[GreenKeys] Range and Bias

[Jeffrey D Angus]

All in all the operation of the selector magnet and the range finder is an
absolute marvel when you come to think about what it really does.

It begins with the start pulse. The selector lets go and trips the clutch
to start the "lets go and see what happens during one revolution."

The combined mechanical levers, clutch and rotating shaft are in effect,
just a 5 bit serial in parallel out shift register.

As the shaft rotates, it takes a sample of what condition the selector
magnet is in. This "look" is only about 1-2 mS long. The equivalent
electronic analogy would be "sample and hold" or in the case of a
digital shift register, the clock signal that loads each sequential bit.

Normally, the "look" is down at 33 mS after the the start pulse leading
edge. That would put it right in the middle of the first data bit. Then the
next 4 "looks" are done every 22 mS.

Depending on the amount of distortion, meaning the mark to space or
space to mark transitions not being where they should be, the range
finder will allow you to move the "look" slightly before or after the
middle of the data bit to correct for the transitional errors.

As the shaft continues to rotate, after the 5th data bit is "stored" the
machine "strobes" the register and outputs the data. By printing or
doing one of the other functions.

The reason for the extra 1/2 width stop pulse it to give the machine
time to settle in case it's not quite running at the correct speed.

Then it waits for the next start pulse to go through the entire sequence
again.

The ranger finder does not change the sampling interval. That is fixed
by the machine speed. But it does skew it one way or the other time
wise to help deal with transitional errors.

Jeff-1.0
wa6fwi