[[File:Atari-ST mouse adapter.gif]]
The schematic was released in german German magazine "Schneider Magazin, 07/1988", apparently using 5 diodes and a 4.5V battery.
Aside from Atari-ST mice, the circuit should also work for Amiga mice, which are basically the same, but with XA/XB/YA/YB connected to other pins, which could be resolved at software side (or at hardware side).
CPC Joy Port Atari-ST Mouse Amiga Mouse
Batt4.5V (+) ------------------ Pin7 +5V Pin7 +5V
=== CPC Plus Compatibility === The low-level XA/XB/YA/YB signal must be watched by software (the 300Hz interrupt is probably too slow to sense fast motions, so therecircuit reportedly doesn's little chance to have t work on CPC Plus computers. There are additional diodes in the mouse driver running CPC Plus which do cause problems in background)this case.
== Timings ==
The Atari/Amiga mice do output low-level signals, directly coming from the motion sensors. Ideally, software should check the signals ''more than 500 times per second''. FutureOS does that, but not the firmware. Using the CPCs 300Hz interrupt to check the signals might be a bit slow; it would work, but may miss some signals when the mouse if is moved too fast.
Reading the mouse more often than 300 times per second would be better, but it'd require more CPU load since it can't be done via interrupts. Possibly best solution would be combination of IRQ and non-IRQ handling: Always check the mouse on 300Hz interrupts, and - if the program isn't busy with other tasks - additionally check it via polling.
XB _____-------------------------------____
In the above case, checking only raising XA would miss the direction change on falling XA (if that happens repeatedly, then the mouse would disappear towards the screen border, eg. if the mouse is in an unstable position, without actually being moved).
== CPC Plus Compatibility ==
The circuit reportedly doesn't work on CPC Plus computers. Probably simply because of the missing Fire3 signal on the joystick port of the CPC Plus. There are also additional diodes in the CPC Plus, which may drop the voltages a little, but probably do not cause problems in this case.
== Software supporting the ST-Mouse ==
* [[G-Paint]] 2.0 (Günter Radestock)
* [[FutureOS]]
* [[G-Paint]] 2.0 (Günter Radestock)
[[Category:HardwareDIY]] [[Category:PeripheralsFutureOS]] [[Category:DIYInput Device]] [[Category:Peripherals]]