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GCA126 Interface with feed-back for motor powered turnouts


By Peter Giling

Features and facts

4 individual outputs

600 mA max load per output.

Max 42 Volt per output.

4 individual inputs.

4 corresponding outputs for feed-back.

Time selection for output duration.

Outputs are activated one by one for power reduction.


Controlling a LGB 1201, Kato or Fulgurex turnout-drive, in fact also some type of Hoffmann turnout motors, only have one coil or motor, that needs to be controlled by polarity.

The normal driver interfaces, like GCA76 or GCA77 are not suitable for that.

The complexity of this unit is slightly higher.

In the GCA units, it is standard, to separate the power, needed to activate the coils and the LocoNet system by means of optocouplers.

This unit is able to control 4 turnouts, and needs 4 inputs from the MGV50.

It also provides 4 feed-backs, to indicate that motor has reached new position.

So 2 units, capable of a total of 8 turnouts, are commanded by 1 MGV50.

It is also possible to make a pushbutton or switch control for direct activation without GCA50.

The software in the PIC16F62x is made in such a way that the processor provides a correct timing for the coil or motor, and switch it off after the set time with SW1.

This will take care that the turnout coil will not be overheated by too long powering.

An I2C expander provides to extra i/o pins to the processor.

This unit is specially useful if you have turnout drives with defective end-switches

These switches can be shirt circuited and/or removed if using this interface..


The power ouputs on GCA126 have built-in suppression diodes, to suppress high-energy pulses at the moment the output is switched off.

If the turnout drive contains end-witches, there are two possible options.

1) the endswitches should be removed or short-circuited, even when they are in good health.


2) a VDR 30V (Reichelt VDR-0,25 30) should be mounted directly on the connections of coil/motor.

Cable to MGV50 / CAN-GC2

Time delay settings

SW1 is used to set the delay time after which the feed-back will be activated and the output switched off.

Delay table
Delay in Sec SW1 1 SW 2 SW 3
0.1 Off Off Off
0.2 Off Off On
0.4 Off On Off
0.8 Off On On
1.6 On Off Off
3.2 On Off On
6.4 On On Off
12.8 On On On

The hardware

The firmware

So far, the unit is only theory, because it was designed for someone.

I made a prototype printed circuit, but have not recieved any fee-back on the result….

mgv126-en.txt · Last modified: 2018/11/12 08:56 by