup\$ "mabe it's due to the led that is after" DingDingDingDing! Yes it is. I suggest taking a look at learn.adafruit.com/lets-put-leds-in-things/from-scratch \$\endgroup\$
    – MrGerber
    Sep 22, 2022 at 10:48
  • \$\begingroup\$ Thanks a lot I'll take a look at it ! \$\endgroup\$
    – Eli-ott
    Sep 22, 2022 at 10:52

1 Answer 1


Likely it has nothing to do with the switch. If you have a button cell battery and connect a LED directly, without any current limiting resistor, the battery output voltage will drop to the level of LED forward voltage, current being limited only by the internal resistance of the battery, LED, and wires. Which means the current can be too large for the battery or the LED.

  • \$\begingroup\$ Thanks for the anser, people told me to use a current-limiting resistor, but I don't really know how to use it properly. Also my led is rated at 3.1V and the batteries output 3.2V so a 100 ohm resistor would be a little too much I think. \$\endgroup\$
    – Eli-ott
    Sep 22, 2022 at 10:51
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    \$\begingroup\$ It depends what is useful. LEDs are like bikes or cars, it usually makes no sense to drive them constantly at maximum they are capable of. \$\endgroup\$
    – Justme
    Sep 22, 2022 at 11:00
  • \$\begingroup\$ That's a fair point. So aiming for like 2.9V would be good I think. \$\endgroup\$
    – Eli-ott
    Sep 22, 2022 at 11:04
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    \$\begingroup\$ @Eli-ott, Re, "aiming for...2.9V." Your aim with LEDs should always be to control the current, not the voltage. An LED has very low impedance near its normal operating point. That is to say: A tiny change in voltage can cause a huge change in current. The page to which MrGerber referred you does a bang-up job of explaining why a battery-powered LED should have a ballast resistor to control the current, and it explains how to calculate the resistor value. You promised to read it. You really should do that now. \$\endgroup\$ Sep 22, 2022 at 12:57

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