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Bots / The Ultimate Palm Robot/ Mukhar & Johnson / 222880-6 / Chapter 9

238 The Ultimate Palm Robot

You can conceivably use the power and ground lines in J3 for multiple sen-
sors, but in general, you will find it easier to use the power and ground lines in
J4. While it does tie up an output port for each device, using J4 allows you to
give each sensor its own source of power. If you try to put multiple devices
onto the power and ground lines in block J3, you will need to attach your
devices serially or in parallel. When wired serially, the voltage drop across
each sensor will not be the full 5 volts supplied by the board. When wired in
parallel, each sensor will get the full voltage drop, but current will be reduced,
which could prevent the sensor from working properly. So you can see why
we prefer to give each sensor its own power line.
Using the power and ground pins from the output ports is exactly what we
did when we attached the rangers to the SV203 when building the PPRK
(Palm Pilot Robot Kit). Each ranger had a power and ground wire (the black
and red wires) that we connected to pins S6, S7, or S8. The yellow wire from
the ranger was the output wire. Each yellow wire was attached to one of the
pins in block J3.

When we attach any other sensor to the SV203, we will follow the same gen-
eral procedure. Power will be supplied to the sensor using one of the output
ports; input from the sensor will be read using one of the A/D ports. Remember,
though, if it makes sense for you, you can supply power to your sensor using
power from block J3.

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Monday, May 12, 2003 4:33:36 PM