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GCA-PI04 RocMouse.


Discontinued, due to unavailability of chip PCF8591 in DIL16.



The RocMouse is a hardware throttle which can be connected to the GCA-Pi0x.
RocNetNode send the throttle commands direct to the Rocrail server so the throttle will be Command Station independent.
Assigning a loco to a throttle is done with the dispatch command.
There is furthermore not much to explain about this unit.
No microprocessor is needed, since all intelligence is handled by Rocnet. Just one 8 bit I2C expander and 1 A/D I2C converter is used.
Like GCA-PI02 and GCA-PI03, this unit also contains a line driver, to enable longer wiring.
The used potentiometer is a cheap standard type pot with 6 mm axle.
It will be suitable for all circumstances.
There is however room on board to replace it with the much more expensive sealed types.
To achieve a more stable reading from the speed selector, an extra 3,3V stabilizer IC5 is added.
Also, to avoid reaction on the speed while pushing S6 or the reverse switch, these switches have additional zener diodes.
This all together results in a very nice hand held throttle, and very easy to assemble yourself.

Professional Boards/Kits

Factory made boards and Kits are available:


  • Rotary knob for speed; 50 steps which are recalculated to meet the real loco speed steps.
  • Direction switch with V=0 position.
  • 28 functions divided in groups of 4. The group number is represented as binary number by the LEDs above1) the buttons.
  • Lights.
  • Flashing Scan/Run LED.
  • Up to 8 connected with one RocNetNode.

RocMouse als kit

gca_pi04_pict09.jpg gca_pi04_pict10.jpg

In this testkit, a professional Potentiometer is installed, which is in different position assembled as a normal -in package- potmeter.


  • P82B715 I2C line driver.
  • PCF8574A I2C I/O extender.
  • PCF8591 I2C ADC.


The schematics
The pcboard with parts positions
The bill of materials
Grber files
N.B. Only complete ordered kits will be supported!

Assembling instructions

A few remarks have to be made to help you being succesfull with the production of this RocMouse.
Fix the empty PCB with fasteners in it's future housing, and use it to drill the exact positions of the pushbuttons, SW1 and leds.

Use the pcb as a mould for holes of 6 pushbuttons, 4 leds and SW1. and Potmeter
Pushbutton positions and leds have a little center hole for this purpose.
All other parts can be mounted after that.
The pushbuttons and leds are mounted at the backside of the PCB.
Please take care not to use the center hole of the leds, because that one is only a drilling mould.

One other remark on mounting RP1.

This 6 pin resistor array has one common point, indicated with small stripe or dot.
This indication should be at the side where text 'RP1' is marked.


If Rocnet is not the first Command Station in the list de Dispatch IID must be set: DP IID
Linking a RocMouse with a loco is done in two steps:

  1. Use any functionality of the Rocmouse to link it.

Operating instructions

Run LED Direction switch
Speed rotary
Function group LEDs
F1 F2
F3 F4
FG Lights


It flashes fast in case no loco address is assigned to this RocMouse.
After a dispatch and any command from the RocMouse it will flash slowly.

Direction switch

The direction switch has three positions:

  1. Left: Loco direction reverse.
  2. Middle: Loco speed set to zero and a release is possible with both FG and Lights pressed.
  3. Right: Loco direction forwards.

Speed rotary

Loco speed control in 50 steps.

Function group LEDs

Show the actual function group in binary form.


Flip functions in the selected group.


Function group selection button: 0…6.


Lights button.


GCA_PI04 needs adressing.
Max 8 RocMouses can be connected to one Raspberri Pi.
Adressing should be made on positions at the back side of IC2 and IC3.
It is established by soldering the center point with a or b, according following list.

RocMouse IC2 and IC3
1 1a 2a 3a
2 1b 2a 3a
3 1a 2b 3a
4 1b 2b 3a
5 1a 2a 3b
6 1b 2a 3b
7 1a 2b 3b
8 1b 2b 3b

Connection of GCA_PI04 in running RocNet

Depending om cable length, it sometimes happens that RocNet is blocked after plugging in the PI04 in th network.
This can easily solved by soldering a 100 uF (mimimum 16V) close to the connector where PI04 is plugged.
Remind + and - of Elco to be connected at the right place.
Picture will follow shortly.

Prototype 3.
gca-pi04-en.txt · Last modified: 2020/12/30 14:17 by rjversluis