Operant chamber power connections

Med Associates operant chambers use 28V devices. Output devices (e.g. pellet dispensers) are triggered by shorting the control line to ground; input devices (e.g. infrared beam detectors) short their report line to ground when they are triggered. All devices have a 3-way connector (the pin at the flat end is +28 V; the pin at the pointy end is 0 V; the centre pin is the data line).

In or about 2002, Med changed their wiring system. New boxes have a 25-way data connector and a heavy-duty 2-way power cable.

Pin on 25-way D connector on SG-716D2 panel attached to operant chamber	Corresponding SG-716D2 panel label (where devices are attached to the panel)	Old Med boxes used a different connection system, in which power was transmitted down the same 25-way cable as data:
1	OUT 1	OUT 1
2	OUT 3	OUT 3
3	OUT 5	OUT 5
4	OUT 7	OUT 7
5	OUT 9	OUT 9
6	OUT 11	OUT 11
7	OUT 13	OUT 13
8	OUT 15	OUT 15
9	IN 1	IN 1
10	IN 2	IN 2
11	IN 3	IN 3
12	IN 4	IN 4
13	IN 6	IN 6
14	IN 7	+28 V (power)
15	OUT 2	OUT 2
16	OUT 4	OUT 4
17	OUT 6	OUT 6
18	OUT 8	OUT 8
19	OUT 10	OUT 10
20	OUT 12	OUT 12
21	OUT 14	OUT 14
22	OUT 16	OUT 16
23	IN 8	+28 V (power)
24	(not connected)	0 V (ground)
25	IN 5	IN 5

Since we (at the University of Cambridge) already had custom boxes designed for the old Med systems with 25-way connectors, we had a choice of redesigning our boxes or rewiring the Med boxes. We chose to rewire the Med boxes for simplicity, even though this keeps the power going down the light-gauge 25-way cable. We achieved this using the following conversion: