Remote light detector (discrete components)

Discussion in 'Wireless & RF Design' started by Synaps3, Mar 23, 2019.

  1. Synaps3

    Thread Starter Active Member

    Jun 5, 2013
    99
    3
    Hi,
    I have a pretty simple project I want to do, but I am unable to find any examples aside from arduino and I want this to be small, compact and simple.

    What I want to make is a sensor that uses a photo diode, maybe transistor, and a crystal oscillator. I am not sure on the exact details of how to make this though. I basically just need a device that will output an RF carrier when light is detected. On the other end I will need a device that just detects the RF carrier and lights an LED to indicate that there is light in the remote location.

    Could anyone help me out with this? I would greatly appreciate a schematic. If anyone is very helpful, I will also donate to your paypal if you like.

    I may also be interested in a pre-made device if one exists, but I am unable to find one.
     
  2. jpanhalt

    Expert

    Jan 18, 2008
    7,154
    1,574
    Please tell what you are trying to do, not how you want to do it.

    Why do you need an "RF carrier" when light is detected. Like, how intense does the light have to be to register? Wavelength...have you considered that infrared is light? An RF carrier per se is a lousy way to communicate to a remote location. There will be false triggers. What would be the consequence of that? How far is the remote location?
     
  3. Synaps3

    Thread Starter Active Member

    Jun 5, 2013
    99
    3
    I am trying to make a remotely monitored light detector. The range is about 150 ft max.
    Making the transmitter is easy and I already figured it out, but how do I make an RF carrier detector? I searched CW detector and I'm unable to find anything that's not a full featured radio receiver. Could someone please help me to make this?

    Thanks.

    I understand about the false triggers. I can mess around with the sensitivity. It's OK if I get some blips sometimes. I just need the general idea that a light is on in the remote location.

    I know about RF modules and arduino, but I want to do this with simple components and preferably no MCU.
     
  4. pmd34

    Active Member

    Feb 22, 2014
    353
    149
  5. Externet

    AAC Fanatic!

    Nov 29, 2005
    1,335
    169
    Synaps3 : Am after the same aim of RF carrier detection for another application; and so far have not seen other methods than a receiver. Cannot see the 433MHz RX modules providing indication of carrier presence. Bought them and could not figure how to do it yet.
    Am waiting for a chip AD8307 to attempt something.
    Do you need a permanent indication of 'light presence' or just a pulse when light turns on ?
    The transmitter could be a crystal oscillator powered by the remote light and a proper antenna at its output pin should reach 150 ft. Did it once years ago and worked :eek:

    [​IMG]

    Another odd way is the remote light powering a 1mW laser pointer module from the 99 cent store, will project a red dot where you want telling there is light presence.
     
  6. sghioto

    Well-Known Member

    Dec 31, 2017
    1,039
    157
    Noise operated squelch is one method.
    SG
     
  7. Janis59

    Active Member

    Aug 21, 2017
    699
    107
    If I correctly realized the aim, I`ll tell with my wording, You need to detect in larger distance do the light source (lamp, LED etc) is switched on or off and have relatively immune against the external lights (sunlight).
    If so, the one excellent tablet is 567 (www.ti.com/lit/ds/symlink/lm567c.pdf) with better description in the http://www.amalgamate2000.com/radio-hobbies/radio/ne567_tone_decoder_as_am_fm___de.htm
    Thus, feet-3 must serve as sync pulse output, what somehow (wire, RF channel, optically etc ) is transferred to the "lamp". And lamp is fast enough to work with a phase and timing of this sync. Means You have only choice of LED or laser diodes. In the near end in front stays light-sensitive diode or FEM :)) or at least photoresistor, then transimpedance cascade, slightly resonant amplifier adjusted for proposed sync frequency, what ends into input of IC-567. When it realizes the right freq and right phase, it generates 1) AM detected signal and 2) FM detected signal and 3) signal yes/no about right signal existance. System is highly stable against Sunlight and practically insensitive to trials to fox it by separate unsync oscillator making the right freq but wrong phase. Intruders must stay afraid!

    Note: LM567 datasheet link not working so replaced by moderator.
     
    Last edited by a moderator: Apr 9, 2019
  8. DickCappels

    Moderator

    Aug 21, 2008
    5,456
    1,698
  9. Externet

    AAC Fanatic!

    Nov 29, 2005
    1,335
    169
    Hello Dick.
    Will the data pin at Tx held 'hi' permanently correspond to a data pin 'hi' at RX when units are powered up ?
    I believe this could be the schematics as seen on the web...
    [​IMG]
     
    Last edited: Apr 9, 2019
  10. DickCappels

    Moderator

    Aug 21, 2008
    5,456
    1,698
    Yes they work that way but I think you need to you modulate the transmitter with pulses so the receiver will see the envelope. .

    Those are the classic circuits, though sometimes the regenerative detector is preceded by a dual gate MOSFET buffer to reduce the detector's oscillation frequency getting into the antenna.
     
Loading...