Standalone LED tester

David Cook’s new handy LED tester is based on the LM317L adjustable current regulator and consists of a microcontroller and an LCD to display the forward bias voltage across the LED and required series resistance for operation at the user-specified current and circuit voltage.

DIY LED tester

DIY LED tester

Most projects include at least one LED. Before soldering the LED, how can you determine if the color and brightness meets your needs? After that, how do you calculate the correct value resistor?

Many years ago, I built a handy compact LED testing tool based on the LM317L adjustable current regulator. (You’ll definitely want to click on that link before continuing with this article.) It ended up being one of the most useful tools. In fact, the LED tester sits on a shelf above my keyboard, because I use the tester almost as often as I use my multimeter.

The problem with my original LED test tool is that I need a multimeter to measure the voltage of the LED. And, then I need a spreadsheet to calculate the resistance needed for that LED voltage with a given circuit voltage.

So, I decided to make an improved LED tester with LCD display!

Arduino Infrared thermometer

educ8s.tv has posted another great video tutorial on building an Arduino infrared thermometer using the MLX90614 Infrared temperature sensor, which uses the standard I2C protocol to communicate with the Arduino. The measured temperature is displayed on a Nokia 5110 LCD display shield. The device can measure the temperature of an object without any physical contact and with just facing the sensor toward it from a small distance. It can measure temperatures from -70 degrees Celsius to 380 degrees with an of about 0.5 degree at room temperature.

DIY Arduino infrared thermometer

DIY Arduino infrared thermometer

Demo video showing it in action.

ESP8266 weather station with data logging to Excel

Yves Arbour and Rui Santos describes a concept of building a weather station plus data logger using two ESP8266 modules operating in a server/client configuration. The client ESP8266 measures temperature and other sensor inputs and transmits the data to the server ESP8266, which is connected to a PC through a USB-UART bridge. This ESP8266 weather station records the sensor data to a Microsoft Excel sheet on the PC. They used the Things Gateway PC application by Roberto Valgolio to read/write data to the Excel sheets and to generate real-time graphs of sensor measurements.

ESP8266 weather station

ESP8266 weather station

Prototyping board with built-in power supply

This prototyping board with built-in regulated power supplies was designed by Electro-Lab and consists of four independent DC-DC buck converters based on LM2675-ADJ and generates 3.3V, 5V, 12V and -12V at 1A.

DIY prototyping board with regulated power supplies

DIY prototyping board with regulated power supplies

Prototyping is a useful and powerful method in electronics which lets us analyze a circuit before using it in a system or turning it into a product. In this process we may need a single supply or multiple supplies to power the circuit depending on the type of the application. For example, an op-amp circuit may need a symmetrical supply such as +12V and -12V or a logic circuit may require both 5V and 3.3V at the same time. Some applications may need three or more. This means we should have a bench supply with multiple outputs or multiple bench supplies in the environment. This may not be always possible. This DIY Prototyping Board is designed to provide all the most used supply voltages that a designer will need during prototyping a circuit. The switching power supplies on the board output 3.3V, 5V, 12V and -12V rated at 1A independently. In addition those there are two precise voltage references at 5V and 2.5V provided especially for op-amp based applications.

ESP8266 energy monitor

Brian Dorey designed a standalone home energy monitor using the ESP8266 and a bunch of sensors that to monitor the mains current, the consumption of electric energy, as well as the gas usage. His ESP8266 energy monitor measures the mains current using the iSnail current sensor, which is a self powered AC current transducer that provides a 0-5V dc analog signal proportional to the AC current flowing through it. The output from the current sensor is digitized using the ADS1115 16-bit ADC from Texas Instruments and is fed to the ESP8266 through I2C bus. His electric meter has a blinking LED on the front panel that blinks once for every Wh of energy used. So he monitored the blinking LED to track the energy usage using a phototransistor placed in front of the electric meter.

ESP8266 energy monitor

ESP8266 energy monitor

The software was designed in Visual Studio 2015 using the Visual Micro plugin which allowed us to write the Arduino based code in an IDE that is far more user friendly than the normal Arduino editor.  The code is basically a web server that allows you to view the various data on a web page or return an xml feed with the same data values. The ADC is sampled once a second and stored in an array of 60 samples allowing us to average the current usage over a minute.  Interrupts were used for the gas and electric meter inputs which increment the variables for each meter and then set a flag to tell the main program loop to save the values to FRAM on its next loop.

The values returned on the xml feed are the meter readings for the gas and electric meter, the mains current usage at the time of the reading, the average current value over the last minute and the maximum current value for the last minute.  A web page was also added for updating the gas and electric values for when the data logger is originally set up, and if it goes out of sync with the gas meter due to a power cut.

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