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Resistor rating for IR LED for WiFi IoT remote

ntewinkel

Hello!

I was pondering this, and searching into the webs and on the lines, and then realized I have this awesome community of smart people here that probably already know the answers!

Short version:
Are 1/4 watt resistors enough to pulse an LED at 1 amp for an IR remote?
The LED is rated for 100mA continuous, 1.5 amp peak, and 1.6v forward voltage max.
I used an online calculator to figure out that with a 5v supply, a 6.8 ohm resistor will give it a 500mA current, and 3.4 ohms gives a 1amp current.

I'm not sure how to calculate the current on that LED - is it 1.6 volts x 1 amp? or 5 volts x 1 amp?

Either way though - even just the 1.6 watts is 6 times the current rating of the resistors I have. Is that ok for pulsed use for remote control like that?

Should I be using a set of parallel resistors instead (knowing I'll have to up the resistor values to compensate) ?

Project details:
My heat pump is kinda noisy, so at night we set it to "night mode" which is the quietest fan setting it has. We can't keep it at that setting because it won't heat the house well enough, so in the morning we turn the temperature up a few degrees and set the fan to "automatic".

I've been trying to automate this process, because the heat pump remote is kind of annoying in that you have to step through all 5 fan speeds to get back to Automatic.

I bought a little WiFi IR remote off Amazon a few years ago, which is ok for turning the heat up in the morning, but it only supports 3 basic fan speeds, so it doesn't properly turn the fan down at night. I recently bought another similar newer unit, hoping that after a few years my Daikin heat pump would now be fully supported, but it's still the same. Frowning2

But there's hope! I found a Github repository that actually fully supports my Daikin heat pump codes! And for my favourite IoT micro-controller even - the Wemos D1 Mini.

Using a basic IR LED I had scavenged from something in the past, I was able to get it to work, but the IR LED range was just -barely- able to reach the heat pump when aimed just right (I realize now that I was using far to big a resistor value).

So I got a few new "high power" IR LEDs (the clear QED234 ones) from element14's shop, which I hope will give me the range I need. Then I did the aforementioned calculations to find the ideal resistor values to get some good oompf out of the LED to reach further.

I was just about to start soldering things up when I realized that 1amp of current is higher than the 1/4 watt rating of the resistors I have.

I'm hoping you'll have some good advice for this software-biased hobbyist Laughing

Also - I'm guessing a resistor failure would generally not cause a short? (ie, losing a resistor is ok, I have plenty more - losing an IR LED is tougher as I only have a few!)

Thanks!
-Nico

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    Some good info already in the answers. It is high temperature that would kill the resistor or LED, and even 1 Watt in a component that size will heat up quickly. You would need to determine how much energy and time it takes to reach a dangerous temperature. Then you could figure out how to keep the components cool enough for the time you need them to operate.

    I would just keep the power down in each component simply to avoid temperatures that could burn you or melt plastic. The components will last longer and the calculations are much simpler. You could use several resistors in parallel as you mentioned, or LEDs and resistors as Frank mentioned. Wolfgang's calculations indicate you might get away with 2 LEDs with 2 resistors on each LED.

    If you can find a cheap lens that will work at the wavelength of your LEDs, it could substantially improve range without having to boost power. I once used an 8 inch lens to make a 0.16 Watt LED visible from one mile away.

    One other note is the driving transistor may need a strong drive (low impedance source) to keep up with the switching rate. This could mean adding a second transistor.

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  • 0

    Some good info already in the answers. It is high temperature that would kill the resistor or LED, and even 1 Watt in a component that size will heat up quickly. You would need to determine how much energy and time it takes to reach a dangerous temperature. Then you could figure out how to keep the components cool enough for the time you need them to operate.

    I would just keep the power down in each component simply to avoid temperatures that could burn you or melt plastic. The components will last longer and the calculations are much simpler. You could use several resistors in parallel as you mentioned, or LEDs and resistors as Frank mentioned. Wolfgang's calculations indicate you might get away with 2 LEDs with 2 resistors on each LED.

    If you can find a cheap lens that will work at the wavelength of your LEDs, it could substantially improve range without having to boost power. I once used an 8 inch lens to make a 0.16 Watt LED visible from one mile away.

    One other note is the driving transistor may need a strong drive (low impedance source) to keep up with the switching rate. This could mean adding a second transistor.

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