Interface for Tandy Joystick - Vectrex ====================================== +5V +5V J5 )--------+--+---------+--------------------------------------------( V7 | | | Gy | \ 10k | | / | 10k | \ +----)---/\/\---+ | / | | | | | | |\| | | +----+--|-\ | Pot0 X | | >---------+---------------------------------( V5 J1 )--------)----------|+/ U1a Gn | |/ 1458 / \ 10k 100k / +----/\/\----+ \ | | | | | Y 47k | | |\ | J2 )--/\/\/-)------+---|-\ | Pot1 | | >-----+-------------------------------------( V6 +----------|+/ U1b Bu | |/| 1458 | | -5V / +--------------------------------------------( V9 \ 4k7 W / \ Gnd | 0V J3 )--------+------------------------------+-------------+------------( V8 | | Bk | | SW2 | -+ SW1 | -+ =| =| | -+ | -+ | | Sw1 | +------------( V1 | Br | | Sw2 +--------------------------( V2 R SwA Sw4 J4 )------------------------------------------------------------------( V4 Y SwB Sw3 J6 )------------------------------------------------------------------( V3 Or 6 pin DIN skt 9 pin D skt Theory ------ The switches are simple : The Tandy joystick has 2 fire buttons which ground the appropriate pins (4 and 6) on the connector when they are pressed. Thus, these pins are simply linked to the button 4 and 3 (respectively) inputs on the Vectrex. Two more buttons on the interface (SW1 and SW2) ground the remaining 2 Vectrex inputs. Although the Tnady joystick is proportional, it differs from the Vectrex unit in 2 important ways. a) The output voltage varies from 0 to +5V, not -5V to +5V b) The Tandy joystick output increases for movement to the right and movement down. The Vectrex joystick output increases for movement to the right and movement down. The conversion between these 2 systems is performed by U1, a 1458 Dual Op-Amp. U1a, wired as a non-inverting *2 amplifer, doubles the X voltage without reversing it. The input resistor is returned to the +5V line to provide the required voltage offset. U1b is wired as an inverting amplifier with a gain of approximately 2, which inverts and doubles the 'Y' voltage. The potential divider connected to the non-inverting input of this device provides the necessary offset. Notes ----- 1) Layout is not critical, and any standard technique should work 2) The Op-Amp used was a 1458. Any similar dual Op-Amp should work, but has not been tested. 3) Connection to the Vectrex is best performed by using the socket end of a Sega extension lead. The colours on the circuit diagram are the colours in the cable used for the original design. 4) Connection to the Joystick is perfomed by a 6-pin DIN socket 5) 2 more swtiches (SW1 and SW2) provide the extra 2 vectrex buttons. 6) Distribution and use of this circuit for the benefit of Vectrex owners is encouraged. Please feel free to put it on ftp sites, etc.