With this information in hand, find the variables (in parns. above) in the
top area of the postscript file and edit them. Also set the radius of the
wheel you would like (wr).
This should make a wheel compatible with the expectations of the optical
readers. Notice also the orientation of the wheel slots to the chips, this
must be keep the same.
Note that the parts in the mouse will only allow for the A and the B
channels, for the index channel an opto-interrupter must also be added.
Now to the circuit, for this example it will be assumed that the power used
is +5V DC, thus there are 5 connections, ground, +5v, A, B, and index.
There will probably be two LEDs used, one for the channel A/B reader, and
one for the index. As these LEDs have about a 1.1 volt drop, they can be
put in series, along with a resistor of about 47 ohms, all across the 5
Now for the readers, they seem to come in two flavors:
- Simple dual NPN transistors with a common emitter connection and
open collectors, no base leads. These will have 3 leads.
These could also be FETs.
These will require pull-up resistors on the collector leads, to +5
volts. Some 4.7k resistors should work fine, the exact value is not
real important as long as they do not go below about 500 ohm.
Take the output from the collector leads, this will give a TTL
- More sophisticated devices with four leads, these do NOT require
pull up resistors, as they are NOT open collector. These chips may
do some processing to cleanup the signals. The pin outs of the
ones I've seen are (as looking at the front) channel A, +5 volt,
ground, channel B. The output from these chips is likely TTL
For the index, use a stand alone interrupter module, which is likely open
collector and will need a pull up resistor as above.
These signals can now drive the input lines of a parallel port to get the
signals onto a computer. EMC may help