For over a year I’ve been working on a project called Mote2 (reads as SquareMote). I haven’t written anything about it until now, because perfectionist in me wanted to finalize it before introducing it to the world.
But year is a long time, so I finally decided to lift a curtain so to speak….
Main idea behind #Mote2 is an ultra-low-power battery powered remote sensor that has as much devices already on board as possible to make it easy to deploy as an independent sensor, but also have ability to expand its functionality with add-on “shields”.
These are main features of the device:
- Onboard 3.3V voltage regulator allows device to be powered by external power source of up to 16V
- 3 Position physical switch that allows to bypass voltage regulator for low voltage source (3V coin cell), use normal power source with voltage regulator or turn power off
- Onboard 3V replaceable CR2032 battery
- Onboard RFM radio transceiver (RFM69W or RFM12B working at 433 or 915Mhz)
- Temperature and Humidity sensor
- ATMega328p processor running at 8 Mhz for low power (can work under 2V)
- Onboard 16Mhz resonator which allows MCU to also work at 16Mhz when low power operation not required
- Onboard LEDs
- Onboard buttons (currently 6)
- Small size (5×5 cm)
- Two 14 pin headers that allow access to all AVR pins
- External power header
Initially this device was meant to be a remote weather sensor for my Xronos Clocks, but it grew into something more.
No need for bulky headers or wires, just insert 3V coin cell battery and drop this sensor where you want to monitor temperature/humidity. Of course it’s not waterproof, so you can’t technically “drop” it anywhere outside.
Long battery life was top priority and under ideal conditions #Mote2 can run for about a year without needing new battery. Of course it all depends on ambient temperature, and frequency of updates. Cold is battery’s worst enemy and slashes it’s life significantly. However in warmer months (from April to November) I had a sensor outside sending updates every 5 minutes without seeing end to battery life in near future.
Few hardware “tricks” were used to lower power usage.
- Battery bypass for Linear Voltage Regulator.
This provides most power saving, as Voltage Regulator created huge drain for power sources below 3.3V
- ATmega328p running at 8Mhz.
This reduced power drain, and also allows chip to run at voltages as low as 1.8V
- TH02 sensor power disconnect.
Temperature and Humidity Sensor’s (TH02) VCC connected to ATMega’s digial pin, allowing to switch sensor on and off at will
This design allow for power usage to be as low as 184nA during deep sleep for example.
Update: I’m not sure where my measurements went wrong, but recently I did another test, and I’m actually getting around 18uA current in deep sleep, so not quite spectacular as 184nA but still I’m getting almost a year of life from single 3V coin cell (during warmer months or inside the house).
Just like Arduino, #Mote2 supports “shields” to expand it’s functionality. As of now I’ve developed two of them:
RGB LED Strip controller and RTC/LCD shield. More are coming!
Other than serving as straight forward weather sensor, #Mote2 is great at other tasks, like home automation.
Here are some project I’ve used it in.
Without any additional hardware (because of built in 6 buttons) it can be used as RF remote control that works at amazing range. I used mine to control solar powered lights in backyard (about 300 feet away from the house).
I’m already working on add-on shield that will allow to use second #Mote2 as receiver and IR blaster to control various AV equipment hidden in cabinets where IR remote can’t reach.
Integration with Z-wave gateway is also on my to do list. This will allow to use #Mote2 as remotes that control various Z-wave devices such as light switches and outlets throughout the house.
My mailbox is pretty far from my house and it’s also on the other side of the road, so knowing when I have mail without physically walking over there (especially in deep snow) can be very convenient.
Using two #Mote2 I build a simple notification system. One #Mote2 serves as transmitter, second one a receiver.
Using a 3D printer I made a very slim enclosure for it so it can fit inside mailbox without interfering with large packages. Sensor is made out of magnet and a reed switch that get’s activated when magnet moves close to it. Magnet is located in the mailbox door, so when it’s opened, magnet moves away from the switch, and when it’s closed magnet moves closer to switch.
Sounds simple enough right? Unfortunately there was one issue. As mailbox is closed most of the time, reed switch will be on, draining a little power from coin cell. When switch is opened there’s no extra drain, and battery life is significantly longer. So I used a little trick by applying second neodymium magnet on the opposite side of reed switch. Both magnets cancel each other’s magnetic filed when placed just right and reed switch stays open (not engaged). As soon as second magnet (in the door) moves away, magnetic balance breaks and stationary magnet pulls on reed switch engaging it.
Thus current flows thru switch only when door is opened.
Transmitter #Mote2 stays in deep sleep, drawing almost no power from battery until it detects that switch changed it’s state. Using hardware interrupt this wakes up the device and transmits message that mailbox was opened (or closed).
For receiver I made a fancy enclosure with LED lighted acrylic sign and piezo speaker for audio notifications. #Mote2 inside receiver, lights up acrylic sign and plays melody. I also programmed it to turn light off when it detects second door opening (when I retrieve mail).
Later on I added second receiver connected to a Raspberry Pi running Moteino Gateway. That one not only shows me when my mail was received via web page, but also sends me SMS or e-mail.
Smart LED Strip Controller
Think of it LED Strip controller on steroids. This add-on shield allows #Mote2 to control 12V RGB LED strips and adds connectors for devices such as motion detection (PIR), Light Sensor, Button and IR receiver.
It will detect motion in the room, evaluate ambient lighting and based on that will turn on LED light. Great for closets or stairs. Light will go out automatically when no motion is detected for a period of time. There are tons of parameters and user configurable settings which will define how it will work. You can use IR remote control, or another #Mote2 as RF remote control. And because #Mote2 inside already has temperature/humidity sensor this will serve as additional sensor for your leaving space.
Using laser cut acrylic I’ve made an attractive enclosure for LED controller that can be attached to a wall.
Button has multiple purpose. It can turn on/off light if motion detection is off, and it can also access “menu” system that allows to change colors for example.
Settings such as timeouts, light threholds, etc. are stored in EEPROM so they preserved during power loss, and all these settings can be updated wirelessly.
Weather Monitoring station
Using RTC/LCD Screen shield, makes it easy to plug in color TFT or Monchrome LCD displays to #Mote2 . I’ve used one to receive sensor data from several #Mote2 sensors both inside and outside the house and display it on bright TFT screen.
Shield also has built Real Time Clock IC and buzzer. You can build your custom alarm clock for example 🙂
In conclusion, these are just few projects that possible with #Mote2 . There are many more I plan to implement. These will be things like leak detection sensor, heating oil tank level monitor sensor, radiation monitor, etc. Possibilities are endless.