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GCA173 infrared opto-gate for counting passing wheels.


By Peter Giling


The board GCA173, with diiferent firmware, can be used as rather simple real wheelcounter.
This wheel counter option is already available in the sensor properties in Rocrail
but besides the not very popular GCA141, it is hardly used.
But I must confess, thet it worked perfect on my HO demo unit.!
The use of a very small opto-gate of Sharp, type GP1S097HCZF makes this a nice feature.
The slot opening is just enough to match the size of the HO wheel flanges.
Because the input from the opto-gate is reversed in comparison with a hall sensor, the firmware on GCA173 processor
is slightly different from GCA173 with hall sensors.
Also, because all leds show when no sensor is inactive, quite some extra current is needed, whitch I do not like.
But with the modern high effinciency leds that is no problem.
Therefore RP1 to RP4 will be changed to 3.3 Kohm.

The opto-gates are connected to the hall sensor connectors.
This creates the need of one extra 470 Ohm resistor, mounted at bottom of opto gate between points 1 & 2.
The two pictures above show that the resistor is best situated at the opposite side as the sensor.
The sensor itself is shown in sutch a way, that it is easy for you to determine the right position, showing the angled sides.
The three connection points are to solder wires to connect them to the Hall sensor connectors of GCA173.

Connections to GCA173 remark
These connections match the way hall sensors are connected
1 +5 Volt = square pad
2 0V
3 S signal

Since most LocoNet, CAN, RocNet and WIO- units have some restrictions regarding the minimum length of a pulse,
this wheel counter is not suitable for high speeds, when connected directly.
To make it compatable all over, the minimum pulse length, send out from GCA173, is set to 80 msec.
This restriction mainly also has to do with the distance between two following wheels.
Different systems will be tested about the limit of speeds.
But there is one other future option in the firmware.
It will enable to have the GCA173 count all incoming pulses(wheels) end send out that info
as a 80 mSec pulse train.
This assures that no wheel is missed even in higher speeds and/or shorter distance between the wheels.
More info about that limit will follow after some serious tests, to be performed first, before publishing.


Bill of materials:
GCA_OK4 pcboard
resistor 470 Ohm 1/8 Watt
opto-gate Sharp GP1S097HCZF


The firmware adapted to opto gate real wheel counter firmware will follow shortly
gca173_opto_slot_en.txt · Last modified: 2023/08/12 13:05 by phg