When nothing sees it
Start with the red LED. It is on the infrared LED's transistor, so it splits every fault in two: dark means SIGNAL, VCC or GND; lit means the infrared LED is on, and the problem is the camera, the carrier, the aim or the room.
The red LED first
The red LED hangs between VCC and the same transistor as the infrared LED. It lights only when SIGNAL went HIGH, VCC and GND arrived, and the transistor switched. So before a camera, a receiver or any code, run the first blink and watch it.
Pick what you see.
Dark: the block, or the wires to it
A dark red LED means the transistor never switched or the LEDs have no
supply. The usual causes are a wire on NC instead of SIGNAL, IR_PIN naming
a different pin from the one wired, or a missing pinMode(IR_PIN, OUTPUT).
Count from the square pad: GND, VCC, NC, SIGNAL.
Lit: the light, and where it goes
A lit red LED means the infrared LED is on. The block is working, and the fault is in what is meant to see it:
- A camera may filter infrared. Try another, the front one included, looking straight into the lens.
- A TK15 hears only 38 kHz bursts. A blink sketch never reaches it; send with IRremote, and keep the two blocks about 30 cm apart.
- A TK64 sees steady light, the room's included. Face it to the LED and keep the sun off it.
- The aim. The beam is 20° across. A few degrees off costs a lot, and a pale wall nearby can bounce more light than the direct path.
Range
On 3V3 the infrared LED gets about 13 mA; on 5V about 24 mA, for about a third more reach. That is one wire, and the pin does not change. Past that, the range comes from aim and from keeping bright light off the receiver, not from the block.
When it does not work
The transistor is not switching, or the LEDs have no supply. Count from the square pad, GND, VCC, NC, SIGNAL, and check VCC goes to 5V or 3V3 and GND to GND. Then check IR_PIN in the sketch names the pin SIGNAL is on, and that setup() calls pinMode(IR_PIN, OUTPUT).
The infrared LED is on too: they share the transistor. What is left is outside the block. A TK15 needs 38 kHz bursts, not a steady beam; a TK64 needs to face the LED; a camera may filter infrared out. The beam is only 20° across, so check the aim first.
Nothing on the board holds the transistor off, so it follows the pin during reset. Use the book's pins, none of them strapping pins, and set the pin LOW first in setup(). The flash of light does no harm.
No. VCC only feeds the two LEDs, and the transistor keeps it away from your pin. 5V is what this book recommends. What the block does not survive is more than it was built for: keep VCC at 5 V or below.
The 38 kHz carrier, NEC codes, and a remote that works across a room.
The receiving half: the TK15 IR Receiver, and the IR handbook →Edit this page — content/books/ir-transmitter/when-nothing-sees-it.mdx
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