Elenco Circuit Maker Sound Plus 200 - Manual (Page 40)

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Project #78
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 a 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 LED lights. You may have seen such
a lamp in the store or already have one in your home.
Two-Finger Touch Lamp
Project #79
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 (D1) 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
CM-200_Manual_031914.qxp_CM-200_Manual_031914 4/2/14 12:04 PM Page 40