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• The GCA modules

Probably all modelrailroad clubs are struggling with this delemma:
How can we safely switch from one system tot another on the test layout, without troubling
with connectors, screw terminals, loose wires, etc.?
We were facing the same problem and since we would like to install a new table for testing loks,
I created this GCA207 / GCA208 combination.
The picture on the right hand side whows the result, satisfying anybody in our club who has something to do with maintenance and decoder assembling.

So far we had these option on our wish list:

• ESU DCC programming unit, with a testboard for decoder connection.
• Marklin Gleisbox with Mobile Station 2
• Sprog 3 for use with JMRI
• External connection for anyone who would like to bring his/her own central station
• Marklin's old fashion tranformer
• dc current transformer.

Futher more on this table needed:

• a computer so we could install:
  • Rocrail by default
  • ESU Lokpilot program, so we could program sound decoders.
  • JMRI program for use with Sprog (very few people want a different choice from Rocrail.

(understandable, but I just like to keep everybody happy)

• roller bar
• a few rails in different scale
• a switch to change rollerbank and K-rail between two and three rail function.

Well, that demanded many connections, wires, screw terminals, whatever, with always the serious risk
that somebody was making a mistake, with or without purpose.
So I made unit GCA208 and a control panel GCA207.
The boards belong to each other.
All rails are connected together, except roller bar and K-rail which have a separate 3-wire connection.
There are a total of 7 push buttons for selection of various tasks.
All central station and transformers are connected to the relay board, and will,be swiched
in such way, that there is no possibility to connect two or more central stations/boosters/transformers together.
That was the first and major task for this relay board.
6 buttons are for selection of various functions, and 1 button for selection between 2- and 3rail.
The relays are all Double Pole Double Task type ORON G2R 24 V coil.
This assures that relays can easily handle the maximum currents of anything that is connected.
The total system is also provided with a dc controller (with incremental switch, no potentimeter!).
Controller adjusts the dc output (if selected) between 2 and 16 Volt,
very convenient for checking motors of locs. before a new decoder is connected.
Futher more, a volt and amp meter is integrated in the system, which makes testing of motors very convenient.

To avoid a lot of wires between front and relayboard, connection is made via I2C, so only for 4 wires are needed
for all teds, incremental and push buttons.
The relay board contains a microprocessor with is taking care for all decisions, and also makes it impossible to activate two selections at the same time.
Control of dc output to rails is done by a PWM output from processor, but this PWM is filtered before it reaches the regulator, so there will be no ripple on dc output.
This is important because some decoders can be damaged by PWM power, or at least show some unexpected reactions
Since this regulator is not able to produce less thee 1,25V, the processor will switch dc off when regulator is set below 2V.

All boards and/ or complete kits are available if there is any interest
Just ask Peter