bernhardoj
Posts: 31
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Why my IR LED transmitter not transmit any signal?

Thu Mar 14, 2019 5:17 pm

So, I have been trying to transmit a signal from my IR LED transmitter. I record the signal by using an LED Receiver. But, when I tried to send the signal, the result is nothing. I use my mobile phone camera to see the IR LED light and no light is emitted. I tried to place a normal LED and try to transmit the signal and the normal LED emitted light. So, what is the problem?

NOTE: I could light the normal LED, but not the IR LED.

I follow the wiring up setting from a website like this.
Image
Without the temperature sensor.

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joan
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Location: UK

Re: Why my IR LED transmitter not transmit any signal?

Thu Mar 14, 2019 5:43 pm

How much current are you supplying? I think IR LEDs need a lot more than visible light LEDs

bernhardoj
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Re: Why my IR LED transmitter not transmit any signal?

Thu Mar 14, 2019 6:50 pm

joan wrote:
Thu Mar 14, 2019 5:43 pm
How much current are you supplying? I think IR LEDs need a lot more than visible light LEDs
I use a 5V voltage and a resistor with around 120 ohms.
So, If I'm not wrong, the current calculation would be 5/120 = 0.04 A (CMIIW, I'm still newbie to this thing)

gordon77
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Re: Why my IR LED transmitter not transmit any signal?

Thu Mar 14, 2019 6:59 pm

There's no 120 in the diagram.

Have you tried just putting the 120 and ir diode across 5v?

Brandon92
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Location: Netherlands

Re: Why my IR LED transmitter not transmit any signal?

Thu Mar 14, 2019 7:11 pm

Did you try to power the leds without a serie resistor on 5V. If you did, you probably need to buy two new IR leds.
bernhardoj wrote: I use a 5V voltage and a resistor with around 120 ohms.
So, If I'm not wrong, the current calculation would be 5/120 = 0.04 A (CMIIW, I'm still newbie to this thing)
This is not correct.
To calculate the current through the leds need to use the following formule:
Iled = (Vcc - Vf)/R

Where:
Iled = current through the led
Vcc = voltage of the power rail
Vf = forwards voltage of the led
R = the used resistor

So this give:
Iled = (5-(2*1.5))/120 = 0.0166A = 17mA

Do you have a link / datasheet of that IR led, so we can see if this value is good or not.

drgeoff
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Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 1:13 am

bernhardoj wrote:
Thu Mar 14, 2019 5:17 pm
So, I have been trying to transmit a signal from my IR LED transmitter. I record the signal by using an LED Receiver. But, when I tried to send the signal, the result is nothing. I use my mobile phone camera to see the IR LED light and no light is emitted. I tried to place a normal LED and try to transmit the signal and the normal LED emitted light. So, what is the problem?

NOTE: I could light the normal LED, but not the IR LED.
What software are you using to record and send?

Do you understand that almost all IR remotes use a modulated carrier? viewtopic.php?f=37&t=235655&p=1441145#p1441145

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joan
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Location: UK

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 9:02 am

drgeoff wrote:
Fri Mar 15, 2019 1:13 am
...
Do you understand that almost all IR remotes use a modulated carrier? viewtopic.php?f=37&t=235655&p=1441145#p1441145
The signal will need to be modulated but at this stage it's not even being picked up by a camera. Almost certainly a power issue. I seem to remember having to give my IR LED quite a bit of current (hundreds of milliamps springs to mind).

btidey
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Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 9:32 am

The original circuit is bad There is nothing specifically to limit the current drawn through the two diodes and the transistor.

The voltage drop across an IR LED is about 1.5V so with 2 in series and a 5V supply the current will be determined just by the gain of the transistor and the capacity of the power supply. There is a good chance that the transistor and / or the diodes are fried and need to be replaced.

You need to put a resistor in series with the diodes to determine the current flow when the transistor turns on. IR diodes will give good output with 50 to 100 mA.

