Electronics Lab

Published September 20, 2017

For week two of Physical Computing, we are doing a lab on basic electronics: soldering and switches.

I wanted to find a way to use a mini joystick from the electronics store in this lab.  The joystick has three possible movements:

  • forwards / backwards

  • right / left

  • pushbutton click

My first task was to discover exactly how each of these movements translated into an electronic signal.  On inspection, each of these movements had a separate set of pinouts.  Forwards / backwards and right / left had three pins each.  Using a multimeter to measure resistance, it became clear that the center pin was common, and the pins to either side corresponded to the movement in that direction.   The pushbutton click had four pins, but after measuring for continuity, it became clear that two sets of two pins were connected electrically.

 

I drew up the electrical connections in a (decidedly not standard) schematic-ish:

So, now I got to soldering.  First, I stripped my wires (which already had pin headers on one end), tinned them, and soldered up the sw

 

And hooked the four potentiometers (left, right, forward, backward) to four LEDs in line with a resistor:

Questions:

  • When measured with the joystick in the central position, the resistance between the center pins and each of the four directional pins is above the level the multimeter can measure (200M Ohms).  I assumed this was an open circuit.  The resistance when the joystick is pushed entirely in one direction is less than 20 Ohms.  However, when everything is connected up, the LEDs are lit (although dim).  I have two theories for why this might be:

    • I am misusing the joystick, which is perhaps meant to act as a control (with resistance measured by an Arduino or similar and mapped to a value in a piece of software) rather than actually pass current through it.

    • LED cathodes are connected on the +5V center rail, and the anode is connected to ground through the joystick.  Perhaps the anode end is at a different ground than the ground of the circuit… but that still leaves an open circuit with a LED lit…

  • I attached a number of LEDs in parallel to the pushbutton function on the joystick. Only some of them light up when pressed.  If I have (1) red and (2) blue LEDs, only the red will light up (which, I assume is due to lower resistance) until the red  is pulled and both blue LEDs light up.  What is the limiting factor here?  Is it the current put out by the power supply?  How would I light up all three LEDs?