SensingRebuild shelfUnplug and unscrew

Infrared LED

Also called IR emitter, 940 nm LED, remote LED.

The clear or dark LED in a remote control. Typically 940 nm. Invisible, so a phone camera is the test instrument. A remote LED expects pulses, not a DC current from a 9 V battery.

If you are new to this category

A sensor reports a condition such as weight, light, temperature, or position. Many sensors do not switch fully on or off. A kitchen scale bar, for example, changes by thousandths of a volt. Keep the small board that read the sensor if you still have it.

Keep the connector. Write down the wire colors before you cut them. If you do not know which wire is which, the sensor is hard to reuse.

Four wires on a scale sensor

Red and black feed the sensor a steady few volts. Green and white are the tiny signal, measured between them, not from either one to ground. Pressing the bar changes that signal by millivolts. A normal meter on DC volts can show that it responds. Turning it into a number on a screen wants a small amplifier board, often an HX711.

Specification. The right-hand column is what is typical. The label on the part in your hand wins if they disagree.
What to look for	Usual figure
Wavelength	About 940 nm for remotes. 850 nm exists and looks different on a camera; it is less common in remotes.
Drive	Pulsed tens of mA. A series resistor is not optional.

Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.

What people actually use it for

A remote you are rebuilding
An optical interrupter illuminator
A short night-vision illuminator

Leave this one when

You already destroyed the lead frame getting it out of the rubber. Remotes are worth more as remotes.

Buying a new one is the better idea when

A known 940 nm LED. They are cheap. Pull one when the remote is already dead.

How to tell if this one still works

Diode test, then a few mA, then look at it through a phone camera. It should glow on the screen.

Tools you will want: Meter, Phone camera, Resistor.

Words on this page

Short meanings, so the rest of the entry is readable if you are not already doing this every weekend.

series: Connected in a chain. Cells in series add their voltages. LEDs in series all go dark if one of them opens.

Where people actually find it

4 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.

Harvest at a glance
From	Call	How many	How often	Where it sits
Infrared remote	Prize	1	always	The nose.
Garage door opener	Prize	1	usually	The other beam.
LCD television	Bonus	1	usually	In the remote that was sold with the set. It is usually in the couch, not the TV.
Photoelectric smoke alarm	Bonus	1	usually	The sense chamber.

Prize — take this firstInfrared remote1 · always
In this particular machine
940 nm class, pulsed by the board.
Where to look
The nose.
How to get it out
A working remote is more useful than the diode.
The condition to expect
Good if the remote still flashes on a phone camera.
Prize — take this firstGarage door opener1 · usually
In this particular machine
The emitter.
Where to look
The other beam.
How to get it out
Do not swap the pair's polarity.
The condition to expect
Good.
Bonus, if you are already in thereLCD television1 · usually
In this particular machine
A 940 nm diode. A working remote is more useful than the diode.
Where to look
In the remote that was sold with the set. It is usually in the couch, not the TV.
How to get it out
The remote is its own donor.
The condition to expect
Leaked button cells are the usual remote failure.
Bonus, if you are already in therePhotoelectric smoke alarm1 · usually
In this particular machine
A paired IR LED and photodiode in a maze.
Where to look
The sense chamber.
How to get it out
The maze is the smoke detector. The parts are ordinary.
The condition to expect
Good.