Can someone please answer a few IR sensor questions?(warning: very wordy)

Thread Starter

FuneralHomeJanitor

Joined Oct 12, 2019
34
I recently purchased a cheapo set of IR receivers and transmitting diodes. Before using the transmitter diode I want to become more comfortable with the receiving part so I have been messing around with my tv remote using an oscilloscope on my computer to see if I can register an output voltage, and will be attempting to amplify it next. I have had mixed results and can’t find much information on this part in this package and the datasheet is entirely in what appears to be chinese or another asian language.

After learning what I can find about this particular package style if I understand correctly I have learned:

One pin is VCC, another is GND, and a third pin is an output pin.

I pressed buttons on my remote and have registered different voltages, one was actually as high in the 3 Vpp range and others are typically around 50 or 500 mV(I can’t remember and the results don’t seem reliable) but there is undoubtedly a spike at times. I don’t know why the IR sensor seems to stop working shortly after but maybe I am destroying it accidentally since I can’t read the data sheet.

I am using a 5 V supply and all I did was wire a 10k potentiometer with the CW pin tied to the IR output pin and the wiper to ground to use as a variable resistor.

My eventual goal is to make a latching circuit that lights an LED by pushing the remote button.

I am sorry for the wordiness of this post but I can’t seem to find much info on this package and don’t really understand why it would stop working because I am not drawing much current, and I have seen some indication it does work. It is incredibly frustrating and without explaining the exact situation I don’t know if I will be able to figure out what’s going on. Any help would be great, thanks in advance.
 

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AlbertHall

Joined Jun 4, 2014
11,309
That IR sensor expects a modulated IR beam. It has circuits to explicitly block continuous IR to avoid the effects of ambient light.
It should give signals for a remote control but won't work well with continuous illumination.
 

Thread Starter

FuneralHomeJanitor

Joined Oct 12, 2019
34
So it wouldn’t be possible to use that 38 khz signal to trigger a latching circuit that has a separate circuit with an LED? I was just wanting to use it for that initial signal to trigger a separate circuit and I feel like this is something that is definitely possible and shouldn’t be overly difficult either
 

Thread Starter

FuneralHomeJanitor

Joined Oct 12, 2019
34
Here's a datasheet for something similar in English: https://www.pololu.com/file/0J892/tsop384.pdf

Vishay is a large producer of them, but its site was down when I checked. The datasheet includes a description of how they work. They will not work with a steady IR beam. The beam needs modulation, often in the range of 38 kHz to 100 kHz.
I know this particular sensor uses 38 khz and my tv remote can produce a modulated signal. At one point I could actually see the modulated code appear as a waveform of high and low voltages on the scope, but then it stops working. I am not sure if I am destroying the device but most likely am because I have tried 3 of them and had the same experience with all 3. I don’t understand where I am going wrong if this is the case because I am not really using too much current
 

LesJones

Joined Jan 8, 2017
3,172
You would be better of starting yith some KNOWN parts for which you can download data sheets. It sounds like you don't even know if this is just an IR phototransistor or if it contains filtering and detection circuitry. Most IR receiver devices used in TVs etc have a 38 Khz filter (But some use other modulation frequencies. I think 57 Khz is another frequency that is used.) They also need to see a pulse stream. They will not work with a steady 38 Khz modulated signal. If it is just a simple detector you should see bursts of 38 Khz (Or some other frequency.) when you look at it's output on you oscilloscope. If it does contain signal processing then you will see strings of pulses with the code for each key on the remote control.

Les.
 

jpanhalt

Joined Jan 18, 2008
11,088
I know this particular sensor uses 38 khz and my tv remote can produce a modulated signal. At one point I could actually see the modulated code appear as a waveform of high and low voltages on the scope, but then it stops working. I am not sure if I am destroying the device but most likely am because I have tried 3 of them and had the same experience with all 3. I don’t understand where I am going wrong if this is the case because I am not really using too much current
I am not surprised. The remote has a particular coding algorithm. It does not transmit a continuous code. For example, it way send the code once, then send the code in reverse (as error checking), then stop sending. There are a variety of schemes, but they all include a modulated signal that is received and translated to a digital "output" signal. Here's what I am describing (page 2 of DS):

1607885074801.png

The output will be a digital code; you should not see the 38 kHz modulation. Does you scope allow you to capture a single trigger. That is, set the trigger to detect a down going edge (or up). It should pulse show the pulse. You will need to adjust the sweep appropriately. You shouldn't need any amplifier if the receiver is like the ones I am discussing.
 

Thread Starter

FuneralHomeJanitor

Joined Oct 12, 2019
34
I am not surprised. The remote has a particular coding algorithm. It does not transmit a continuous code. For example, it way send the code once, then send the code in reverse (as error checking), then stop sending. There are a variety of schemes, but they all include a modulated signal that is received and translated to a digital "output" signal. Here's what I am describing (page 2 of DS):

View attachment 224788

The output will be a digital code; you should not see the 38 kHz modulation. Does you scope allow you to capture a single trigger. That is, set the trigger to detect a down going edge (or up). It should pulse show the pulse. You will need to adjust the sweep appropriately. You shouldn't need any amplifier if the receiver is like the ones I am discussing.
I have seen the pulses but I was able to use the similar datasheet posted in this thread to realize this device needs a resistor for the Vcc pin and believe I was shorting the Vcc pin and destroying the component. Right now it seems to be working with the vcc pin in series with a 2.2k resistor connected to the supply
 

Thread Starter

FuneralHomeJanitor

Joined Oct 12, 2019
34
You would be better of starting yith some KNOWN parts for which you can download data sheets. It sounds like you don't even know if this is just an IR phototransistor or if it contains filtering and detection circuitry. Most IR receiver devices used in TVs etc have a 38 Khz filter (But some use other modulation frequencies. I think 57 Khz is another frequency that is used.) They also need to see a pulse stream. They will not work with a steady 38 Khz modulated signal. If it is just a simple detector you should see bursts of 38 Khz (Or some other frequency.) when you look at it's output on you oscilloscope. If it does contain signal processing then you will see strings of pulses with the code for each key on the remote control.

Les.
It is 38 khz and filters the signal, I bought it for a couple bucks thinking I could learn after it gets here and play around but everytime i look up the sensor I see the little arduino sensor that looks like a PCB(which may work the same way) or the black ir diode with out the metal casing around it, I see the strings of pulses because I am using my tv remote which has the coded pulses just to see if it picks up a signal on my scope, I think I was shorting the VCC pin and destroying it, I put a 2.2k resistor in between and I am happy so far with my results
 

AlbertHall

Joined Jun 4, 2014
11,309
If you try different sensors, you need to get the datasheet for the particular sensor that you have as they don't all have the same pinout.
 

Sensacell

Joined Jun 19, 2012
2,821
The other problem is that these receiver modules have an AGC (Automatic Gain Control) that fights you in this application, this makes the detection threshold very fiddly.
You might get this to work, but it's not really the best approach.

This video goes into detail on how these work.

 

BobTPH

Joined Jun 5, 2013
3,308
You would not destroy the device by connecting directly to Vcc. The resistor and capacitor in the application circuit are to filter out noise.

Bob
 
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