The other way around, also on three legs

A pushbutton for the ARDUINO needs three wires, this is for an input. The output, steering something from the ARDUINO has (no wonder) also three legs, it can be done by a transistor:

The middle wire of a transistor is the boss. When it has the proper signal (depending on type of the transistor , HIGH or LOW) it lets current pass through the outer two legs:

The port can have a 4.7K Ohm resistor, the effect only depends on the HIGH or LOW!

Cees Baarda provided with a transistor type: BC547C, others can be used too.

This way you can switch on or off: LED’s, speakers, etc. For more complex things to switch on, being on higher voltage than the ARDUINO, or if you want to save the power of the ARDUINO (using it stand alone, not on USB) and the thing to switch on has its own power, then you use a relay (relais).

A relay has two circuits, one to switch it (on low voltage) and the other (independant) with the real voltage, which can be much higher. The small voltage switches the high voltage circuit. Here is the picture from the datasheet from a relay:

You see legs 1 and 10 are the low voltage steering pins, and both sides have a high voltage switch between pins 7 and 8 (3 and 4).

So you can use the transistor to drive the relais, and the relais to switch on heavy duty things! Here the drawing of Cees Baarda, tested!

From this relay the High Voltage of EL wire, or EL sheet can be switched of and on, regulated by the ARDUINO. The relais makes a sound (the magnetic jumper like a ticking “cloque de coucou”

PS there is one more: the diode protecting the input port…..but it all very do it yourselfable.

PSS what does this cost? - where to get it?

relatively cheap: transistor BC547c conrad.nl 0,13 euro

resistors (koolfilmweerstand) conrad.nl 0.09 euro

relay (relais) conrad.nl 1.69 euro

diode conrad.nl 0.04 euro