ir LEDs not working - not enough power?

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To overcome this problem i decided to buy some new LEDs with more power (100mA instead of 20mA). After i had hooked everything up with the new LEDs, nothing was working anymore.
May i have to little amperage from the Arduino to the LED?

Yes the Arduino should only be asked to power something that draws below 20mA.
What we need here is a schematic of the hardware you have both the LED driver and current limiter. You might also try an IR filter over the receiving sensor to block out ambient light.

Grumpy_Mike:
What we need here is a schematic of the hardware ...

A pretty Fritzing drawing is not a schematic.

Run the simple blink sketch.

What is the voltage across the 22R when the transistor is ON ?


You could try 2+ LEDs each with its own 22R.

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renzosmania:
First of all, the output-Voltage of the Arduino is 4.6 V (measured Vcc and ground of the arduino).

With the new LED still in place the voltage across the 22R is 0.
Therefore, 22R is too high, right?

I took some measurements with the old LEDs (across the same 22R) --> the voltage now shows 2.7 Volts.

If I connect the 22R directly to ground the Voltage reaches 4.1 Volts.

The voltage drop of 0 could indicate that the polarity of the new led is reversed.
A 22R resistor between 5V and GND will begin to get warm.

With the new LED still in place the voltage across the 22R is 0.
Therefore, 22R is too high, right?

No not at all.
A voltage drop of zero means there is no current at all flowing through the resistor, therefore the led can not shine at all.
So there is something wrong with the LED or the transistor. If you are just replacing the LED and keeping everything else the same then the LED could be the wrong way round or the new one could have thinner wires and is not making contact in the bread board.

I haven't looked at your code, but if it worked in dim light with the old LED, it's probably ok. But as others have mentioned, my bet is that the LED is backwards or not making contact. But remember that you can see whether the LED is turning on by looking at it with your phone's camera.

If you are powering the Nano through the USB port, then you aren't depending on the Nano's 5V regulator for any of this. However, the USB 5V supply does go through a Schottky diode, and you may be pushing the limit of how much current that diode can handle. If that's a problem, the voltage on the Nano's 5V pin would sag significantly when the LED is turned on. I think this is probably not the problem here, but you're drawing roughly 130mA through the LED, and everything else you're using should be able to handle that on a non-continuous basis.

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You must learn to trouble shoot your circuits.


To get the current flow in a cct., measure the voltage across the series resistor, take this voltage value and ÷ by the resistance.

0v ÷ 22 Ω = 0 ma ??? OMG something must be wrong, there is no current flow.

Learn from this example !


Note the flat side on the LED is the cathode :wink:

renzosmania:
Oh my god. I'm so embarrassed . . .
:slight_smile:

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Of course none of us has ever made such a mistake. No, not once.

renzosmania:
Oh my god. I'm so embarrassed :sweat_smile:
Of course you were right. I put the ir-LED in the wrong way round. These were the first LEDs i used that have longer cathode pins than the anode pins

Common misunderstanding - pin length is not the polarity indicator. For standard LED housings
the cathode side has the flat section.

The pins being of different length is a convenience for board-stuffing, and varies from manufacturer to
manufacturer.

The 1k base resistor is rather high, try 220ohms for a cooler transistor...

I remember the first LEDs I bought back in the 1970's. They got a flat side. But all of the LEDs I have bought recently only have a longer anode pin - no flat side.

thehardwareman:
I remember the first LEDs I bought back in the 1970's. They got a flat side. But all of the LEDs I have bought recently only have a longer anode pin - no flat side.

Then you are not looking closely enough at the small ring on the end that the wires emerge from, they all have a flat on that ring.

Grumpy_Mike:
Then you are not looking closely enough at the small ring on the end that the wires emerge from, they all have a flat on that ring.

Are you thinking 5mm or 3mm because I am looking at a 3mm LED here with no flat marking on the coloured body.

6v6gt:
Are you thinking 5mm or 3mm because I am looking at a 3mm LED here with no flat marking on the coloured body.

Don't have the LEDs in front of me right now. I got both 3, 5, and 10 mm and can't remember seeing any flat side on them.