Turn-key PCB assembly services in prototype quantities or low-volume to mid-volume production runs

AVR RF based bootloader

Sometimes when you deploy your device for permanent use it is not always convenient to connect to it in order to perform software upgrades. Necromant wanted something convenient and cheap that would allow him to connect to AVR without wires. Since he already had several nRF24L01 RF dongles he decided to build so called over-the-air bootloader. He ported Arduino based nRF24L01 library to AVR by removing Arduino dependencies along with few fixes. One RF dongle is attached to target MCU using either hardware SPI or software SPI. Bootloader fits in to 4KB. As programmer, there is a uISP dongle used where nRF24L01 sits on top. Currently programming speed isn’t great which is probably mostly limited by V-USB. Since RF dongles can handle up to 2MBPS speeds there are plenty space for improvements. But rather sticking to AVR, Necromant plans to build another dongle which will be STM32 based USB chip. Continue reading

RF communication channel for microcontroller based devices

Wireless communication is always interesting. First of all it frees us from wires and increase distance between sender and receiver. You can get lot of advanced RF modules like Zigbee, bluetooth, GSM WiFi. But they are more expensive and not always necessary to have simple RF channel. Simple RF modules may do job well. They cost pennies and are pretty easy to work with. Usually they come in frequencies 315Mhz and 433Mhz. These modules dont have any modulators or encoders. They simply modulate and transmit what ever you give to DATA pin. So obviously some data encoding/packeting mechanism is needed. If microcontroller is used simple USART connection may work pretty well. But this is not very reliable way. If you want to free MCU from encoding tasks then there are special encoder/decoder chips (HT12E and HT12D) that takes parallel data from MCU and forms data packet to be transmitted. Receiver decodes this packet and produces same signal on output like they were sent using wires. Bhargav shares with details on how to set up transmitter and receiver with decoders and… Continue reading

RF garage door opener

After Mike moved to his new place, he found that current garage door opener is does not work as expected. So he decided to make his own remote controlled garage door opener. As usual RF link consists of two parts – transmitter and receiver. Building receiving part is easier as there isn’t much restrictions on size and power supply because it always stays inside garage and can be powered with wall wart power supply. So it is based on Olimex AVR-MT-128 development board with LCD. LCD currently displays times the garage door was opened. For RF communications he has chosen cheap 315MHz RF modules. There is more hustle with transmitter as it has to be carried around. It must have decent small size, range and power usage. It is based on Attiny13 microcontroller. As power supply there is a 9V battery used that is scaled down to 5V (wouldn’t call this efficient). Prototype version has proved itself be reliable. Now it time to make it compact… Continue reading

Attiny85 based power meter

Power meters are great tools to measure power usage of any appliance at home. It may help to hunt down energy hungry devices and lower the usage by replacing them with more efficient. Why build an energy meter? The obvious answer would be – flexibility. When you build one – you can add as many features as you like. So here is one of solutions using accessible parts like Attiny85 microcontroller and several other parts like op-amps. Power meter measures voltage, current and so power. Also it tracks frequency and power factor and is able to operate up to 100A loads. There is optional an RF transmitter which transmits data to displays or loggers. Continue reading