User Manual

33
EXPERIMENT #21: THE ONE FINGER TOUCH LAMP
Actually, 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. Connect the circuit, the only changes from the last experiment are the
addition of the 1kΩ and 10kΩ resistors. These two resistors plug into adjacent (but not connected) holes g10 and g11.
Wet a large area of one of your fingers and touch it to the resistor metal coming out of these two holes at the same time;
the LED 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.
This circuit is still different from the touch lamps sold in stores because the LED goes dark if you remove your finger from
it. We need a way of remembering when you’ve touched the lamp to turn it on or off - we need a memory, and we’ll show
you one in Experiment 45
.
+9V
3.3kΩ
10kΩ
470Ω
1kΩ
BATTERY
CONNECTION
TRANSISTOR
CONNECTION