Electronics notes/General actuator notes, circuit protection

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This is for beginners and very much by a beginner / hobbyist.

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.


Some basics and reference: Volts, amps, energy, power · batteries · resistors · transistors · fuses · diodes · capacitors · inductors and transformers · ground

Slightly less basic: amplifier notes · varistors · changing voltage · baluns · frequency generation · Transmission lines · skin effect


And some more applied stuff:

IO: Input and output pins · wired local IO · wired local-ish IO · ·  Various wireless · 802.11 (WiFi) · cell phone

Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions

Audio notes: See avnotes


Platform specific

Arduino and AVR notes · (Ethernet)
Microcontroller and computer platforms ··· ESP series notes · STM32 series notes


Less sorted: Ground · device voltage and impedance (+ audio-specific) · electricity and humans · power supply considerations · Common terms, useful basics, soldering · landline phones · pulse modulation · signal reflection · Project boxes · resource metering · SDR · PLL · vacuum tubes · Multimeter notes Unsorted stuff

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer ·

See also Category:Electronics.


On driving loads from ICs

This article/section is a stub — probably a pile of half-sorted notes and is probably a first version, is not well-checked, so may have incorrect bits. (Feel free to ignore, or tell me)

Or, 'from control signal to controlling power'


IC IO pins tend to handle 20mA, perhaps 40mA, and sometimes less. This is enough to drive a (resistor-protected) LED or two, but nothing bright, moving, or otherwise interesting.


When you drive something DC that needs more than a dozen mA, the simplest solution is probably to use this pin to control a (BJT/FET) transistor. That is, use it as a switch that takes current directly your power source and through your load.

One small but important detail to that is the current limiting transistor (often on the order of ~1kOhm) between IO pin and the transistor's base/gate. This avoids accidentally drawing part of the current from that IO pin after all, and ensures it pretty much all comes from your real power source.


Regular BJTs tend to be half an amp (maybe two or three in packages like TO220 and others more serious about heat dissipation). You can use a darlington/fetlington arrangement for somewhat higher currents (and higher-gain switching).

Even if you don't need that much power, consider that it's easier to replace a switching transistor than an controlling IC.



When you want to drive AC, you deal with more current, different voltages, a mix of AC and DC. Conceptually, the simplest solution is often to add a relay.


In general, when your load is inductive (relays and solenoids and some other things), you can easily get flyback into your control circuit. You'll want some sort of dissipation or isolation. To protect your IC/transistor from flyback from inductive DC components (e.g. a solenoide), you can use a protection diode.



See also: