Hi to everyone, components I use: Arduino MEGA, NPN BC548 (hFE=222), R1=15K, ublox GPS receiver (max 50mA @3v3) my configuration Arduino 3v3 pin connected to ublox (+) pin ublox (-) connected to BC548 collector pin BC548 emitter pin connected to Arduino GND R1 connects Arduino's D9 with BC548 …

Unstable NPN switch circuitry

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