Parallax 28560 Manual page 9

Advanced Three-wire Connection
The Mouse Sensor includes circuitry to harvest its operating power from the clock line. This makes it
possible to interface to the Mouse Sensor with a three-wire servo-type extension cable. Because of the
Mouse Sensor's current requirements, however, some additional circuitry is required at the host end, as
described below. First, however, you will need to change the shunt configuration on the mouse sensor to
the following:
This connects the A input on the interface header to both the sensor chip's clock line and to the power-
harvesting circuitry.
BASIC Stamp 2 Family
Here's how to connect the BASIC Stamp for three-wire (servo cable) operation, using the additional parts
that come with the kit:
Using this circuit entails a change in the program, since the clock is now inverted from what it was. This
is easily accomplished by commenting out the line that says #DEFINE NEG_CLK:
'#DEFINE NEG_CLK 'Comment this out to use a the multiplexed clock and Vdd line.
You will notice that the program gives a much snappier performance with this setting, too. That's
because the sensor chip requires a negative-going clock. To provide such a clock, the PBASIC program
must resort to bit-banging the clock and data lines, which can be quite slow. But, with the above
circuitry, it can communicate with a positive-going clock, and that can be done with the much faster
SHIFTIN and SHIFTOUT instructions.
Propeller
The three-wire Propeller circuitry is a little more complicated than that of the BASIC Stamp. This is
because the Propeller outputs do not rise high enough to turn off a PNP transistor powered from +5V.
Therefore, an additional transistor is required to do the job. Here's the circuit:
Copyright © Parallax Inc. Mouse Sensor Kit (#28560) v1.0 6/1/2010 Page 9 of 18