Assembly and Testing

The first thing to do is take a magnifying glass and carefully inspect the PCB board for breaks and bridges. Below you can see some minor breaks in the pads. These will easily be bridged by solder during assembly. A break in a trace, however, needs to be specifically closed. If it's small, solder alone may suffice. Larger breaks may require a small piece of wire to be soldered across the gap. Bridges can usually be handled easily with a razor knife.

Use a continuity tester to verify that there is no connection between the ground and 5V buses (where the outer sockets go).

Etched PCB showing minor defect

When assembling the board I like to start with the voltage regulator. First I tin the three contacts on the board on which the regulator will sit. Next the three feet of the surface mount chip.

Surface mount chip ready to solder

Align the surface mount chip's feet onto the pads and, while pressing down, tack the chip in place with your soldering iron. From here it's a simple matter to secure the remaining feet.

Surface mount chip in place.

Next, add the remaining top side components. The two resistors provide a reference for the regulator and, depending on the specific values, provide a voltage from around 4.9 to 5.15 V. The electrolytic capacitors are specified at 10uF but I have lots of 22uF caps lying around so I use them instead. In a linear voltage regulator, a little too much capacitance won't hurt. The header for the voltage input is bent 90 degrees so that it will not bump into the PICkit2 programmer later on.

Note: When installing the electrolytic capacitors make sure to observe the polarity markings. The band (white in this case) denotes the -ve lead. Installing electrolytic capacitors backwards can make them explode (so I've been told).

Parts for voltage regulator

Note: Before populating the rest of the board it's worth testing the voltage regulator to verify that it puts out 5V. When you first apply power to the board, do so only momentarily. Check the regulator chip and resistors to make sure nothing is getting hot. If all seems well, apply power for a bit longer. If there's still no heat, power up the board and check that the output is near 5V. I tend to get between 5.0 and 5.15V due to variations in the resistor values.

Finally add the socket for the PIC chip and the bypass capacitor, the pullup resistor on the ~MCLR line (optional if you plan to program this line as I/O), and any sockets you choose to add. The sockets are optional. You can solder directly to the board, or install sockets where you expect they will be useful. The board shown below is fully populated.

Note: Before inserting the PIC chip, test for short circuits. This is most easily done while the PIC socket is empty. Set your voltmeter to continuity and test each pair of pins on the PIC socket. There should be NO connectivity between any of them. If there is, look for bridges between traces. Running a razor knife between the traces usually fixes these problems.

PIC board done

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