Components for PWM high current IR LED circuit. BJT, Mosfet or AND Gate?

[mozw]

Hi, I'm trying to quickly build a one off IR remote control for an unusual piece of equipment because the original got broken a couple of days ago. I found Nick Gammon's code on here:

How to create a 38 Khz pulse with arduino using timer or PWM?

I want to create a square wave of 38 KHz to be fed to an IR led. One way is to make a pin high and low for 13 microseconds each. But I can not use that approach since this requires use of loop function. My program is rather big and I would not be able to handle the complexities of doing other tasks as well as creating this 38 Khz wave both in loop() (if it can be done at all) My question is, is there a way, by using a timer or something else to achieve this purpose? So that I can just start t…

which I'm using for the carrier output on D11 on an Arduino Nano and was going to output the modulated control signals out on D6. I was hoping to connect things up roughly like the diagram below:

and use a couple of transistors to enable me to drive around 150mA through the IR LED.

I've got IRFZ44N's, PN2222A's, 2N3904's and a couple of SN74HC08's available all as options to combine the PWM and modulated signal but I'm not sure what I'm better off using? I want to keep to at least the 150mA current for the TSAL6100 LED's I have. The carrier frequency is 38KHz as per Nick's code.

I would have used IRRemote or IRLib2 but I can't find a corresponding protocol. It's similar in timings to a Sony but the commands are much shorter, and I can't make head or tail of sending raw codes (I only need four commands) in either library. It's basically a 2500us header, 600us gaps, 1200us long and 600us short pulses at 15 or 24 bits.

If anybody can help it would be much appreciated, I've spent two days on trying to figure the remote libraries already and need something operational by Saturday Many thanks

[Smajdalf]

You can use single pin to output the modulated carrier. Just turn the carrier on and off instead of writing the other pin HIGH and LOW. Of course the circuit shown should work too.

[mozw]

"Just turn the carrier on and off"

Using Nick Gammon's example code, how would I do that? I'm not too familiar with writing directly to the registers and the code just sets up a reasonably accurate carrier on timer 2. I'm not sure how I would switch that on and off in the main loop?

If I end up going for the circuit I've shown above, which of the available components I have are recommended? Or do I stick both pin outputs directly on to the AND gate and then drive the MOSFET? I presume the other transistors would draw too much current from the AND gate (max 25mA on the datasheet)?

[Smajdalf]

Simplest way using a BJT is pinMode INPUT/OUTPUT.

[Wawa]

I would limit the current 100mA, and use two LEDs in series.
And the constant current circuit shown on this page.
Q1 2N2222
Q2 2N3904
R1 220ohm
R2 5.6ohm
Leo..

[Wawa]

@mozw

I'm not too familiar with writing directly to the registers and the code just sets up a reasonably accurate carrier on timer 2.

const byte IR_LEDpin = 11;

void setup() {
  pinMode (IR_LEDpin, OUTPUT);
  TCCR2A = _BV (COM2A0) | _BV(WGM21);
  TCCR2B = _BV (CS20);
  OCR2A =  209; // 209 = ~38kHz
}

void loop() {
}

@mozw

I'm not sure how I would switch that on and off in the main loop?

Would like to know that too.
Leo..

[jremington]

@mozw

I'm not sure how I would switch that on and off in the main loop?

If the LED is off, no need to do so. But you can disconnect the timer from the port pin by clearing the COM2A0 bit, and set the pin to INPUT.

  TCCR2A &= ~(1<<COM2A0);

[Smajdalf]

@jremington

clearing the COM2A0 bit, and set the pin to INPUT

clearing the COM2A0 bit, or set the pin to INPUT