Laser for sending music over a distance

Light is a very popular means of communication. Today, optical fiber communication is the backbone of telecommunication and internet. Light is guided through a fiber optic cable in such systems to achieve low-attenuation and high speed data transmission. Question is: Is it possible to use light for communication without a guiding medium? The answer is positive. Because of the highly collimated nature of the laser beam, it is feasible to use a laser output to transmit information without a guiding medium even in daylight, provided that the line of sight occurs between the sending and receiving units.

Armand & Victor from DIY Experiments Youtube channel illustrates a very simple example of modulating a laser diode output with an analog audio signal and sending it over a distance of more than 400 meters. The laser diode used in this project was of 250 mW capacity, which is ~ 100 times more powerful than a regular laser pointer. A single-transistor class-A amplifier circuit was used to amplify the audio input signal prior to use it for modulating the laser output light. A 1:25 turn ratio transformer is used as a coupling device between the audio and the laser module. The transformer is necessary to ensure only the AC variations (and blocks any DC component) in the audio signal will modulate the laser beam.

Circuit setup for modulating Laser with an audio signal

Circuit setup for modulating Laser with an audio signal

On the receiving end, the audio is reconstructed back by aiming the modulated laser beam at an array of four mini solar panels. The solar panel output voltage varies according to the signal variation contained in the laser and is directly fed to a high power (250W) guitar amplifier. The audio quality was quite remarkable for such a simple setup. Check out the following demo video of this project:


DIY USB 5V Solar Power Bank

Abdulgafur tipped us with his latest project, a 5V solar powered power bank. The circuit consists of two stages, the first stage is the battery charger stage based on MCP73831 and the second stage is the step up converter based on LT1302-5 which converts the battery voltage to 5V.

Solar energy is renewable, free, widely available and clean form of energy. It is considered as a serious source of energy for many years because of the vast amounts of energy that is made freely available, if harnessed by modern technology. Many people are familiar with so-called photovoltaic cells, or solar panels, found on things like spacecraft, rooftops, and handheld calculators. The cells are made of semiconductor materials like those found in computer chips. When sunlight hits the cells, it knocks electrons loose from their atoms. As the electrons flow through the cell, they generate electricity. In this project, we are building a power bank which harvests energy by using a solar panel.

DIY USB 5V Solar Power Bank – [Link]

LipSync – An Assistive Device For Smartphone Use

Smartphones and mobile devices are diving deeply in our lives and make a lot of things much easier than before. So, having a smartphone or a mobile device became one of life’s necessities for everybody. But unfortunately, there is still a big challenge for people with limited use of their arms to use and benefit from these devices.

A group of developers tried to help these people and increase their accessibility to the smartphones through “LipSync”. It is an Arduino-based assistive device which aims to increase the ability to use touchscreen devices through a mouth-operated joystick with sip and puff controls.


The developers team, as they mentioned in the project page, focused on creating a robust and easy to build device, designing a device housing which can be 3D printed, and making it flexible for a variety of wheelchairs.

LipSync is based on Arduino Micro, a microcontroller board based on the ATmega32U4 equipped with a Bluetooth module for connecting with the smartphone and send the appropriate instructions.

Arduino Micro - Image courtesy of
Arduino Micro – Image courtesy of

Two main sensors were used in this project. An Analog 2-axis Thumb Joystick used to manipulate a cursor on the device screen, and a Pressure Sensor to catch sip and puf controls and simulate the actions of “tap” and hitting the back button, respectively.

MPXV7002DPT1CT-ND Pressure Sensor - Image courtesy of Digi-Key
MPXV7002DPT1CT-ND Pressure Sensor – Image courtesy of Digi-Key


In addition to the main control functions, move the cursor, tap, and go back, this device can simulate additional secondary functions such as “tap and drag” and “long tap and drag”.

LipSync is an open source project. Schematics and PCB files are available here, but the 3D printer files and arduino code will be made public later.


To read more details about LipSync visit the project page on, where you can follow it and join the development team.

Save Your Food with Arduino Freezer Temperature Sensor

“Arduino Freezer Temperature Sensor” is an Arduino based project which works as an indicator to notify you when the freezer isn’t work properly. This project was created by “John Saunders”.


To make this project, you will need these parts:

What it is needed is to connect Arduino board , temperature sensor and LED all together. The sensor must be connected to an analog input port, and the LED to a digital output port as shown the figure below:


TMP36 is an easy to use temperature sensor with −40°C to +125°C operation range. It has three pins, supply voltage, output voltage, and ground. The input voltage can be between 2.7 and 5.5 V, so we can connect it with the 5V pin in the Arduino. The output voltage is 0.5V for (0°C) and increases by 10 mV/°C. Here is the full Datasheet.


The next step is preparing the code and uploading it to the Arduino board. The code reads the analog value on its pin, and then convert it to the matching temperature degree. If the temperature is in the normal range, the LED will be on, but if it goes above the threshold, the LED will be turned off.

You can download the code file from here.

Watch this step by step guide:

Rubidium Disciplined Atomic Clock


Cameron Meredith build a real-time-clock module controlled by a rubidium frequency standard, and since it also includes a GPS clock he can track local time dilation effects by comparing the two.

