CHAPTER 23 ■ THE MOTHERBOARDCleaning the Board
Depending on the flux in the solder you used, it may need to be cleaned from the board. No-clean
flux and many of the newer rosin fluxes don’t require cleaning. Read the product label or check with
the manufacturer.
Specialty flux cleaning solutions are available if you really want to remove the flux.
Testing the Robot’s Electronics
When everything has been soldered, you may be tempted to immediately install a battery to see the fruits of
your labors. However, there are a couple of simple tests you should perform first that may save your battery
and circuit board from damage.
The Dangers of a Low-Resistance Circuit
If you accidentally soldered a positive wire to a negative wire, electricity would rush from the positive
terminal of the battery, through the shorted connection, to the negative terminal of the battery. The
remainder of the circuit won’t receive any current because electricity always takes the short path (direct
positive to negative). In that case, the robot won’t do anything.
It’s also possible to have a bad (or missing) part or partially shorted circuit, where one path in the
circuit has a very low resistance. In that case, a current-sensitive component, like an LED or chip, may not be
getting the protection it was supposed to be receiving from a resistor.
In any case, a shorted or very low resistance in a circuit consumes battery power quickly and generates
excessive heat. The heat is likely to damage components on the board, and finding the newly damaged parts
can be difficult.
Checking for Unsoldered Leads
Examine each part to ensure that it has been wired to something. A two-lead part with only one end hooked-
up indicates something is amiss. Every pin and every lead in Sandwich’s circuit should be connected to a bus
or another part.
Checking All Leads that Connect Directly to Positive Voltage
Electricity needs a path from the positive battery terminal to the negative battery terminal in order to flow. By
examining all the connections made to positive voltage, you can be sure that each of the paths starts out correctly.
Begin with the 9 V battery. Make sure that the red wire from the battery snap is hooked up to the
positive pin on the Molex connector. The positive pin on the Molex connector should be wired only to the
power switch connector. That is, power from the battery should not be allowed to enter the circuit unless it
first passes through the power switch.
■ Note When the power switch is off, absolutely no current can flow from the battery because nothing else
but the power switch is connected to the battery’s positive terminal. Therefore, the robot doesn’t consume any
power at all when the power switch is off. It’s as though the battery weren’t installed.
Even so, it’s a good idea to remove the battery if the robot is going to be stored for long periods of time. Aging
batteries can leak corrosive chemicals.