5V arduino pro mini battery powered - help needed
First off, I want to say that I am loving creating sensors and working with the mysensors api. I recently ran into an issue and was looking for some advice. I currently have been using 5V arduino pro minis as the brains of my sensors and everything is working great. I have built three sensors and am working on two more. The last two I want to make require the use of batteries rather than a wall wart power supply.
I have looked over the page about powering the sensors using batteries but I guess I dont completely understand how to make it work. Everywhere I read mentions they are using the 3.3 V pro minis and I have the 5V models.
Here is was I have available to use:
5V arduino pro mini
4xAA battery pack - outputs ~ 6.5V with brand new batteries
10 1N4001 Diodes - if I put three in series the voltage drops to around 5.5V
I would like to monitor the battery level if possible but at this point I would just like to be able to power the sensor. I dont understand this part at all. Any help would be great.
Thanks in advance.
You could use a 5v volt regulator, and thus get a steady 5v supply.
You could also yank the crystal of the arduinos and use the internal oscillator, which brings the arduino down to 8mhz, and then provide it with 3v3 on the vin pin, this essentially makes it an 3v3 8mhz arduino.
If you power it with 4 batteries and you disable the power led you should get fairly long battery life, regardless of the required voltage of your setup.
If you are uncomfortable with modding your arduinos, I suggest you look in to low dropout volt regulators.
I'd use a DCDC Step up converter (there is a 1-5V to V mentioned in the MySensors shop).
For a 5V device I'd not connect directly to the batteries, because the voltage might drop below 5V although the batteries are still far away from beeing empty. You don't want your approach with the diodes (or any other linear voltage regulator) because it wastes expensive energy to produce heat (In order to get the higher voltage down).
With 3.3V Device I'd (and will in the near future ) try to just use two batteries (without regulator). They'll have 3V max. Voltage and Adrduino Pro mini / nrf24l01 work down to 1.9V - so most if not all of the charge from the battery can be used. (rechargeable batteries shouldn't go below 0.8V so this fits quiet nicely (2*0.85 = 1.9).
Additionally I think it might be easier to use the 3.3 V Arduino over the 5V, because more lowpower people use it and because the power consumption typically drops if you use less voltage as long as we are talking about some mA. E.g. Modern CPUs are working <1V to keep down the (thermal) losses.
As a last sentence: Designing real low power and battery applications is hard work. It is dependet on sofware but also -maybe somewhat more- on hardware. You must design/find a power supply that matches the application very well and have to think of the parts of your sensor/circuit you can / must switch off. Maybe some of them must be switched off in hardware (cut power supply). Then it is part of the software to re-enable them in the correct sequence and with proper startup times to have everything work.
However for a start I'd recommend to try the mentioned ste up converter. But I fear it has a relative large quiescent current because it is able to deliver 500mA which is much. Maybe someone else knows some modules that suit better and have a defined quiescent current.