Appendix E. Making a contact trigger
Here's one way to make a contact trigger. Begin by assembling the following supplies:
2 20-cm squares of stiff cardboard (1-2 mm thick)
2 20-cm squares of aluminum foil
1 20-cm square of black construction paper or poster board
Glue and tape
2 1-m wire leads
Now do the following:
- Smooth any wrinkles out of a 20-cm square of aluminum foil. Then glue the foil to the same size stiff cardboard. Tape the bare end of a 1-m wire lead to one corner of the foil.
- Smooth out another 20-cm square of aluminum foil and glue it to black poster board or construction paper of the same size. Tape another 1-m wire lead to a corner of this foil.
- From a second 20-cm square of stiff cardboard, cut out a 15-cm square hole, leaving a square frame of 2.5 cm width. Glue this frame onto the foil prepared in step 2).
- Arrange the various pieces as shown in the diagram. Notice that the cardboard frame acts as a spacer to separate the pieces of foil. If an object is dropped onto the upper piece, it will be forced into contact with the lower.