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GCA51 LocoNet 2 x RFID + 8 input ports


Using the ID-12 or ID-20 RFID sensor, based on the idea of MERG, RFID in GCA units was first only possible with CAN-GC4, so for CBUS only.
Thanks to Rob, who opened the option to use it in RocNet as well.
But this ID-12 is a rather expensive solution, and also the used frequency of 125 kHz could be disturbed
too easy by the lokdecoder itself.
ID-12 together with one other sensor ID-20 were also pretty slow.
But for LocoNet® there was no solution yet
Thanks to the large amount of time that several enthusiastic Railroaders invested in this matter,
the use of the much cheaper and better RC522 came in view.
Special thanks to Viktor, Robert, Liviu and last but not least Gerard, we thank them this very nice solution.
As mentioned before, this RFID solution is based on the RC522 sensor, which is widely available for a good price.
Also the transponder to be fixed in or under the locs and, eventually, also under the waggons and pullmans, is very cheap.
The unit as described here is made for LocoNet specially.
It is based on a Atmega processor , and to make programming easy for almost anybody, without the need for
special programmers, the Atmel is traded for an Arduino Uno.
Now the Arduino Nano, if bought by yourself, can be programmed using the on board USB connection.
There is no need here for special programming devices.
See below under firmware.
GCA51 contains two inputs for RC522 sensor, and 8 x input ports like it's standard brother GCA50.
Also GCA51 has connections for standard RJ12 LocoNet® connectors, as wel as GCA-LocoNet® with the much more reliable SUB-D solution.
GCA51 can also be used for adapting between both connection options, but only for the LocoNet® communication.
Supply is not transferred between RJ12 connectors and SUB-D connectors,
due to the rather strange situation that Railsync in LocoNet® is used to supply the LocoNet® modules,
Railsync itself is yet transferred.
Rocrail is 100 % ready for RFID, so now you have a perfect system, capable of indicating each moving part on your railroad separately.
The transponders are passive in a way, that they do not need any power, which makes it specially easy for waggons.
The unit is made to fit in standard LTD-01 box.


The board needs 5 V supply. The total demand for the GCA51 when all I/O and RFID sensors are connected, exceeds easy 200- 300 mA.
This is a bit too much for a standard linear regulator like the good old 7805, since we have a supply form LocoNet or GCA LocoNet of 12V or even more.
It means that regulator should have a cooling for the 7 x 0,3 = 2,1 Watt.
Slowly the switching regulators are getting cheaper.
So the choice was now made to use a RECOM R-78E 5V type wich can easily handle 1 Amp, without any addional cooling at all.
This also means that the total consumption load from the LocoNet or GCA LNet supply is less than half, compared to a linear regulator.
But if you like to use the linear type with a cooling , it fits anyway and can replace the Recom.
The RC522 sensors need 3,3 V which is coming from the Arduino Nano unit.

GCA51 has two ways of connection:
- via GCA-LocoNet D-connectors
- via standard RJ12 connectors.
In both situations the power is connected between the two connectors (Railsync + / - in case of RJ12)
Between D-Connector and RJ12, only Ground and LocoNet signal is passed through.
This is done to avoid any railsync problems.
High speed diodes D1,D2 and D3 take care of that.

Connection Hall sensors

Hall sensors can be connected directly to GCA51 connectors H1..H8.
Ports 9 to 16 are available for that, which are also used for interface boards like GCA93,GCA94, GCA107 and many others.
The connection wires between Hallsensor and GCA51 can be up to approx 2 meters.
Please be careful not to feed those wires parallel with rails and rail wires.
If that is inevitable, keep a distance of 10cm (approx 4'').
Straight angle crossing is no problem.
A bit of twisting these wires (also the rail wires) will improve protection to any distortion.
Be sure to install RP1 and RP2 with a value of 4 x 470 Ohm each for best performance.
Below, a drawing is downloadable of how to connect hallsensors.

Connection TLE4905 hallsensor

Connection of driver boards

All driver boards for input and output like GCA76, GCA77, GCA93, GCA94, GCA107, GCA173 etc, can all be used to connect to J1.
Programming of the these I/O ports can be done in Rocrail using menue's Programming > GCA > GCA50
Ports 9 to 16 are available for that, which are also used for hall-sensor connection
Up until now, only pulse outputs are not supported.
Maybe in the short future, that will also be available.
We are still looking for somebody to take up that programming task.

Pull-up resistors for input signals.

If connector J1 is used for inputs like GCA93 and GCA94, it is better to use pull-resistors.
RP1 and RP2 are used for that.
A standard value of 1O KOhm is usually sufficient.
They are deliberately inserted in sockets, so they can be adapted in value for best performance, or removed when outputs are selected.
For hall-sensor use, these resistor arrays should be between 470 Ohm and 1 Kohm, to guarantee a
most reliable and distortion free functioning.

Schematic drawing and pcb


For Window users only! (as far as I know).
To make it simple for programming the Nano.
The zip file above also contains a GCA51.hex file.

PCBoard and Kit

Expecting end of april 2016

Possible connector setup.

Two main setup options are available in this unit.
These are all prototypes.!! Professional made pc-board are available now.

SUB-D male and female for GCA LocoNet and
1 x RJ12 for standard LocoNet
in LTD-01 box.
Same without the box 2x RJ12 for standard LocoNet compatibility
in LTD-01 box.

How to connect and use RC522 RFID sensor board

gca51-en.txt · Last modified: 2020/04/22 12:03 by phg