Laser module, KY-008

A 650 nm red laser diode in a brass barrel on a three-pin board. Aliases: KY-008, laser transmitter module, laser pointer module.

The diode and its resistor sit in series between S and GND, so the signal pin is the supply: a pin driven high runs the laser, low turns it off, and analogWrite() dims it. On most of these modules the middle pin is not connected to anything.

Pins

Pin	What it does
S	High lights the laser. The current comes from this pin.
VCC	The middle pin. Not connected on most modules, and not in the model.
GND	Ground.

Properties

resistor is the resistor in series with the diode, 100 ohm by default. The boards are sold without a schematic, so the value is an assumption; with it a 5 V pin runs the beam at full brightness and a 3.3 V pin at a little over half.

While it runs

Nothing to drag. The beam leaves the barrel and ends in a red dot, as bright as the eye would see it, so a PWM-dimmed laser draws a dimmer beam.

What the model gets right

The supply is the signal. There is no driver on the board: the diode's current comes from S itself, the way it does on the real module.

Dimming. The brightness follows the average of a PWM signal, as an eye sees it.

What it does not model

The lasing threshold (a real diode below it glows dimly instead of lasing), the light's power, and the beam's spread.

Safety

A real KY-008 is a Class 3R laser. Never point it into anyone's eyes, a pet's included: a cat toy keeps the dot on the floor.

Common mistakes

Wiring the middle pin and leaving S on a fixed 5 V: the laser is then always on, and the sketch has nothing to switch.

See it in action

Cat laser toy swings the laser around the floor on two servos for a minute at a press of a button. Open it at /templates.