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I'm new to electronics and I've been trying to make a device that reminds my father to charge his scooter when he comes into the garage. Here is the circuit diagram:

Plan for the system

Switch S2 is a footpedal / pressure plate where he will park the scooter. This causes the Buzzer to start making an annoying noise.

Switch S1 is a contact switch attached to the charging port of the scooter. Once the scooter is plugged in, the buzzer will go silent and the LED will light up instead.

I've made a prototype on the breadboard and it works as expected.

Essentially, this is an A.B' logic gate.

The problem that I see here is that, when the scooter is plugged in. I'm basically wasting power by dumping all the current through the transistor to the ground. Is there a way to solve this problem without wasting power? I intend to run this off some solar power and salvaged batteries, so I don't want to be wasting the little charge that I have.

I've tried using the two-way switch, but when both the footpedal is disconnected and the charger isn't plugged in, the buzzer turns on.

Please let me know if there is any clever way around this. Thank you.

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    \$\begingroup\$ Your collector resistor is far too small. Use a larger value resistor to waste less power. Then of course you'll need to amplify the signal to the buzzer with a second transistor. If you're really concerned about power consumption, you should use modern CMOS logic instead of what amounts to RTL that you're using here. \$\endgroup\$
    – Hearth
    Aug 29, 2022 at 15:22
  • \$\begingroup\$ @Hearth I am way too dumb to use CMOS logic, and this is just an enthusiast project. I'm going with the jankiest option available to me, which is in the answer 😁 \$\endgroup\$
    – tsamridh86
    Aug 30, 2022 at 4:08

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Yes, there are ways to make this not waste power (or rather, only waste a tiny amount).

However, why complicate things? Replace S1 with a normally-closed switch (or one half of a double-throw switch) and then you can simply wire both switches in series with the buzzer.

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  • \$\begingroup\$ it's so janky that I love it. Just what I needed to solve this as cheaply as possible \$\endgroup\$
    – tsamridh86
    Aug 30, 2022 at 4:08

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