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GCA-PI07 Transformer Sensor


Discontinued, due to unavailability of chip PCF8591 in DIL16. Alternative GCA94.


Sensoring trains is a very essential part of automatic train control.
Rocrail is no exception for that.
There are various ways of keeping track of your trains.
For a longer time GCA93 current detector has been widely used because its excellent reliability.
This GCA93 is also, connected to a GCA_PI02 very useful for RocNet network.
But there is one very little disadvantage, using current detectors like GCA93 :
It looses 1.2 V of your booster power.
In practice it is hardly noticeable, specially with the modern decoders with load control.
The GCA_PI07 is made in a different way, which avoids this 1.2 V lost.
There is hardly any loss at all (approx 5 mV)
The disadvantage is a larger board, compared to GCA93.
Max four of these boards are to be connected to one Raspberry Pi.
A dip-switch on board selects the address, see table below.
The sensibility of two groups of 4 inputs can be influenced by jumpers.


  • 8 current inputs on each board
  • Direct link to I2C in RocNet.
  • Very low power loss due to use of transformers.
  • Total 32 sensors inputs to one Raspberry Pi.
  • The load per sensor is reported to Rocrail for Background Color.

The Hardware

Final product Professional board
gca_pi07_pict03.jpg gca_pi07_pcbpict.jpg

Dip Switch settings

Maximum of 4 boards can be used to one Raspberry Pi.

sensors SW 1 SW2
1..8 OFF OFF
9..16 OFF ON
17..24 ON OFF
25..32 ON ON

Jumper settings

Jp1 and Jp2 are to seelct a more or less sensitivity to the inputs.
There indications on board : 5 and 3.
Normal settings will be a jumper to pos 5.
If you need a lightly better sensitivity put the jumper on pos 3.
Jp1 is for input 1..4.
Jp2 is for input 5..8.


N.B. Only complete ordered kits will be supported!

Two ways of connecting railsections

To connect railsections to GCA_PI07 there are two options.
First, the easiest way is NOT to use J2 connector, but instead loop the wire that feeds the rail section through the coil.
Usually just feeding through is sufficient, but with lower currents like waggons with 10K resistor between
the wheels, an extra winding will be needed.
It is never critical to use more windings.
The second option is to use connector J2.
But then you need to make 2 windings of isolated wire on each coil and connect the ends to the free solder pads
on both sides of each coil.


GCA_PI07 is using a transformer to detect current.
But like every transformer, the inputs of this unit will only detect ac current.
This current can be any digital signal from central units, but also the 50 Hz of a Märklin system.
It will definitely not work with dc powered analog trains.

gca-pi07-en.txt · Last modified: 2020/01/13 12:41 by smitt48