Simulation of Trackball circuit

[Danjovic]

The circuit on the link below (link) simulates the current integrator of the Trackball circuitry. The simulation provides some adjustments to be done like the Pokey POT lines threshold Voltage , Potentiometer Driving voltage (+CAV adjusted by R132). There is also a section with the potentiometer.

The trackball movement is simulated by a variable clock signal  (that should appear at TP7/TP8) and a direction signal that should appear at TP5/TP6).

One of the switches in the circuit allow the variable clock signal to rest at low state, which is the action performed by transistor Q1, commanded by CAV voltage line.

The other switch allows to switch the circuitry connected at pokey input to a potentiometer instead to the trackball circuitry.

 

The Pokey input follow the description of the datasheet. The dumping transistor is switched on at a frequency of 60 Hz (same as Vblank) with a duty cycle of 228 out of 262.5 lines (13%). 

 

 

Such simulation is useful to observe the behavior described in Field Service Manual, but the main reason I did that was to study alternative methods to activate the POT lines. 

 

 

 

 

[SoundGammon]

Dan Kramer, the "Trak-Ball" guy who designed the 5200 Trak-Ball, told me the Trak-Ball could be used as a digital input! He did not tell me how. I have a couple ideas as to how to make it work.

 

Take test points 5-6-7 & 8 which are each of the four directional inputs. Put 2 1K resistors and tie them end to end, where they meet connect to a test point. On 1 end of the resistors connect to 5V and the other end of the other resistor to ground. This will create a reference voltage at each test point. Now I want put a momentary switch going to each test point, like one in a joystick, and the other side of the switch to ground.