When I finished my Master Unit for Home Control, I want to attach some Wireless sensors via 433MHz Protocol. (At least 2 ones, 1 for Measuring the outdoor Temperature/Humidity with an DHT22 and Lightlevel and 1 for checking if my mailbox lid opened)
Therefor I need a 433MHz transmitter and it would be nice to be able to programm the IC in-system with another arduino or better with the Arduino USBSerial (after flashing the boot-image inside of and Arduino UNO.
The system should run (stable) on battery and send a signal every x seconds or when some external interrupts happen (like opening the lid)
What parts do I need at least? (except the microcontroller and the 433MHz transmitter) what do I need to look for in circuit design to save as much power as possible? How can I check if the battery goes low (and send an alarm signal)?
Best Answer
I designed a transmit-only device for use in a big freezer department in a store. They used 433MHz and a cheap little PIC micro that woke up about once per minute and transmitted temperature and its battery level to a central collection point for all the local devices. The wake-up time between one unit and the next was about a minute with a bit of variability due to their unique ID codes.
This meant the central receiving unit sometimes got garbage but, in the main it could pick up all the data from up to 100 (I think it was 100) units in about 5 minutes (given collisions were not infrequent.
Battery lasted about 1 year.
The up-time was about 40ms given that the crystal needed about 20ms to stabilize and I suspect that should I have used an RC clock I could have halved this time. The transmission was: -
Hope this helps. Here are a couple of little circuits to get you on your way. They use PICs but the general functionality can be transferred to virtually any MCU: -
They came from here