An I2C multiplexer board allows for more than one RTC module (Since these have a hard coded I2C address you can normally only use one). I went for three – One tracking GPS time, another tracking the rubidium standard, and the last one as a control or reference clock – without compensation.

An arduino knock-off compares the relative delay between the pulse-per-second outputs from the Rubidium standard, Real Time Clocks, and GPS.

After some defined time divergence, the RTC aging compensation register is updated to refine or maintain overall agreement. Essentially herding the RTCs so that their output stays within bounded agreement with the Rubidium standard and GPS.

Rubidium Disciplined Atomic Clock – [Link]

Keep Tabs on the Devices Connected to Your LAN


Would you like to monitor all the devices connected to you LAN. Then you can do it using a Rasberry Pi Zero and a few LEDs.

Like most people, we have tons of things connected via WiFi to our router.  Be it AppleTVs, Rasberry PIs, Amazon Echos, weather stations, overhead airplane trackers, security cameras, etc. etc. etc….  The problem arises when you think and expect a device to “work” and it doesn’t.  Is it the device? Is it the service being accessed? VNC server not running?  Most of the time “all is well“, but if it isn’t it can be frustrating.  Who knew the security camera was down?  Why can’t I VNC into that Raspberry PI?  Most of us have been there and this project helps solve the problem.

Keep Tabs on the Devices Connected to Your LAN – [Link]

Optomyography: A novel approach of detecting muscular signals using optical sensors

Optomyography is a novel, non-invasive, non-contact optical method to measure muscular signals of the human body for diagnosing muscular disorders. It is also considered as an emerging technique for making better human-machine interfaces. Matt, Amrit, and Maneesh conducted an optomyogram experiment at Cornell University to sense the movement of fingers and wrist, and eventually to detect hand gestures. The underlying principle of this experiment is that when you shine an infrared light on a muscle surface, the amount of light absorbed or reflected back depends on the blood volume underneath the skin. Because the blood volume changes with the contraction of muscles, by measuring the variation in the reflected IR light, it is possible to detect the motion of the muscles.

Optomyography for muscle movement detection
Optomyography for muscle movement detection

Their sensor unit consists of an infrared emitter and 4 infrared phototransistors arranged in the form of a wrist band. The infrared light emitted by the IR LED is scattered back and is collected by the phototransistors. An Opamp-based instrumentation circuit further filters and amplifies the phototransistor output to obtain nice and clean Optomygram waveform. The amplified signal then goes to a National Instrument’s Data Acquisition System (DAQ) for further processing.

PC application displays optomygram waveform
PC application displays optomygram waveform

Their team also developed a PC application based entirely in MATLAB. The application provides a nice graphical user interface and also performs sensor calibration. They also implemented a principal coordinate analysis method for the detection of the finger movements. The GUI not only plots the data from the sensor, but also displays which finger of the user was moved. This project was mostly successful and the designers were able to accurately detect the pointer, middle and thumb. However, with adding more sensors in the future, the system performance can be further improved to detect not only all the fingers but hand movements too.

Read More …

A full-featured, portable weather data recorder


Do you wonder how to build a personal weather station with data logging capability? Well, Jesus Echavarria, a electronic engineer and DIY hardware maker from Spain, has shared the details of his design of a very professional-looking, full-featured, and portable weather data recorder that is capable of recording ambient temperature, humidity, and light level into a SD card along with a time stamp. The datalogger is based on the PIC18F2620 microcontroller and has options to be powered with a rechargeable 3.7V lithium battery as well as from a USB port. It also features a Lithium battery charger circuit on board using Microchip’s fully-integrated MCP73832 Li-Ion charge management controller IC that is configured to provide a charging current of ~200mA. Two on-board LEDs provide visual indications about the battery condition, such as fully charged or under charging.


On the sensor part, the project uses HDC1050 for temperature and humidity measurements, and TEMT6000X01 for ambient light sensing. The time keeping is performed using M41T00SM6 RTC chip with a separate back-up power supplied from a coin-cell battery.  Two push buttons and two extra leds used in his design to provide a minimal user interface, and most of the configuration part (like time and date settings) is done through a PC terminal program using a command-line interface. The MCP2221 based USB-UART bridge provides the communication interface between the PC terminal program and the PIC microcontroller. Jesus also shares the design files of the 3D printed case he made for his data logger to get a more professional look.

For more details:

Wireless temperature and humidity monitor for baby’s room


This project describes a DIY wireless temperature and humidity monitor for kids’ or infant’s room using the Arduino platform, and inexpensive and easily available ASK transmitter/receiver modules. On the transmitting end, an Arduino nano senses the ambient room temperature and humidity using the DHT22 sensor and transmits the data to a receiving end Arduino over a 433 MHz ASK RF link. The receiving side Arduino decodes the received bytes and displays the information on a LCD screen. The indoor range of the RF transmission is about 100 ft, which is mostly sufficient for a decent size house.

Wireless temperature and humidity monitor for baby’s room – [Link]

Atmel SAMD21G Sensor Board


Mike Rankin created this tiny sensor board with an ARM Cortex M0+ microcontroller and OLED display:

It’s pretty tiny so a 4 layer board made the whole job easier. The top and bottom are pretty much dedicated for components, layer1 are tracks and power traces, layer2 is a ground plane. Mixing up an internal plane and routing layer was interesting.

Atmel SAMD21G Sensor Board – [Link]