CHAPTER 23 ■ THE MOTHERBOARD
Your meter may give slightly different readings, but there should be a noticeable change from the
robot’s power off switch position. In diode test mode with the switch in the on position, anything above 1.6 V
or below 0.4 V is suspect.
Reheating Solder Joints
If at some point during testing you discover a weak or loose solder joint, it might be worth briefly reheating
all of the solder joints on the board to ensure they’re completely bonded. You probably don’t need any more
solder, just touch the soldering iron tip to each joint until it melts completely. That should cause the solder
to flow through and coat the joint.
Unlike wire stripping, wire attachment, and soldering, the reheating process is fairly quick. Five minutes
spent guaranteeing clean joints saves a lot of frustration in debugging.
■ Caution Never solder or reheat joints when a circuit is powered on. The combination of heat from the
soldering iron and heat generated by electrical flow permanently melts apart the tiny bonds and leads within
semiconductor component cases. Also, brief short circuits can result from the edge of a molten solder blob
accidentally contacting multiple traces, leads, or wires.
Holding Your Breath
After the multimeter tests verify an acceptable resistance and voltage drop, it is finally time to connect the
battery to the line-following circuit board. The power switch is in the off position, isn’t it?
Power up and chant the mad scientist’s creed, “It’s alive! It’s alive!”
If everything went well, you should be rewarded with a soldered circuit that performs as well as
the circuit on the solderless breadboard. If not, follow the paths on the modules that aren’t working. Is
a component in backwards? Is a nasty solder joint spilling onto other wires or leads? Do the voltages at
each point in each module on the soldered circuit match the voltages at each point in each module on the
solderless breadboard?
The robot is nearing completion. All that remains is to build a body to protect the electronic guts and
hold it all together.