GCA_LM2 (SPL Serial Programmable Leds)

By Fred Jansen and Peter Giling


This a very nice and cheap way to switch leds on and off, with a timing included in Rocrail.
Also a dedicated program is available to control the boards directly.
The board is connected to the serial (COM) port of the computer and controls 8 leds individual.
A protocol called SPL is used to control the leds, and also a special command is included to change address of this board.
The board can be connected into a chain of more than 50 boards, all with individul pre programmed address.
Supply of 5 V is needed, which should be adapted to total demand of power in the chain.
A nice supply unit for this could be GCA08-1 or GCA08-3.


The firmware is simple and could be dveloped in basic , using PicSimulator IDE form www.oshonsoft.com.

Basic sources and .HEX file

The hardware

The schematics
The pcboard and parts positions
N.B. Only complete ordered kits will be supported!


To give the user multiple choices of how to connect the board, there are several options.
Explanation and drawing are pending…….

The final result

A nice pc-board is available, in the same quality you are used to from GCA.

gca_lm2_pict01.jpeg gca_lm2_pict03.jpeg
The white connector can be used to connect to
GCA Interfaces like
GCA76, GCA77 , GCA107 etc.
GCA_LM2 ready for direct connection with leds
no resistors for leds needed.

Setup & Control

Connecting Leds (how to)

Stand alone controller

A standalone control program is available from www.modeldigitaal.nl

Connection LM 2 to PC.

One of the LM2 boards should be connected to PC as follows:

Connector J1 or J2
ComPort PC
- 5 Ground
S 3 Send, Tx

Connection between GCA-LM2 boards

Boards could be connected from one to another by using either J1/J2 or with the use of flatcable and J5.
In case J1/J2 just use 3 wires:
+ to +
s to s
- to -

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