Numitron tubes are special type of displays, where digits are constructed out of segments like in 7-segment LED displays. They can be driven with standard 74HC595 shift registers. Numitron indicators require about 20mA of current so interfacing them to microcontrollers is fairly easy. Kalshagar have built really nice four Numitron digits based digital clock.
He wanted clock to be modular so that different parts could be reused in other projects if needed. To do so, he split design in to two boards – a display board which carries only tubes and driving circuit; while another part where microcontroller, RTC and backup battery is. He has done several versions of board and enclosure while eventually he stayed with rusty metal casing which looks really great.
When starting new microcontroller based project you start looking for suitable platform to start with. Many times in small projects Arduino takes over because it is popular, simple and have great ecosystem with tons of libraries and project examples. It is hard to beat this, but possible…
Pieter have sent us an update on their development board which runs on Atmega328p microcontroller. It doesn’t follow Arduinoe standards, but rather focus on other things that make easier development and testing. Their scorpion development board have all necessary elements like efficient power regulator, USB-USART bridge, buzzer, 512K dataflash, LED, push button, ADC scale and filtering. The rest of connection interfaces and GPIO are positioned on the side of PCB.
But this is not a board what makes it great. They’ve done great work on building software framework to develop embedded programs clean and efficiently. Firmware library has been developed to be portable between 8-bit, 16-bit and 32-bit systems. Framework focuses on good developing practices that evolved during years of coding. Several great project examples will get you started in no time and in time you will start appreciate the hard work they’ve put in.
Most PCs have have option that enable booting it on keyboard input. This gives ability for interesting hacks like knock enabled PC power up. Joonas have built a simple Attiny45 device that detects knock and sends PS/2 command to PC to turn it on. Knock is detected with piezo buzzer that is used as knock sensor. Since circuit is connected to PS/2 interface, it also provides power supply.
knocks are detected by reading piezo sensor with microcontroller ADC input. ADC is implemented to sense signal level that is over threshold. And in order to to detect three successive knocks there is a timer based counter implemented. This is really simple implementation that can impress your friends.
Music cards are not something new. But those that you normally get play annoying tunes that are low quality. Dmitry thought that he can do better. So he started building his own version of music card. His goals were to have full fidelity playback, random songs each time and be small enough to mimic gift card. To accomplish this he had to solve several problems like playing quality sound with Attiny85 microcontroller. It seems that he’s done this pretty well by generating 64MHz on one timer with PLL which his used to generate PWM based analog output. Another 32KHz timer generated actual music sampling. Music has to be stored in SD card in WAV format. Then they are picked by using uFAT library.
Another issue were music volume. Since Attiny85 could source up to 20mA with 3.0V battery is could provide about 60mW power which is really low. One option could be adding power amplifier, but since signal is digital, he ended up with using full bridge driver out of four MOSFETs. This way he was able to reach 5.8W output signal. Player is powered with 180mA Li-Po battery. Having in mind that battery is a limiting part, he built-in small USB powered charger out of MCP73831. The rest was to put everything in to CD case, add switching mechanism that would turn circuit when its opened and take care of card itself.