Computer Automation Technology

Simple COR Buffer/Driver circuit

If you find that connecting a COR signal to a CAT controller loads the COR voltage, here is a simple Buffer/Driver circuit that should be helpful in most cases. If you have room inside of the DB25 connector that plugs into the CAT controller, this circuit can be built right inside of the DB25 connector. To proceed , follow these simple five steps:

Step 1
List of parts you'll need for this circuit.

Part Schematic ID Part Identification
RadioShack Part Number
Q1 NPN Transistor,   2N3904
R1 3.3K ohm 1/4 watt resistor
R3 10K ohm 1/4 watt resistor
R2 47K ohm 1/4 watt resistor

Step 2
Remove the DB25 male connector from your CAT controller. Unscrew the two "hold-together" screws to open the connector. See Figure 1.


Cor Fig1

Step 3
Carefully unsolder the wire connected to pin 6 of the connector. Refer to figure 2 for the correct pin location.

Cor Fig2 DB25 Male Connector viewing from pin side.

Step 4
Within the connector (or external if necessary) build the circuit following the schematic below:

Cor Fig3

Step 5
Carefully re-assemble the DB25 connector and reconnect to your CAT controller.


Please note: This transistor buffer inverts the COR signal so you'll need to set the COR polarity switch on the CAT controller appropriately.