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1. CompuTrein Software
2  CompuTrein ISA outputcard
3. CompuTrein Bufferprint
CompuTrein Bufferprint
The buffer print buffers the 48 outputs from the ISA output card. The output card and the buffer print are connected with each other by means of a flat-cable. The buffer print uses a external power supply of 15Vdc/10A (like the 'Current Limiter' power supply elsewhere on this homepage).
The 48 outputs are separated into two groups:
  • 40 buffered with a transistor, capable of delivering 15V/1A.
  • 8 outputs with a relay, capable of switching 220Vac/1A.

All outputs statuses are visible by means of a LED located on the buffer print. The power supply is fused with a 8A fuse (NOTE: not all outputs can deliver the maximum output current at the same time).

Transistor outputs
The inputs A0..E7 are all connected to a PNP darlington transistor (T1..40). The emitter of T1..40 is connected to the +15V power supply trough two resistors R81..120 and R121..160. The collector is connected to connectors J3..J7 and to the LED D41..80. If the open-collector output of the ISA output card is open the inputs of the buffer print A0..E7 goes low. The Transistor T1..40 opens and a current will flow which lights the LED D41..80.
The transistor T41..80 limits the current which runs through T1..40. If the current get bigger than 1A the voltage over R81..120 and R121..160 gets bigger. T41..80 opens and T1..40 closes. In this way the current is limited to 1A. Because the darlington transistor can get hot, especially when the current limit function is active, they are mounted on a heat sink.

Relay outputs
The inputs F0..F7 are all connected to a transistor (T81..88). This transistor switches relay D81..88. If the open-collector outputs from the ISA output card are open the inputs F0..F7 are low (LED D81..88 light up). T81..88 opens and relay Re1..8 is activated. The contacts of the relay Re1..8 are connected to connector J8 and can be used for all devices that use a different voltage than 15Vdc (max 220Vac/1A).


Click on the schematic to view the full size

Part list
(without housing, heat sink, etc.):
  • R1..40: 10k
  • R41..80: 2k2
  • R81..120: 1,5
  • R121..160: 1,2
  • R161..208: 2k7
  • R209..216: 4k7
  • R217..224: 56
  • D1..40,81..88: 1N4148
  • D41..80,89..96: red LED 3mm
  • D97: BYW29
  • T1..40: BD678
  • T41..88: BC558
  • Re1..8: HB-2 12Vdc
  • C1: 100n
  • F1: 8At
  • J1: 50p flat-cable connector
  • J2: 2p power connector
  • J3..J7: 8p connector
  • J8: 16p connector
If you have any questions, suggestions or remarks on this description or on the schematic please send me an e-mail and I will try to respond.
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