The analog and digital pins route through JP1 and JP2. If you wish, you can cut the traces between the
sections of JP1 (digital) or JP2 (analog) and reroute the signals. For example, you might put a series
resistor between the holes to limit current. Or you could route a wire from an analog input to an op-amp
in the spare IC4 socket and then back from the op-amp to the GP3's CPU. Note that on JP2, the 5th pin
(near J1's A3) is not connected through and only connects to an unused GP3 pin.
IC4 is available for use with any circuitry you might want to add unless you are using it for the USB
daughter board. An op amp, a temperature sensor, a solid state relay, a DIP switch, or anything else you
can arrange to fit in an 8 pin DIP factor can be placed at IC4. The IC4A and IC4B holes connect to IC4
to provide places you can connect your circuitry to the board. In addition, there are convenient holes that
carry +5V and ground nearby for your use.
The LED output is brought out to JP1 and also to D1A which normally takes a 5V LED. You can also fit
D1B as a normal LED with an appropriate dropping resistor at R2. It is possible to use both LEDs if the
output current of the GP3 pin is not exceeded (in which case both LEDs will light or extinguish
together). Another option is to install a 5V LED at D1B and omit R1. Then you can use the R1 pad with
the circle around it as a connection point. For example, you might wire from the circle pad of R1 to one
of the JP1 digital connections to get a second LED output. It is not necessary to install either D1A or
D1B for the GP3's operation.
Once you have decided on the options you wish to use, you can assemble the board. In general it is best to start
with the “low” components first. IC1's socket and IC2, for example are easiest to install first. Then you can
install discrete components like the smaller capacitors, resistors, and LEDs. Large components like the
connectors, C6, and IC3 should be installed last.
Construction Notes
•
If your kit is supplied with two 24 pin .1 inch headers simply remove every other pin with pliers so
that the headers fit in the J1 and J2 slots.
•
C1-C4 have polarity markings but it is not necessary to use electrolytic capacitors. If your kit is
supplied with ceramic capacitors for C1-C4 you can ignore the polarity markings on the board.
•
C6, the LEDs, and the ICs are the only devices that you have to be careful to observe the orientation
marked on the board. C6 should have its + or – lead clearly marked and the + side is marked on the
board. The longer lead of LEDs will go in the hole marked with the plus sign.
•
IC1 and IC2 should be oriented as shown on the silk screen. The silk screen for IC3 shows a thick
bar near the edge which is the back of the package (the side without the part markings).
•
Because IC4 is uncommitted you can install something in IC4 any way you like (including on the
back side of the board) as long as you do the rest of the wiring to IC4 to match.
•
Although it is customary to put the body of the resistors in the hole that has the white circle around
it, putting one in backwards will not affect circuit operation.
•
Although it is customary to put the ceramic resonator or crystal so that the markings face away from
IC1, putting it backwards will not affect circuit operation.
•
Don't forget that JP1, JP2, IC4A, IC4B, and DTEDCE all have traces connecting pins “across” from
each other. If you are making any modifications that require these holes to be electrically separate
you must use a hobby knife or razor to carefully cut through the trace on the top side of the board
that connects them. You should check that you have made the cut by using an ohm meter before and
after the cut. Of course, be careful not to cut other parts of the board.
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