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Topic: IR Led (Read 3871 times) previous topic - next topic

Grumpy_Mike

So you are saying if you have a crap constant current circuit you will get crap results. Doh!
That is no reasion to abandon the concept.

mjkzz


So you are saying if you have a crap constant current circuit you will get crap results. Doh!
That is no reasion to abandon the concept.


What I am saying is that the ripple and ability to handle pulsing requirements on a constant current driver is too high, even a decent CC driver might not be suitable when a high quality, high gain IR receiver module is used.

Most CC driver/circuits are designed for continuous supply to load and it has little concern about ripple because human eyes could not tell (but high quality IR receiver module does)

A simple MOSFET and resistor provides much better solution than using CC driver in this application.

So it has nothing to do with crap components, it has everything to do with suitability/selection of components/circuit in my application.
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dc42


A simple MOSFET and resistor provides much better solution than using CC driver in this application.


No, a mosfet, transistor and a couple of resistors configured as a linear constant current regulator provides a better solution (although if you are running the IR LED from a regulated supply, then a mosfet and series resistor is adequate). But you are correct in that the usual switching regulators are not designed to be modulated at 38kHz.
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mjkzz



A simple MOSFET and resistor provides much better solution than using CC driver in this application.


No, a mosfet, transistor and a couple of resistors configured as a linear constant current regulator provides a better solution (although if you are running the IR LED from a regulated supply, then a mosfet and series resistor is adequate). But you are correct in that the usual switching regulators are not designed to be modulated at 38kHz.


Yes, agree with linear cc approach and I was thinking of using LM317, but in the end took the simplest approach -- MOSFET + current limit resistor.
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ceci0


I was able to set up the circuit with a 2N3904 transistor. I'm using external power. The circuit works, I can see the LED flashing with a digital camera, but the flash is very weak, less than using it directly on Arduino PIN.

I'm guessing: the library I'm using (legopowerfunctions) uses a very fast pulsing to send commands. Something in the circuit must be revised for this reason?

Thanks,


Runaway Pancake


I was able to set up the circuit with a 2N3904 transistor. I'm using external power. The circuit works, I can see the LED flashing with a digital camera, but the flash is very weak, less than using it directly on Arduino PIN.


How certain are you that it's all wired right?
How about using that digital camera of yours to take a good quality picture of your set up, one where all of your wiring can be seen and analysed, and sharing that with us?
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Don't react - Read.
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ceci0


...pretty sure....but not 100% sure....so here is the picture (attach)


ceci0

sorry...forgot some details:

orange is VIN pin
yellow is ground
green is the PIN 13 of arduino to control flashes

Runaway Pancake

That looks right, needed to be sure.
This time you're observing the IRED result with "legopowerfunctions".
Was that the case before?
Is there no improvement in performance with this?
How does it seem if you just use the Arduino to turn it on versus the other?
Not to say that the camera CCD is the perfect infrared receptor, but I would expect a difference side-by-side.

> > > Is that a 470? base resistor?  If so, put another in parallel with it, to increase the base current.
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

ceci0


Thanks for your time..
I always used the same program. So, to recap:

- I uploaded a program on Arduino
- with IR LED directly connected to PIN 13 (with a resistor) I was able to see flashes (with camera) and I had a 30cm range
- with the new circuit (and same program), I flashes are very very weak, I can hardly see them

The resistor is a 4.2K ohm. I also tried with a lower one but I had the same behavior.

Runaway Pancake

#25
Mar 30, 2013, 05:34 pm Last Edit: Mar 30, 2013, 05:40 pm by Runaway Pancake Reason: 1
I just wired up two IREDs, side by side, one with 70mA and the other with 8 mA.
I will upload a picture of that.

4.2k is not allowing enough base current, the transistor is starved.
Is that a brand-new transistor?

How does it look if you upload the "Blink" sketch?

> > >
70 mA on left, 8 mA on right



Change base resistor to 1K.
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

Runaway Pancake

That resistor looks like yellow-red-brown?  That would be 420?
What is the value of the IRED's resistor?  brown-red-brown, 120??
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

ceci0


OK, the 1K resistor solved the issue!

Now I have at least a couple of meters of range (may be more, I didn't tested).

Thanks soooo much for your help!


Runaway Pancake

OK - Good!
I got out my Arduino, too, and wired this up, with an IRED no less.
Just as a Sanity Check!
I'm using the 5V (USB) and my IRED resistor is 51?, that comes out to around 70mA.
With 4400? base resistor, it was beta challenged.
With 2200? it was good (approx. 2 mA IB)
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

ceci0

Thanks again for all your help!

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