IR Sender

What it is

An infrared LED and the transistor that switches it. There is no oscillator and no chip: your microcontroller makes the 38 kHz carrier by switching SIGNAL, 21 times inside every 560 µs mark of a NEC frame.

The LED is an Everlight IR908-7C, a sidelooker that shines out of one side of its clear package. It lies flat with that side facing up, so the beam leaves the parts side of the board. The beam is 40° in all, ±20° off axis, half the receiver's ±45°: the sender is the half you aim.

Where the current comes from

SIGNAL does not light the LED. It puts a couple of milliamps into the transistor's base through 1 kΩ, and the transistor lets VCC push current through the LED and its 150 Ω resistor:

Reach follows the square root of current, so 5 V buys about a third more range than 3.3 V. Both currents are inside the LED's 50 mA rating. Keep VCC at 5 V or below: the resistor is the only limit.

Which pin is which

Parts up, header at the bottom, left to right:

SIGNAL is active HIGH, the opposite of the receiver, and IRremote's default, so nothing needs setting. The back prints TK16 IR REMOTE SENDER instead of pin names; the square pad, on the right from the back, is GND.

Wiring, in three lines

1. GND to your board's GND.
2. VCC to 5V (VBUS on a Pico) for range; 3V3 works.
3. SIGNAL to a digital pin: D3 on an Uno, GPIO 22 on an ESP32, GPIO 6 on an ESP32-S3, GP17 on a Pico.

Leave NC unconnected.

Example

Sends one NEC code every two seconds. The address and command are placeholders: put in numbers you read off your own remote with the TK15 receiver, because there is no table to look them up in.

#include <IRremote.hpp>   // IRremote by shirriff, z3t0 and ArminJo

// Uno: 3. ESP32: 22. ESP32-S3: 6. Pico: 17.
const int IR_TX_PIN = 3;

const uint16_t ADDRESS = 0x04;   // REPLACE: from your own remote
const uint8_t COMMAND = 0x16;    // REPLACE: from your own remote

void setup() {
  Serial.begin(115200);
  IrSender.begin(IR_TX_PIN);
}

void loop() {
  Serial.flush();        // on an Uno, no interrupt mid-frame
  IrSender.sendNEC(ADDRESS, COMMAND, 0);   // 0 repeats: one press
  Serial.println("sent");
  delay(2000);
}

# mpremote mip install "github:peterhinch/micropython_ir/ir_tx"
# Sending works on an ESP32 or a Pico; not on an ESP8266.
import time
from machine import Pin
from ir_tx.nec import NEC

# ESP32: 22. ESP32-S3: 6. Pico: 17.
IR_TX_PIN = 6

ADDRESS = 0x04                   # REPLACE: from your own remote
COMMAND = 0x16                   # REPLACE: from your own remote

nec = NEC(Pin(IR_TX_PIN, Pin.OUT, value=0))   # LOW: LED off
while True:
    nec.transmit(ADDRESS, COMMAND)
    print("sent")
    time.sleep(2)

Where to start

The TK16 shares its handbook with the receiver, because nothing you send is useful until you have read a code off a remote. It is shelved on the IR receiver's page. The two chapters about this board are the sender, pin by pin, the transistor and what the supply decides, and be the remote, which sends a code you captured.