I'm going to design a small wireless sensor box for a weather station project. This involves:
- A sensor running at 3.0-3.6V (1mA)
- A MCU, running at 3.0-5.5V
- A 433MHz transmitter which takes about 6-12V. The higher the voltage, the wider the range. Maybe, 9V is enough. (unknown power consumption)
As the power consumption should be as low as possible, the MCU will sleep most of the time (consumes <1µA) and wake up from time to time (consumes in the order of mA or 10mA). It will power-on the sensor and the transmitter, do its job, and go to sleep again.
The point is how to power this. My ideas:
A high voltage battery directly powering the transmitter, and a regulator generating the MCU / Sensor power. This is cheap and simple, but I doubt it's a good idea: Is a regulator for this low currents efficient/feasible? Pro: works from a single battery.
A low voltage battery to power the MCU. But one needs to step-up this voltage for the transmitter, which makes the circuit more complex.
A high voltage and a low voltage battery to power MCU and transmitter separately. Could also be two low voltage batteries, and the transmitter uses both in series. But this needs a larger number of batteries...
So my question is: what's the best / standard way to power several parts with different voltage needs in a low-power device?