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S88 Occupancy Detectors

S88 Occupancy Detector
There are different types of detectors that you can connect to the S88 inputs, the simpliest is a reed with a magnet under the locomotive, another one is to use a opto-coupler , other options include the use of transistors and infrared.

Example of occupancy detection:


1- Reed is placed under the track and when passes the locomotive or a wagon with a magnet in its inferior part, the reed closes and connects input 3 to ground.

2- When a locomotive is in the isolated section of the bridge of diodes, the current flows from booster, through the motor, crosses two diodes in series of the bridge of diodes (B1) and returns to booster. In the diodes there is a voltage drop of 1,4V enough to feed the LED on the opto-coupler through a resistor (R1) the transistor on the opto-coupler connects input 4 to ground.

3- In the other isolated section, when there is a locomotive, the current flows to one of the diodes (D1 or D2), the voltage drop of 0,7V feeds the transistor (T1) through the resistor (R2) and connects input 8 to ground. (through the ground of booster that this connected to the command station)

Example of a Circuit board with 4 detectors for 4 sections:

The two first isolate totally the feeding of tracks of S88 power, third no, of the last one Gonzalo has sent me a photo of how he has done, here you see four detectors, for four isolated sections of via:

Example with Infrared:

Detection can be done using a infrared barrier, in this case when interrupting the train the beam of infrared light between the emitter and the receiver it connects to ground the input of the S88.

It is necessary to arrange the emitter and the receiver faced and in diagonal to the track so that the space between wagons does not affect the detection.

More information on:   Basic Visible and Infrared Light Detectors

More information on:   Circuits for Above and Across the Track


In internet you find several circuits of infrared barriers, Carlos Viva has sent me the photos of how he has constructed following the scheme of R.Paisley for four detection zones.