Electronic Circuits

The Mysterious Laser Receiver Sensor Module!

This article introduces a laser receiver sensor module available on the web. The module, named “Laser Receiver Module Non-modulator Tube Laser Sensor Module”, comes as a cheap module usually without a user guide. So it is handy to know what it can do, how it works and learning how to interface it to your own projects.

Laser Rx Sensor Module Kit

Potentially confusable legend!

Most first time buyers will get a shock upon the receipt of the packet as the sensor element is included in the packet as a loosy component, and sadly there’s no instruction on how to insert it into the sensor socket of the module. If you follow the legend on the PCB, you will be in trouble because the PCB is actually designed for a temperature sensor module, and hence the legend merely refers to the DS18B20 temperature sensor! So remember to insert the 3-pin sensor into the socket as shown below.

Laser RX Sensor Module with Sensor

A cryptic 3-pin sensor?

The 3-pin sensor is actually a minuscule light sensor (receiver) diode with an integrated amplifier and an open-collector transistor at its output. Output of the module, designed to operate on 5VDC power supply, can only go low (L), and the open-collector transistor inside the 3-pin sensor can sink about 20mA current. The description poor Chinese description “non-modulator tube” actually points the fact that the light sensor can handle any source of light and it’s not like a 3-pin  infrared sensor module (TSOP1838 for example) that only detects an infrared pulse train within a particular frequency band.

You may ask how did I obtain the above information. Frankly, I spent hours and hours on web to unwrap the mystery but finally got decent info from an online Chinese reseller. Now to the cool part – the sensor is known in China as “ISO203 Laser Receiver”. You can see its pin notation in the image provided below.

ISO203 Laser Receiver 3-Pin

Module circuit diagram

Following is the retraced circuit diagram of the “Laser Receiver Module Non-modulator Tube Laser Sensor Module”.

Laser Rx Module Schematic

Module quick test setup

In order to test the module you can use the 5V circuit diagram given below. As you can see the setup consists only one amber LED and its current limiter 10K resistor connected across the output of the module (OUT & VCC).

Laser Rx Module Test Circuit v1

The amber LED remains in lit state, however, in case of the reception of a strong (visible or infrared) light beam, the LED goes off to mark a high-level (H) shift at the output of the ISO203 laser receiver sensor. A simple test mechanism, that’s all!

Next is the random snaps of my quick test setup wired on a breadboard:

Laser Rx Module Test Setup

Laser Rx Module Test Setup

Improved output adapter circuit

Even though you can replace the LED in the previous circuit with a suitable opto-coupler to make an isolated output interface (you can obviously use the module’s logic-level output directly too), circuit diagram of an improved output adapter is also provided here. The circuit wired around the Profoundly honored timer chip can be used as a medium-current, inverting or non-inverting line driver that can sink or source load currents up to 200mA safely.

Module Output Adapter Schematic v1

The given ‘inverted’ configuration, however, gives a low-level (sink) output when the module’s output becomes high, and vice-versa. Nevertheless, it’s easy to substitute the LED (LED1) with an appropriate solid-state relay (SSR) or electromagnetic relay (EMR) to drive an external interface or electric load. It’s possible to wire such relays across the output and ground rails of IC1, as well.

To work this out, you need to understand the role of the timer chip in the presented circuit. We commonly think of the 555 as a timer/oscillator chip, but it’s actually very well suited for simple sink/source driver applications alike the one shown here. When the ‘sensing’ pins (2 & 6) of the chip are taken to a voltage above 2/3 of the supply voltage, the output pin switches low (sink-mode). Then they are taken below 1/3 of the supply voltage, the output pin swings high (source-mode). Further, the sensing pins are voltage sensing and demand rather less input drive current.

Now, another snap from my workbench. This time it’s one candid photograph of my improved output adapter setup wired on the breadboard.

Module Output Adapter Test Setup

Better beam of light

As pointed (and observed) previously, the laser receiver sensor reacts positively not only to laser/infrared light but also to visible light. And for this reason, if you’re planning an exclusive laser-beam based project, you will need to encircle the active face of the sensor with an opaque tube to prevent ambient light from interfering with the sensor.

For the common light-beam source (i.e. the light transmitter), try the “Red Laser Module” or the “Red Laser Diode” available everywhere online for cheap. Both the laser module and the laser diode transmits an intense (5mW) narrow laser beam (650nm wavelength) – a red dot extends up to 10 meters. Since the “5V” laser module comes with all necessary parts soldered onboard, you can use it quickly in your project. But for the laser diode, you must add a suitable current limiter resistor to run it on 5VDC. I tested the red laser diode with a 82Ω series resistor (@5VDC).

Red Laser Module and Laser Diode 650nm

Let’s discuss more

Next in the laser-beam series is an advanced “laser fence” project currently under development. The diy project that uses a modulated laser beam is likely to be available to you all before long. Stay tuned until it sets alight by laser!

Further reading

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