Older type feeders from RV1 (?and RV placer?) need a mod to work with the RV1s and RV4s.
The older feeders need a +/-12V supply for their RS232 driver. A small DC/DC converter to supply This can either be added to the main RV control box to supply all feeders, or to individual feeders. The former option needs a converter capable of supplying enough current to run as many old type feedes as are likely to be connected - I've not measured the current draw, but 20mA per feeder should be fine based on the sn75188 datasheet.
To mod a single feeder :
Get a small +5 to +/-12V DC/DC converter. Original feeders use a Traco unit but I used a cheaper
Recom RD-0512D from Rapid.
Connect wires for the 0V and +5V feed to the converter - 0v to pin 4 of the SN75188, +5v from the + side of the nearby capacitor.
Cut the red and black wires between the control board and the rear connectors, and connect the board ends to the +12 and -12 outpust of the conevrter respectively. If using an isolated converter like the Recom, remember to link the 0V to the input and output pins of the converter.
For the Recom, the connections are :
Pin 1 : +5V from control board
Pin 2 : 0V from control board
Pin 4 : -12V : black wire
Pin 5 : 0V
Pin 6 : +12V : red wire
To add a converter to the control box You'll need to find a suitable supply to feed the converter - I've not looked into this but there is bound to be a +5 or +12V supply in there somewhere - just pick a converter with the right input voltage. You will need to get some crimp pins for the connector - RS and Farnell do these connectors.
Pin 3 is -12V, and pin 6 is +12V.
