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IR Receiver - gives out data only while disconnecting/connecting it to ground

martinselva

I am following a guide to setup my IR ( rev + transmitter ) program on my RPI 3

 

IR receiver : TSOP1738 38Khz Infrared Receiver 8051

image

 

Problem: After configuring the GPIO perfectly, I am not able to get any output while using below command

 

sudo mode2 -d /dev/lirc0

 

But when I try unplugging the ground and plugging it again - I get random output like this.

image

 

Is it because the IR receiver is not getting enough power? Do I need to add something else to power it rightly..Please help!

 

 

  • 0

    The data sheet for the TSOP1738 says that its working supply voltage range is 4.5- 5.5V - there is no reason it should be expected to work from  a 3.3V supply.

    A quick Googling shows that other people have used this part on 3.3V but they don't make it clear how many (if any) they tested.

     

    The other things to look out for is that there should be  a decoupling capacitor and that you need to use  the correct frequency of TSOP17XX to match the transmitter.

     

    If you can get hold of a TSOP382XX or TSOP384XX, very similar but designed to work with 2.5 - 5.5V supplies and likely to work with the pi. (Google 'Vishay TSOP382' for data sheet)

     

    Unfortunately you need to be very careful with "guides" from the internet - it is a good idea to check all the component data sheets before building anything.

     

    MK

  • 0 in reply to michaelkellett

    Thanks MK for your reply. Couple of questions

     

    MK >> TSOP1738 says that its working supply voltage range is 4.5- 5.5V

     

    I tried it with 5v - no luck

     

    MK >>If you can get hold of a TSOP382XX or TSOP384XX, very similar but designed to work with 2.5 - 5.5V

     

    Sure, will search for it on Amazon!

     

    MK >> there should be  a decoupling capacitor and that you need to use  the correct frequency of TSOP17XX

     

    Sounds good. Let me first see if I have one and 2ndly figure out where to place it rightly.

     

    Thanks once again MK

     

     

  • 0 in reply to michaelkellett

    It's working for me now!

     

    Thanks for your suggestion - I referred the data sheet and found that I made huge mistake with the Pin - placed it at the wrong place ( ya- blindly followed the guide.. my bad )

     

    Fixed it and it's working as expected!

  • 0 in reply to martinselva

    I don't understand your drawing of the connections. The TSOP1738 datasheet shows the left pin (bump facing you, pins down) as GND, middle as power and right as the signal output. Your drawing implies you've connected them differently (assuming your red wire is the postive supply, the black is GND and the white is the signal out).

     

    I see you've discovered that for yourself. Bonus point for reading the datasheet at all, but you should do it before not after.

     

    A decoupling capacitor goes across the supply connections (one side to positive, the other to ground) close to the device. 47nF or 100nF is a fairly usual sort of value if the datasheet doesn't tell you any different. In this case, the datasheet gives a more elaborate filter - see the application circuit which shows a filter made up of a 330ohm resistor and a 4.7uF capacitor. That implies that the device doesn't reject low-frequency power supply noise very well at all. It's better to have the decoupling, but it's not make or break for it working.

  • 0 in reply to jc2048

    Jon, there are two kinds of "decoupling".

    The one that's essential for digital chips is that a digital chip that you might know uses "about 1mA" might use the occasional 1A for a nanosecond say 1000 times a second. That's why you have a decoupling capacitor near the chip. It can provide those really short bursts of extremely high current.

     

    On the other hand, there are chips that perform analog functions. Those chips need an "analog powersupply" that has as little noise and ripple as possible. There, you might chose to use a resistor and a capacitor to create a separate "analog" powersupply in the circuit.

     

    I don't think that this has to do with "reject low-frequency power supply noise". .... And yeah, even without that it will usually work.

     

    There are lots of "howtos" that provide easy-to-use diagrams where the physical connections are depicted. Many people don't have the skills to read a real schematic and prefer that. Those would NEVER consult a datasheet before trying to build something. So I think it is a very good thing that Moz is different and HAS looked at the datasheet!

  • 0 in reply to rew

    If you feel I've insulted Moz, then I apologise unreservedly to him. That wasn't my intention.

     

    I thought I was congratulating him for consulting the datasheet and coming up with his own answer even before anyone could reply and help, though I can see that the tone of my post wasn't right and liable to be misunderstood. Even on a good day, I'm not the world's best writer.

     

    Are you sure that a decoupling capacitor can supply 1A in a nanosecond?