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Mouse Or Joystick Switch For Amiga Schematic Circuit Diagram

Simplifying Input Device Management

Mouse or joystick switch for Amiga: For Amiga enthusiasts who find it cumbersome to disconnect the mouse each time a second joystick is needed for gaming, an intriguing solution lies in this circuit. This all-electronic switch is designed to be seamlessly connected to the joystick-1 port on the Amiga, providing a hassle-free experience. Constructed with minimal components, the circuit operates effortlessly, automatically detecting whether the joystick or mouse is in use. The Amiga’s mouse, which provides four signals alongside the two button signals, forms the basis of this clever circuit. Signals H and HQ (or V and VQ) indicate the direction, while X0 and X1 convey the speed (refer to Fig. 2).

Joystick and Mouse Activity Detection: Streamlining Input Signal Processing

Both joysticks provide similar signals, although it’s important to note that detecting joystick activity is a more straightforward task than discerning mouse activity. Joystick activity is identified when any of the four-direction signals go low. In contrast, mouse activity detection involves comparing the current state of the H and V lines with the previous state. The mouse is considered active when these states differ. Typically, implementing an activity detector would require a bistable and a clock. However, a more straightforward solution has been devised by leveraging the propagation delay of the logic functions embedded in the GAL.

The actual delay is not critical in practice, making even the slowest GALs suitable—mere nanoseconds prove sufficient for a reliable mouse activity detector. To combine signals from the left-hand mouse button and the joystick button, diode D1 is employed. Pull-up resistors are incorporated with the joystick and mouse inputs to prevent undefined signals when either device is not connected. For those with access to a GAL programmer, the source listing can be utilized.

Mouse or joystick switch for Amiga Schematic diagram

*IDENTIFICATION
ELEKTOR ;
*TYPIC GAL1 6V8 ;
*PINS
M1=2,   M2=3,  M3=4,  M4=5,  J1=9 ,   J2=8,    J3=7,
J4= 6, Q2 . T=12, Q3 . T=13  Q4 . T=14
HOUT . T=15, VOUT . T=16, SWM . T=17, DIF . T=18,
Q1 . T=19
*BOOLEAN EQUATIONS
SWM = /DIF & SWM & J1 & J2 & J3 & J4
+ DIF;
Q1 =  SWM & M1
+ / SWM & J1;
Q2 =  SWM & M2
+ / SWM & J2;
Q3 =  SWM & M3
+ / SWM & J3;
Q4 =  SWM & M4
+ / SWM & J4;
VOUT = M1;
HOUT = M2;
DIF =  /VOUT & M1
+ /M1 & VOUT
+ /HOUT & M2
+ /M2 & HOUT;
*END

Mouse or joystick switch for Amiga Schematic diagram
Fig. 3 to produce a JEDEC file and program their own device. If you do not’ have a GAL programmer, you may like to know that IC1 is available ready-programmed from Elektor Electronics (publishing).

Parts list

Resistors:
  • RI = array, 8×3.3 kΩ
Semiconductors:
  • Di = 1N4148
Integrated circuits:
  • ICI = GAL 16V8 (ESS6003)
Miscellaneous:
  • K1, K2 = 9-way male sub-D connector, angled, for PCB mounting
  • K3 = 9-way, female sub-D connector, angled, for PCB mounting
  • PCB Ref. 914078

Mouse or joystick switch for Amiga Schematic diagram

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