So the total voltage drop is 2 x 1.5V (diodes) + 0.2V (saturated transistor + I x R = 5V

R = 1.8V / I

For a current of 50mA you would need a resistor of 36 Ohms. Any value from 22 -> 47 Ohm would work well.
IR.jpg
IR.jpg (36.27 KiB) Viewed 870 times

bernhardoj
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Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 11:02 am

Brandon92 wrote:
Thu Mar 14, 2019 7:11 pm
Did you try to power the leds without a serie resistor on 5V. If you did, you probably need to buy two new IR leds.
bernhardoj wrote: I use a 5V voltage and a resistor with around 120 ohms.
So, If I'm not wrong, the current calculation would be 5/120 = 0.04 A (CMIIW, I'm still newbie to this thing)
This is not correct.
To calculate the current through the leds need to use the following formule:
Iled = (Vcc - Vf)/R

Where:
Iled = current through the led
Vcc = voltage of the power rail
Vf = forwards voltage of the led
R = the used resistor

So this give:
Iled = (5-(2*1.5))/120 = 0.0166A = 17mA

Do you have a link / datasheet of that IR led, so we can see if this value is good or not.
First, thanks for the formula.
Second, here is my IR led data(I bought it by online shopping and copy the specification of the IR led) :
LED 3mm infrared transmitter 940nm
  • Emitting color: Infrared
    Material: GaAs/AlGaAs
    Lens color: Clear / Transparent
    Peak wavelength: 940nm
    Forward Voltage:1.2-1.4 VF
    Emitting distance:15m-18 m
    Power Angle: 25-30 (10-45 available)
    Forward Current: 20 mA

bernhardoj
Posts: 31
Joined: Fri Feb 22, 2019 9:18 am

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 11:06 am

drgeoff wrote:
Fri Mar 15, 2019 1:13 am
bernhardoj wrote:
Thu Mar 14, 2019 5:17 pm
So, I have been trying to transmit a signal from my IR LED transmitter. I record the signal by using an LED Receiver. But, when I tried to send the signal, the result is nothing. I use my mobile phone camera to see the IR LED light and no light is emitted. I tried to place a normal LED and try to transmit the signal and the normal LED emitted light. So, what is the problem?

NOTE: I could light the normal LED, but not the IR LED.
What software are you using to record and send?

Do you understand that almost all IR remotes use a modulated carrier? viewtopic.php?f=37&t=235655&p=1441145#p1441145
I used

Code: Select all

mode2 -m -d /dev/lirc0
to record and

Code: Select all

irsend
to send the signal.
Firstly, I use irrecord but it always stuck at the last dot.

bernhardoj
Posts: 31
Joined: Fri Feb 22, 2019 9:18 am

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 11:13 am

btidey wrote:
Fri Mar 15, 2019 9:32 am
The original circuit is bad There is nothing specifically to limit the current drawn through the two diodes and the transistor.

The voltage drop across an IR LED is about 1.5V so with 2 in series and a 5V supply the current will be determined just by the gain of the transistor and the capacity of the power supply. There is a good chance that the transistor and / or the diodes are fried and need to be replaced.

You need to put a resistor in series with the diodes to determine the current flow when the transistor turns on. IR diodes will give good output with 50 to 100 mA.

So the total voltage drop is 2 x 1.5V (diodes) + 0.2V (saturated transistor + I x R = 5V

R = 1.8V / I

For a current of 50mA you would need a resistor of 36 Ohms. Any value from 22 -> 47 Ohm would work well.
IR.jpg
But, how do you explain that my normal LED is working fine?

bernhardoj
Posts: 31
Joined: Fri Feb 22, 2019 9:18 am

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 11:39 am

This is exactly how I wired it up.

Please tell me if there is anything wrong.

Image

gordon77
Posts: 4004
Joined: Sun Aug 05, 2012 3:12 pm

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 11:41 am

Do you have a photo showing exactly where the diodes etc are plugged in, it's hard to see.

bernhardoj
Posts: 31
Joined: Fri Feb 22, 2019 9:18 am

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 11:48 am

gordon77 wrote:
Fri Mar 15, 2019 11:41 am
Do you have a photo showing exactly where the diodes etc are plugged in, it's hard to see.
I just recently posted it above your reply.
bernhardoj wrote: This is exactly how I wired it up.

Please tell me if there is anything wrong.

Image

gordon77
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Joined: Sun Aug 05, 2012 3:12 pm

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 11:59 am

I saw that but can't see the component legs etc.

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procount
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Location: UK

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 12:16 pm

This won't help your transmission problem, but it's just an observation on your original diagram.

