This page has circuits that use infrared position sensors that are available from may sources on the internet. The circuit board used in the testing and example circuits is shown below.
One use for the Prefab IR Sensors is inputs for robotics controllers. They can also be used in many model railroad applications either between the rails, across the tracks or beside the track.
The IR phototransistor's case is dark so that most of the visible light is blocked but very strong light sources can trigger the circuit.
The example Prefab sensor uses a LM393, dual voltage comparator as the output device. These comparators have a typical output current rating of 16 milliamps. The detection indicator LED draws 3 mA that will be included in the comparator's output current capacity.
The output of the Prefab sensors can be used directly for 5 volt inputs such as microcontrollers and logic devices. A pull-up resistor is not required.
The example sensor does not have hysteresis, therefore, the output will be slow to change states in some circumstances. This could make the sensors unsuitable as a direct input to devices or circuits that cannot tolerate noise or jitter.
If an output with a higher voltage or current capacity is needed, transistors or other devices can be added to the circuit.
The IR LED and the phototransistor can be dismounted from the circuit board and reconnected using wires for easier between the tracks installation and for above or across the tracks.
For above or across the tracks use, the operation of the sensor is reversed and the output will go HIGH when the beam is blocked.
The LED and phototransistor require are not particularly easy to desolder due to the small size of the mounting holes. Take care to not overheat these components.
The LED and phototransistor could also be replaced by matched 3mm LEDs and phototransistors. The phototransitor could be encased in heatshrink tubing to block external light sources if needed.
The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.
If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.
Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.
30 March, 2019