The goal of the device was to be at least 50% recycled materials and to cost no more then $5 per unit to make. As a side effect these devices can be mass produced for a larger distribution of the prank or to intensify it in one area.
The simplest idea that I came up with to meet these goals was to use a trashed solar garden light attached to a 3v piezo buzzer. When in the sun the device will produce a rather annoying buzz.
The solar cell from the garden light was removed and the housing and circuitry was retained for future use.
Before buying any additional part I did some research on how much power I had to work with.
Using my multimeter in voltage mode I recorded an open circuit voltage of 2.8v in moderate light and 3.5v in full light.
Then I switched the multimeter over to current mode and measured the short circuit current to be 50ma in moderate sun and 75ma in bright sun.
Step 1: Purchasing parts
The specifications met the power supplied of the solar cell.
Voltage rating 1.5-3V
Current Consumption 15mA MAX at 3V
These numbers indicate that I could run 3 of the buzzers in parallel simultaneously off of one cell.
1 buzzer consumes 15mA.
The solar cell provides 50mA in moderate sun.
50mA / 15mA = 3 and 1/3 buzzers.
To keep things simple I stuck to one buzzer per unit.
For mounting purposes, I found a piece of scrap wire on the street. You could substitute any sort of wire including coat hanger wire.
Overall the bill of materials include:
1 X Solar Cell salvaged from solar garden light
1 X Piezo Buzzer
1 X Scrap wire
Tools to build this project are
A soldering iron
A glue gun
possibly a multimeter