What electronic component can interrupt a powered circuit?

Question

I have an IoT project in which I want to leverage existing bicycle LED lights, which have their own battery power. So, rather than using the current from the microprocessor to power the lights, I just need a way to wire my logic board to the bike light and control the on/off of the light.

I don't have an electronics background, so this might be a very elementary question. Is there an inexpensive electronics component that I can somehow wire or solder onto the bike light that can be controlled by another low-voltage circuit?

The ideal component would be able to switch rapidly on and off, preferably without sound / mechanical parts. I'm envisioning wanting to strobe the lights quite rapidly, again, controlled by the logic board.

If there are more than one kind of component, which might be the best for a small, DIY wearables project? IE: low-cost, easy to hook up, easy to source.

Answer 1

Relay:

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Advantages: simple, very well isolated, very little loss of power in load

Disadvantages: relatively slow (perhaps 10s of Hz), needs a fair amount of control current (typically more than logic circuits can supply)

Transistor (BJT shown):

^{simulate this circuit}

Advantages: fast (easily up to Mhz), very small control current (typically < 1/50th of load current) required.

Disadvantages: No isolation, voltage loss across transistor switch, may be harder to wire up. Can't control AC circuits. Relatively low controlled output voltage - depends on transistor, can get >100, but typically less than 30V

Answer 2

Relay: easy to operate and understand, robust, commonly used in cars, available in a range of sizes of which the smallest is "reed relay" (~1cm). Has a rated maximum number of on/off cycles. Not "polarised", so you don't need to care about circuit polarity. Good for large currents and voltages, and AC. Not so cheap.

Transistor (bipolar): somewhat robust provided you don't wire it up the wrong way round or give it too much current, both of which will kill it rapidly. Cheap. Fast. Available down to microscopic sizes. Some of the switched power will be lost in the transistor, causing it to heat up.

Transistor (FET): more efficient than bipolar, but also more fragile. Especially vulnerable to electrostatic discharge. Otherwise fairly similar, although voltage-operated rather than current-operated (so better for handling large currents).

Solid state relay: actually some transistors in a box. Supposedly the convenience and isolation of a relay with the speed and cycle lifetime of a transistor. Pricey.