Elenco Electronics 202 - Manual (Page 83)

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Project #189
OBJECTIVE: To show that your body can be used as an
electronic component.
Build the circuit on the left. You’re probably wondering how it can work,
since one of the points on the NPN transistor (Q2) is unconnected. It
can’t, but there is another component that isn’t shown. That
component is you.
Touch points X & Y with your fingers. The LED (D1) may be dimly lit.
The problem is your fingers aren’t making good enough electrical
contact with the metal. Wet your fingers with water or saliva and touch
the points again. The LED should be very bright now. Think of this
circuit as a touch lamp since when you touch it the light emitting diode
lights. You may have seen such a lamp in the store or already have
one in your home.
Two-Finger Touch Lamp
Project #190
OBJECTIVE: To show you how finger touch lamps work.
The touch lamps you see in stores only need to be touched by one
finger to light, not two. So let’s see if we can improve the last circuit to
only need one finger. Build the new circuit, note that near point X there
is a 2-snap wire that is only mounted on one side, swing it so the
plastic touches point X. Wet a large area of one of your fingers and
touch it to both metal contacts at point X at the same time; the LED
(D2) lights. To make it easier for one finger to touch the two contacts,
touch lamps or other touch devices will have the metal contacts
interweaved as shown below and will also be more sensitive so that
you don’t have to wet your finger to make good contact.
One-Finger Touch Lamp