# Frustration over IR transmitter and receiver how do I..?

Discussion in 'Radio and Wireless' started by CABBAGE, Jan 24, 2019.

1. ### CABBAGE

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Nov 17, 2018
I have been trying in vein to assemble a simple breadboard example of an IR transmitter and a receiver (no arduino) just to see it work.

First question: can anyone provide a link to a circuit diagram that works?

Second question: what state does the transmitter (with 555) need to be in?

Astable or monostable and does it produce 38Khz to be received by a tsXX38 reciever? I very new to this and I'm trying to make one work just for proof of concept, then I can adapt from there. Just getting the two to work together has proved to be elusive. All I'm looking for is a transmitter to be received by a receiver and light up an LED (or perhaps output 5V power) if someone can provide some clues or a diagram it would be greatly appeciated,

Last edited by a moderator: Jul 14, 2019
2. ### Harald KappModeratorModerator

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Nov 17, 2011
I don't have one, but there should be plenty to be found by a search engine
It depends on what you want to achieve. If you want to transmit a signal that can be distinguished from ambient light you'd use an AC waveform, therefore the astable mode is in order.
It can, provided you supply the right component values. There are plenty of 555 calculators online.
Type? I can't find a tsXX38 receiver. A basic receiver should receive IR light of any modulation frequency. The limits are stated in the datasheet. Should this be a module, other limits may apply as per datsheet of the module. Do you have a datasheet or a link to one?

You can use a red LED instead of the IR LED to check whether the transmitter operates at all. Or use the camera of your smartphone. Most will show an active IR source as a bright dot.

3. ### BobK

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Jan 5, 2010
TSOP receivers are very finicky about the signal they receive. It must be at the specified frequency ± a few percent. It must also be modulated. If you produce a steady 38KHz, it will initially recognize it, then ignore it. You must produce bursts of a specific range of length followed by gaps of a specific range of lengths. The datasheet will give these figures.

So you cannot just use the raw output of the TSOP as an on off signal. The simplest way to accomplish that is to send repeating bursts with the specified gap. The receiver then sees a signal that is a square wave with a specific duty cycle (ration of on time to period). So the simplest way to implement the receiver would be to trigger a monostable that is slightly longer than the period of the signal (not the carrier). So if you put out a 100uS pulse followed by a 100uS gap, you would set the monostable at say 300uS. Then it would turn on when the first pulse was detected and off 200uS after the last pulse is detected.

Exactly what receiver are you using? Can you link to a datasheet?

Bob

4. ### hevans1944Hop - AC8NS

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Jun 21, 2012
As per usual, it looks like @CABBAGE either gave up, since he didn't get the immediate answer he wanted here, or went on to post his questions in other forums. The Adafruit website has some interesting projects and parts for sale that are used to implement a modulated 38 kHz carrier IR remote control system.

As @BobK noted, the raw unprocessed output of the TSOP IR receiver is not useful for control purposes all by itself. Typically a microprocessor sorts things out, but by transmitting a known, fixed duty-cycle pulse train from, say, a handheld TV IR remote control, this signal could be used with a re-triggerable one-shot multivibrator to detect the occurrence of said pulse train, as @BobK described. An oscilloscope would be useful during the initial setup of such a circuit.

Considering how "simple" it is to interface and program a PIC microcontroller, I would choose the PIC alternative. Your mileage (or kilometers) may differ. Some research and study required.

5. ### TCSC47

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Mar 7, 2016
Not exactly what the OP asked for but if they are simply experimenting an IR or optical audio link can be good fun. I made a system like this many years ago and it worked very well. The only thing I would change in the circuit below is to have the Tx driven by an op amp with the facility to bias on the TX IR LEDs a little bit to move them a bit further into a linearish part of their characteristics. And as Harald says, if you start off with visible LEDs you can see that at least something is coming out of the Tx LEDs.

davenn likes this.
6. ### hevans1944Hop - AC8NS

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Jun 21, 2012
The OP was "experimenting" with a receiver designed to demodulate a 38 kHz PWM pulse train, which is the type of signal typically produced by common hand-held IR remote controls. Why modulate at 38 kHz? Because the ambient environment is full of infrared radiation that would interfere with an un-modulated IR control signal, such as your simple audio transmitter/receiver schematic shows.

Modulation adds information to the infrared signal that allows it to be distinguished and separated from the ambient infrared radiation by the TSOP IR receiver. The pulse-width modulation allows encoding different command functions for the remote control. The raw data output from the receiver (the PWM signal) is normally processed with a microprocessor or microcontroller to determine which command is being sent by the hand-held IR remote transmitter. Unfortunately, the OP refused to consider using a microprocessor or microcontroller to solve their "problem" and abandoned this thread.

Your simple audio IR transmitter/receiver would benefit from a modulation scheme, too. I have a pair of stereo IR headphones that allow me to listen to television without disturbing my wife (and others) by turning the TV volume too high. I haven't investigated how they do it, but the two stereo channels are somehow transmitted and then separated. There is just one "transmitter" with dimly visible red/ir LEDs and two "receivers," one for each ear. Audio quality is just so-so, but adequate for most TV viewing. There is some sort of "quieting" circuit because if I leave the room while wearing the IR headset the sound vanishes. I have a corded headset for "high fidelity" listening, although my hearing is no longer in the category of high fidelity without a lot of boost for both low frequencies and high frequencies.

Anyhoo, this thread is dead, but if you want to start another one based on audio transmission via an IR LED, that would be interesting. It might even be possible to re-purpose a TSOP receiver module to accept audio modulation, instead of digital signals, and somehow recover the audio. Bear in mind that the maximum carrier frequency is limited by the frequency response of your IR detector. A high-speed infrared PIN detector is already integrated into the TSOP receiver module, but you might want to explore using your own separate IR sensor driving whatever electronics is appropriate for your modulation scheme. This sort of thing lends itself well to laser communications too of course... it just takes somewhat more skill.