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.
There are many indoor temperature and humidity meters and loggers already built. But there is always a space to do something new and useful in this area. Davide decided that measuring temperature and humidity isn’t enough for complete climate meter, so he added CO2 meter.
His project consist of NDIR infrared MZ-Z14 CO2 meter, DHT22 temperature and humidity sensor. Atmega328 reads sensor data, displays it on LCD screen and also logs to xively.com feed. Connection to internet is established with network board based on EC28J60. Where most of project code he brought from his previous projects.
Imagine that you need to flash hundreds of microcontrolelr chips. One way is to do this one by one, but this can be exhausting task and plus inefficient. If you use standard ISP adapter your boards has to be with ISP headers soldered on- this also rises overall cost. So how to do this faster and efficient. If you have a CNC platform lying around, it may be fairly easy.
Pleasantsoftware shared his rig where he managed to set up an automated solution of AVR flashing. He needed to flash several hundred of AVRs so building this rig seemed quite reasonable. On his boards he used special programming connector which sits on SMD chip directly to ISP and power pins. Assembled PCBs come in panels of 40. All he had to do is to build a programming connector holder which was 3D printed. He used his G-Code sender app to send position commands to CNC. Hex code and fuses are hard coded in to source since it is same for all batch. Single panel of 40 AVRs are flashed in 10-12 minutes. I doubt that this can be done manually and still be enthusiastic about this.