The sender is compact (1.25 sq. inch) and operates from 1.8 to 5.5 V. The module consists primarily of an Atmel ATtiny84A which monitors the inputs and outputs the data. A red and green LED provides visual status.
The sender module has:
- Five analog inputs with configurable triggers
- Digital trigger
- Built-in temperature sensor
- Battery voltage measurement
- Optional CR2032 coin cell holder
- Optional pushbutton to manually activate data transmission
Without any programming knowledge, the sender module can be configured to transmit:
- On power up
- When any analog input goes above a certain value
- When any analog input goes below a certain value
- When any analog input changes by more than a certain amount
- Periodically from 1 second to 18 hours
Configuration is accomplished using a laptop or desktop connected via a standard FTDI serial cable (Adafruit #70).
The sender costs only $2.43 in parts (qty 1000) or $3.50 (qty 10). Think of all the things you can monitor at that price -- in the garage, basement, garden, kitchen, or bedroom.
The sender uses only 18 µA on average. This means it can be installed in small places while running on a coin cell, or can be virtually maintenance free with a pack of AAs.
The LoFi gateway listens to all of the senders and uploads the data to a PC or to the Internet.
OPEN AND EXPANDABLE
LoFi is designed to open up the devices in your house. Keeping with that philosophy, LoFi is designed to be open itself. This will allow others to apply their creativity in delivering compatible variations. The completed project will be under Apache License, Version 2.0, so that you can use any or all, for fun or commercially.
I’m looking forward to seeing the shields that are produced -- prepopulated with specific sensors or connectors. Some companies will target specific appliances (doorbells, sump pumps, garage door openers, garden monitors, model rockets) while others will create different form factors and features (long range transmissions) for the LoFI sender itself.
Most users will employ the module as-is, however it is definitely hackable. With the transmitter detached, an ISP6 cable can be connected to reprogram the ATtiny microcontroller with whatever modifications you want to the open source code. It is written in C using the free AVR Studio 6.2 with avr-gcc.
See the System Design Document for complete license details and tools. There are no third-party licenses or restrictions.
Battery Life Expectancy (1 year on coin cell, 10 years on AA)
Message Delivery Rate (>99% success rate)
LoFi as a Solar-Powered Weather Station (temperature and light levels)
LoFi Detecting Garage Door State (tilt ball switch)
Artist Rendition of Productized Look and Feel (contest requirement)
Sender Schematic (see the System Design Document for more)