Rapid prototyping circuits like Arduino are a great resource when it comes to testing a design without having to worry about the setup of the base to test the design on. The same applies to the devices to be attached to Arduino itself : most of the times the I/Os are potentiometers, pushbuttons, LEDs, displays, IR emitters and receivers and sensors in general. And I don’t want to bother with soldering when the the source code (the ’sketch’) is there ready to run.

That’s why I developped and setup a few circuits ready to go with Arduino or general microcontroller based circuits : they come complete with wires, plugs to connect the Arduino and a few safety devices useful to protect the circuit and Arduino from possible wiring and programming errors. Connecting a switch in parallel to an output instead to an input might break the microcontroller or switching the three leads of a potentiometer might break it.

Many of my circuits are based on the original mini PCBs coming from consumer electronics, that’s why I never dispose or completely dismantle scrap TVs or printers on VCRs and all of the electronic devices I scavenge or get from friends (real friends ! ). I always save small PCBs with switches, motors and else together with the wiring and connectors.

The IR receiver in the picture above is on the original PCB froma Sony TV. The LED could be connected through an SMD transitor on the back of the pcb to the IR receiver to monitor the IR receiver output for received IR pulses.

The same for the IR emitter : a small LED on the collector of the transistor provides for a monitor of output IR pulses.

A better view of the schematic is here.

This is an example of protection device where the wiper of the potentiometer has a resistor in series : in case the wiring is switched and the wiper is incorrectly connected to a supply rail, the power supply is not shorted through the potentiometer burning the pot and possibly the power supply. Voltage drop across the resistor is not much of an issue as Arduino’s inputs leak very little current.

A capacitor at the wiper helps filter out wiper’s electric noise.

A better schematic is here.

The same for the pushbutton : however connected, no more than 5/220A (i.e. 20mA) are allowed to flow across the pushbutton (or an Arduino’s output pin). The board with the switches comes from an HP printer: as a bonus three LEDs are sitting there on the board along with the connector and wiring leads. The golden pins are from some PC board : heat shrink tubing helps keep the solder firm and lasting. This for male plugs.

Female sockets can be made easily with dismantled wire-to-PCB connector contacts and, again, heat shrink tubing.

On the left an RGB led with resistors (inside the heat shrink tubing. The piezo sensor on the right is a vibration/hit sensor. It doubles also as a piezo emitter. The schematic is here.