Infrared - Proximity Detector

  The circuits on this page are for an Infrared - Proximity Detector using the Vishay Electronics - TSOP4830 "IR Receiver Modules for Remote Control Systems".

  The detectors are designed for short range - reflected light operation but can also be used for short range, 'broken beam' detection as well.

  This circuit was designed primarily for Between The Rails detection of model trains.

  In this circuit the TSOP4830 Infrared receiver is used as a sensitive detector that does not require shielding from room lighting. The detector will work under almost any lighting condition from complete darkness to full sunlight.

  As a guide, if a TV remote control will work in a particular area then so should this circuit as the TSOP4830 would normally used in conjunction with a remote control for a television or VCR.

  This circuit will work in almost all light conditions but it can be affected by infrared remote controls. For its designed use this sould not be a problem.

  This circuit is more complex than typical infrared or visible light sensitive detectors at this site and elsewhere but will work in a wide range of light conditions.

Basic Infrared - Proximity Detector Circuit

  The following schematic is for a basic version of the Infrared - Proximity Detector used on this page.

Datasheet (PDF) for the TSOP4830 at www.vishay.com

  In the basic proximity detector circuit, the hand-held remote is replaced by an infrared LED driver that uses a 556 dual timer. The two oscillators in the 556 simulate the pulsed carrier signal of the remote but without the information such as volume or channel that would normally be sent to an appliance.

Basic Circuit Operation

  The upper portion of the circuit uses two astable 556 oscillators, IC 1A and IC 1B to drive an infrared LED. IC 1A operates at approximately 3Hz with a duty cycle of about 9 percent. IC 1B is adjusted to 30 kHz (the design operating frequency of the TSOP4830) with a duty cycle of about 52 percent.

  The 556 - LED driver circuit produces an approximately 10 millisecond burst of 30 kHz light 3 times per second via the infrared LED.

  The lower portion of the circuit is the IR detector, time delay and output section. The output of the voltage comparator, IC 3, produces a steady LOW - open collector output when infrared light of the correct frequency is detected by the TSP4830 receiver IC.

  1.   When the IR Receiver Module receives a sufficiently strong 30 kHz infrared pulse from D1, its output, pin 3, will go LOW for the duration of the pulse. (About 9 milliseconds.)

  2.   When the output of the IR detector goes LOW, the voltage at the PLUS input of comparator, IC 3, will be made LOW and the comparator's output will go LOW. As long as the infrared pulses are seen by the receiver module the output of the comparator will remain LOW.

      The 4.7uF capacitor provides a time delayed resetting so that the output of the comparator is steady between the IR pulses.

  3.   When the 30kHz infrared signal is no longer detected, the 4.7uF capacitor will charge and the output of the comparator will go HIGH.

  In typical circuits the output of the comparator would control a LED or drive a relay.

Typical Installation Of The Proximity Detector

  The next diagram illustrates a typical model railroad installation method for the emitter and receiver for the proximity detector.

  The infrared emitting LED is mounted through a 3/16" hole drilled through the roadbed.

  The LED is encased in a section of heatshrink tubing to prevent the light from reaching the receiver directly from the sides of the LED.

  The top of the tubing is flush with or slightly higher than the top of the ties. The bottom of the tubing should extend about 1" below the bottom of the infrared receiver IC.

  The IR receiver module is mounted through a 1/4" hole drilled through the roadbed.

  The top of the receiver module is at the bottom of the ties with the lens of the receiver facing the IR LED.

Across The Track Installation

  The TSOP4830 Receivers are very sensitive and will need to be shielded from all sources of IR signal except the LED that is directly across from the receiver when used in a 'Break the Beam' situation.

  Mounting of the emitter and receiver depends on the particular situation but many options are possible.


Proximity Detector Notes

Using The Infrared - Proximity Detectors

Is The IR LED Working?

  Infrared light is not visible to the naked eye, however, a digital camera can be used to view the IR light if it does not have an IR blocking filter on the lens.

  The image may not be very bright but close-up or in a darkened area the light should be visible on the camera's display screen.

Proximity Detector - 30KHz Carrier Frequency Adjustment Notes

  The TSOP4830 infrared receiver requires a 30KHz carrier frequency from oscillator IC 1B. There are two methods that can be used with the detector circuitboards to set this frequency.

  METHOD - A uses five fixed resistors to set the 30KHz frequency of IC 1B.

  METHOD - B uses a potentiometer. This is easier to calibrate but can be easily be put out of calibration.

Other Information

TSOP4830 Case Dimensions

  Other references: -

  Ir Receiver Modules.

  Voltage Comparators.

  555 and 556 Timer.

  Current Limiting Resistor Calculator information.

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Please Read Before Using These Circuit Ideas

  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 detectors.

  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.

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05 February, 2014