DIY ECG with 1 op-amp


A DIY ECG made from single op-amp (LM741) and 5 resistors by Scott Harden:

I made surprisingly good ECG from a single op-amp and 5 resistors! An ECG (electrocardiograph, sometimes called EKG) is a graph of the electrical potential your heart produces as it beats. Seven years ago I posted DIY ECG Machine on the Cheap which showed a discernible ECG I obtained using an op-amp, two resistors, and a capacitor outputting to a PC sound card’s microphone input.

DIY ECG with 1 op-amp – [Link]

PCB layout tips for thermal vias


Paul Rako @ discuss about thermal PCB layout tips.

Texas Instruments’ WEBENCH is a neat program, especially because it has Mentor Graphic’s FloTherm built in to help you see the hot spots in switching regulators. This is what taught me that a modern buck regulator will have more heat coming out of the catch diode than the pass FET. It made perfect sense once I saw the heat diagram. After all, a diode has 0.6 to 0.9V across it, while a modern FET has such low on-resistance it hardly drops any voltage at all.

PCB layout tips for thermal vias – [Link]

Space Invaders FPGA Game


Patsiatzis Nikos and Katsaros Nikos build the space invaders game using a ZedBoard FPGA. The project’s code is available on github.

This two person project was completed through the course of Embedded Systems at the University of Thessaly, Department of Computer Engineering. In the context of this game we implemented the classic space invaders game using a zedboard fpga. The code is in Verilog and you can find it on github . The project consists of 3 parts. First the connection with the monitor through the vga interface, the game logic and the sprite memory modules.

Space Invaders FPGA Game – [Link]

An isolated analog input for Arduino

VF1 isolated converter

Giovanni Carrera designed a circuit that accepts input voltage from about 20mV to 5V or a current of 4 to 20 mA and converts it to a isolated frequency signal.

A voltage to frequency converter can realize an opto-isolated analog input for Arduino or other microcontroller systems. This circuit is particularly suitable for industrial control plants with 4-20mA sensors.

An isolated analog input for Arduino – [Link]

How to Measure LUX With Arduino


In this tutorial uses the Adafruit TSL2561 sensor to measure LUX with Arduino.

The TSL2561 luminosity sensor is an advanced digital light sensor, ideal for use in a wide range of light situations. Compared to low cost CdS cells, this sensor is more precise, allowing for exact lux calculations and can be configured for different gain/timing ranges to detect light ranges from up to 0.1 – 40,000+ Lux on the fly.

How to Measure LUX With Arduino – [Link]

CIRCUIT WIZARD – Circuit Simulator for begginers

Circuit wizard is one of the good simulators for beginners. Here the tutorial explains how to draw and simulate a circuit in circuit wizard simulator

CIRCUIT WIZARD – Circuit Simulator for beginners – [Link]

How to Set Up WiFi on the Raspberry Pi show us how to setup a Wifi dongle using SSH connection.

Now I’ll explain how to use that SSH connection to setup a WiFi dongle so you can run your Raspberry Pi wirelessly from a remote desktop application. This is a really useful way to set up your Raspberry Pi, because you will be able to access your it over the internet from anywhere in the world. You can use it from your iPhone, iPad, or Laptop from anywhere with an internet connection.

How to Set Up WiFi on the Raspberry Pi – [Link]

Soft Latch Power Switch Circuit

Dаvid Jones through his Youtube channel EEVblog described in detail how to design a cheap soft latch power switch circuit, using one push button switch to toggle your circuit power on and off with the following design requirements:

  1. Zero power when off.
  2. One on/off switch.
  3. Standalone(no MCU).
  4. General components only (Diodes, Transistors, ..ect).
  5. Minimal parts.

First Basic Circuit


A passing transistor is between the input and the output, with another latching transistor.

When we initially power on the circuit, it will be off because the passing transistor is off and so the latching transistor is off (like the egg and chicken). When we turn on the “ON” switch, the passing transistor is on, so the current flows from input to output and therefor the latching transistor is on. To turn it off, press the “OFF” button and the latching transistor is off, and the passing transistor is off.


First design uses 2 switches and we are looking forward a circuit with one switch only, so let us get a look to the next circuit design.

Second Circuit


When we push the button, the transistor connected to the gate of passing MOSFET will be on, and therefor the passing transistor will be on, on the right side the BJT will be on driving the line down to ground. So next time when you press the the button the transistor connected to gate will be off.

The capacitor connected to base of right side transistor is used to prevent the oscillating on/off while the pressing of the button needs milliseconds and the transistors works much faster.

To see an experiment of the design and to learn more details, check David’s video bellow:

New Alcohol Monitoring System from University of California, San Diego

A new alcohol monitoring system from UCSD consists of a temporary and one-time use tattoo that clings to the human skin and a flexible electronic board that attaches to the tattoo magnetically transfers the results of sensing the blood alcohol concentration via Bluetooth to a smart device paired with it.

The UCSD researchers tried to design the system in a less bulky and less expensive approach. The device uses an electrochemical sensor to measure ethanol molecules emitted through our skin.


To know more about the results of using this device and how this electrochemical sensor works, read the paper published in ACS Sensors journal.


OpenCellular – An Open Source Wireless Access Platform From Facebook

Promised projects from Google and Facebook may change our world connectivity. We saw previously Loon project from Google and the Internet drone Aquila from Facebook.

Facebook this time is trying to find a general solution to improve the connectivity infrastructure. The project called OpenCellular.

This new project is a software-defined wireless access platform, and this gives it the ability to support everything from 2G to LTE networks.


The system consists of general-purpose and base-band computing subsystem with integrated power and housekeeping system and a RF with integrated analog front-end. According to the announcement, Facebook plans to open-source the hardware designs to public, along with necessary firmware and control software.

OpenCellular designed to have various power sources: PoE (power-over-ethernet), solar, DC, and external batteries and internal battery (lithium-ion).


The problem which Facebook try to solve in this new project is to extend network access in both rural and developed communities. The ecosystem cellular networks still constrained, where the infrastructure is very expensive, making it difficult to deploy it everywhere and for smaller organizations or individuals.


OpenCellular still under lab tests; “we are able to send and receive SMS messages, make voice calls, and use basic data connectivity using 2G implementation on our platform.” according to the announcement.

Via: Facebook