I note the IR Receiver has Vcc connected to +5V and it's output data line directly connected to GPIO23.
What is the specification of that Data output signal? I would have expected to see a voltage divider on the output to bring the voltage down to below 3.3V so you don't fry the GPIO line of the RPi.
PINN - NOOBS with the extras... https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=142574

bernhardoj
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Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 2:05 pm

gordon77 wrote:
Fri Mar 15, 2019 11:59 am
I saw that but can't see the component legs etc.
This is the updated showing legs, hope it clear.
Image

bernhardoj
Posts: 31
Joined: Fri Feb 22, 2019 9:18 am

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 2:12 pm

procount wrote:
Fri Mar 15, 2019 12:16 pm
This won't help your transmission problem, but it's just an observation on your original diagram.

I note the IR Receiver has Vcc connected to +5V and it's output data line directly connected to GPIO23.
What is the specification of that Data output signal? I would have expected to see a voltage divider on the output to bring the voltage down to below 3.3V so you don't fry the GPIO line of the RPi.
I don't know exactly how the specification of the Data output signal looks like. I have put a resistor for the IR receiver output.

gordon77
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Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 2:14 pm

Thanks, much clearer, looks OK to me.

Have you tried with just 5v and a resistor to an ir led yet?

bernhardoj
Posts: 31
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Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 2:16 pm

gordon77 wrote:
Fri Mar 15, 2019 2:14 pm
Thanks, much clearer, looks OK to me.

Have you tried with just 5v and a resistor to an ir led yet?
Do you mean without the transistor?

gordon77
Posts: 4004
Joined: Sun Aug 05, 2012 3:12 pm

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 2:30 pm

Yes, just a resistor and an ir led.

Do you have details of the IR led?

Brandon92
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Location: Netherlands

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 2:35 pm

bernhardoj wrote:
Fri Mar 15, 2019 11:02 am
First, thanks for the formula.
Second, here is my IR led data(I bought it by online shopping and copy the specification of the IR led) :
LED 3mm infrared transmitter 940nm
  • Emitting color: Infrared
    Material: GaAs/AlGaAs
    Lens color: Clear / Transparent
    Peak wavelength: 940nm
    Forward Voltage:1.2-1.4 VF
    Emitting distance:15m-18 m
    Power Angle: 25-30 (10-45 available)
    Forward Current: 20 mA
No problem, so the 120r resistor is fine and you should see it light up.

However:
bernhardoj wrote: This is exactly how I wired it up.

Please tell me if there is anything wrong.
You did connect the IR leds without the necessary resistor. And you need to limit the current trough the leds, otherwise they will be damaged (read dead). Read this tutorial for more information about it.

The next step for you is to trough those two leds in the bin and use two new ones with the correct resistor. See this link for more information how to connect it with a transistor.

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procount
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Location: UK

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 2:37 pm

bernhardoj wrote:
Fri Mar 15, 2019 2:12 pm
I don't know exactly how the specification of the Data output signal looks like. I have put a resistor for the IR receiver output.
Unless you find something to the contrary, you should really add 2 resistors as a voltage divider, otherwise your GPIO pin is at risk of being destroyed as they can only withstand a maximum of 3.3V

Please see this thread for information -> viewtopic.php?f=37&t=233429&p=1429268#p1429268 including a circuit diagram with typical resistor values.
PINN - NOOBS with the extras... https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=142574

bernhardoj
Posts: 31
Joined: Fri Feb 22, 2019 9:18 am

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 2:43 pm

gordon77 wrote:
Fri Mar 15, 2019 2:30 pm
Yes, just a resistor and an ir led.

Do you have details of the IR led?
Do you mean this?
LED 3mm infrared transmitter 940nm
  • Emitting color: Infrared
    Material: GaAs/AlGaAs
    Lens color: Clear / Transparent
    Peak wavelength: 940nm
    Forward Voltage:1.2-1.4 VF
    Emitting distance:15m-18 m
    Power Angle: 25-30 (10-45 available)
    Forward Current: 20 mA

gordon77
Posts: 4004
Joined: Sun Aug 05, 2012 3:12 pm

Re: Why my IR LED transmitter not transmit any signal?

Fri Mar 15, 2019 2:46 pm

Yes, l didn't spot that. As said above try 120ohms. If they don't light up with 5v they are probably dead.

(5v - 1.4v) / 0.02A = 180ohms for one ir led.

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