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GCA131 Bipolar Relay Board Interface for Turnouts with single coil or motordrive


By Peter Giling

Some railroaders think, that GCA126 unit is a bit 'overdone'.

To satisfy also these critics, this unit is made. It only consists of 4 bipolar relays, and nothing else.

Loconet has a feature to program an output as a 'harware reset pulse'.

This means that the assigned output will only give a short (positive) pulse, which is long enough to activate the relay in a desired position.

The connected coil or motor will be switched permanently in positive or negative position, so these items should have an end switch in both positions.

This can be achieved with bipolair relays.

This relay will remain in its position as long as no other command is coming in, also after power-down and -up again.

In theory, it would be possible to use 8 simple and cheap relays instead of these bipolair types, but then there will be a lot of unexpected turnout movements at powering up Loconet.

An other problem that might occur, is that the pulse given by LocoNet hardware (GCA50) will be much shorter than the motor or coil might need.

Extension of this pulse by the software (read : Rocrail) is not desireable because that will seriously slow down the control program.

In any way, for slow movement turnout drives, it is much better to use MGV126 instead, particularly because of the feed-back.

If Rocrail does not have information about the real position of the turnout, accidents are about to happen.


GCA131 is only for situations, where a built-in end switch in both positions is available.

DO NOT use MGV131 without these end-switches.

If you omit this remark, fire hazard is possible!

Inductive parts like motors or coils give high power free-energy pulses when switched off, making a lot of distorsion.

This distorsion, if not suppressed correctly, is something that can cause many problems anywhere else in your digital system.

Due to the endswitch, it is not possible to suppress it on the MGV131 unit.

It should be built-in, straight to motor or coil.

The best way to do this is with a VDR resistor.

Simply connect the two wires of the VDR to the motor or valve connections.

Order number for fitting VDR : Reichelt VDR-0,25 30

Connection to GCA50 (J1)

The cable from this connector to the same on GCA50 board consists of 2 x PSK254/10G connectors with all pins wired 1 to 1, 2 to 2 , etc.

So NOT mirrored !

The hardware

^N.B. Self made pc-boards are not supported! ^

mgv131-en.txt · Last modified: 2018/11/12 08:56 (external edit)