You’ll need:

• A two cell AA or AAA battery holder
• A 47 Ohm resistor and LED
• A LM358 Op-Amp
• A 10K Potentiometer
• A soldering iron and some glue

Distance sensors are pretty expensive ranging between R200 and R300 each, but the two I bought have found themselves in more projects than I care to count (you only need one for this project). I’ll be using the LV-EZ0 which can be picked up locally at www.netram.co.za. You can find all the rest of the parts at your local electronics store for under R20 or or buy them online from www.communica.co.za.
The 8 pin Op-Amp has a little notch on one side. Hold it with the pins pointing down and the notch at the top. The pins are numbered anticlockwise starting with pin 1 at the top left (ending with pin 8 at the top right). Connect pin 8 to the red wire of your battery holder, and pin 4 to the black one. Also connect the longer leg of your LED to the red wire and the other leg to the resistor. Connect the other leg of the resistor to pin 1 of the Op-Amp.

Connect one outer pin of the Potentiometer to the red wire and the other outer pin to the black one, the remaining center pin is connected to pin 2 of the Op-Amp. Finally connect the pin labelled “+5” on the sensor to the red wire, “GND” to the black one and “AN” to pin 3 of the Op-Amp. I simply glued all the components together and soldered the connections in place.

To install the unit, stick it to the front wall of your garage while your car is inside, now slowly turn the screw on the Potentiometer till the LED just turns on. If your car moves further away the LED will turn off giving you an indication of how far you are from the wall.

In fairness you could always just stick with hanging a rubber ball from the ceiling but this isn’t nearly as interesting. [MS]