Arduino time attendance system with RFID


A how-to on building a time attendance system with MFRC522 RFID Reader and Arduino from Random Nerd Tutorials:

Before getting started it’s important to layout the project main features:
*It contains an RFID reader that reads RFID tags;
*Our setup has a real time clock module to keep track of time;
*When the RFID reader reads an RFID tag, it saves the current time and the UID of the tag in an SD card;
*The Arduino communicates with the SD card using an SD card module;
*You can set a check in time to compare if you are in time or late;
*If you are on time, a green LED lights up, if you are late, a red LED lights up;
*The system also has a buzzer that beeps when a tag is read.

More details at

Check out the video after the break.

Raspberry Pi GPIO programming in C


Steve Chamberlin has written an article about Raspberry Pi GPIO programming in C:

The Raspberry Pi’s 40-pin GPIO connector often gets overlooked. Typical Pi projects use the hardware as a very small desktop PC (RetroPie, Pi-hole, media center, print server, etc), and don’t make any use of general-purpose IO pins. That’s too bad, because with a little bit of work, the Raspberry Pi can make a powerful physical computing device for many applications.

More details at Big Mess o’ Wires homepage.

App note: How to properly configure unused operational amplifiers


Good read app note from Texas Instruments about configuring unused op amps on multi amp chips. Link here (PDF)

Multi-channel operational amplifiers (op amps) are often implemented in circuits that do not require the use of all channels. Undesired behavior in an unused amplifier channel can negatively impact system performance, as well as the performance of the channels in use. To avoid degradation of both the op amp and system performance, the unused op amp channels must be configured properly.

App note: Current sense amplifiers in class-D audio subsystems


App note from Texas Instruments about output current sensing in class-D amplfiers. Link here (PDF)

Current sensing in audio subsystems are widely used in conjunction with CLASS-D amplifiers for diagnostics or to provide speaker current feedback to the DSP for speaker enhancement to emulate smartamp. The most expensive component in the audio subsystem is the speaker. The impedance of the speakers ranges from 2Ω for subwoofer to a 8Ω for stereo speakers. Exceeding the current flowing through the speakers has a potential to create excessive heat in the voice coil which can lead to permanent damage of the speakers.

Adding the Nokia 5110 LCD to your Arduino data logger

From the comments on our ChipKIT based weather station using BME280 sensor module post, Edward Mallon writes:

A lot of us have ended up at this sensor / screen combination. But I couldn’t afford the extravagance of six dedicated control lines on our little pro mini based loggers.
However with some slight modification, you can drive the Nokia 5110 LCD with only 3 control lines, and power the display from a digital pin

More details

Inside the 76477 space invaders sound effect chip: Digital logic implemented with I2L


Ken Shirriff has written an excellent in-depth look at the 76477 sound effects chip:

The 76477 Complex Sound Generation chip (1978) provided sound effects for Space Invaders1 and many other video games. It was also a popular hobbyist chip, easy to experiment with and available at Radio Shack. I reverse-engineered the chip from die photos and found some interesting digital circuitry inside. Perhaps the most interesting is a shift register based white noise generator, useful for drums, gunshots, explosions and other similar sound effects. The chip also uses a digital mixer to combine the chip’s different sound generators. An unusual feature of the chip is that it uses Integrated Injection Logic (I2L), a type of digital logic developed in the 1970s with the goal of high-density, high-speed chips. (I wrote about the chip’s analog circuitry last year in this article.)

See the full post on his blog here.

Banana Pi DLNA media server


Dilshan Jayakody published a new build:

Couple of months back we decided to create our own media server to store our MP3s and digital photographs. But it gets postpone several months due to unavailability of main-boards and other resources. Finally, after reviewing several prototypes we decided to build our media server using Banana Pi (BPI) and MiniDLNA. Before finalize BPI we checked several main-boards which including Raspberry Pi B+, Orange Pi One and BeagleBone Black. Out of all above main-boards we choose BPI M1 because of its inbuilt SATA2.0 interface, Gigabit Ethernet port and availability in local market.

See the full post on his blog here.

SI5351 VFO project


Dave Richards (a.k.a. AA7EE) has a nice write-up about building another Si5351 VFO project:

To many, this will be just another Si5351 VFO project, with nothing to distinguish it from the others. In fact, that’s exactly what it is. The “how to” of connecting an Arduino board to an Si5351 board, wiring up a display, and loading the firmware, is straightforward, and well established. To me though, it was a complete mystery.

See the full post on his blog here.