CHAPTER 22 ■ SOLDERING AND CONNECTING
Building the Tube LED Circuit
The resistor and LEDs chain together in a column. Considering that, and the small number of parts, you can
solder the circuit together without a circuit board. See Figure 22-27 for an example.
Figure 22-27. Tube LED circuit implemented with three LEDs and a 150 W resistor soldered to a Molex KK
connector
Try to solder the LEDs facing different directions, so the light won’t be focused on a single spot within
the tube.
There is a possibility of the component leads accidentally touching each other in their scrunched-up
state within the tube. To avoid that, cover the exposed joints with heat-shrink tubing. At the very least, cover
the joint that connects the resistor to positive voltage. That way, even if a short circuit occurs down the line,
power must always pass through the resistor.
Finishing Up
Besides the main circuit board, only a couple of components remain to be completed. The 9 V battery snap
doesn’t require soldering, only a Molex connector needs be crimped on the end.
Obtaining the Power Switch
The power switch is as easy to prepare as the motor: Solder two wires, cover with heat-shrink tubing, add a
Molex connecter, and twist the wires together.
Because of the relatively low voltage and current consumed by the robot, almost any type of switch will
do. Most power switches are rated at several amps (A) and 125 VAC or 250 VAC. That’s more than rugged
enough to handle 0.5 A at 9 VDC.
If you want an illuminated power switch, be sure the built-in light’s voltage is appropriate for the robot.
If the voltage rating is too high, it’ll just waste the low-level DC power it receives without providing sufficient
light. If the voltage rating is too low, the bulb will pop. Maybe it’s better to avoid an illuminated power switch.
It’s worth selecting a switch in person rather than through a catalog so you can find one that looks cool and
feels good. Table 22-4 shows the part numbers of some power switches that fit nicely with Sandwich’s body.