Arduino Pro Mini 3.3V / 8MHz operated by a battery.

Projects General Guidance
1

Hello everyone! :slight_smile:

I am working on a project, which requires a portable device. I opted to go for the Arduino Pro Mini 3.3v due to its size as well as capabilities, which perfectly fit the user reqs.

Now, the Pro Mini 5v / 16MHz is also a possibility, however, I would like to have as small and as accessible battery source for the regular user, as possible.

Could you give me any recommendations on what kind and type of battery(-ies) to use?

Initially I was thinking of a CR1616, however, there is a clear lack of power for the Mini alone. Thus, perhaps two AAA batteries? Or a single AAA with a boost converter?

Maybe some of you have already built a similar device, which draws power from a battery to power the Mini.

Any suggestions / comments are greatly appreciated.
Thank you in advance!

2

2 AAs connected to VCC pin would work. Bypasses the onboard regulator, run from 3V directly.
Can also lower the brownout detection fuse to use the battery down to 1.8V, or turn it altogether.
Maybe also consider a 1000mAH LiPo, small flat battery package.

3

I have considered the 1000mAH LiPo, but the surface area of it is not ideal. I'd love to have something a bit more compact. For now, though, it seems like the most viable option...

4

So pick a 500mAH LiPo. You can't get a more compact battery with more capacity per cubic centimeter than LiPo, but you can select the battery size to suit your application. If you can't fit enough mAH in your physical space available, then work on reducing the power consumption.

5

How much charge do you need?

6

Well, the device consists of the following:

-A battery (...);
-An Arduino Mini 3.3v / another possibility is an ATtiny85 chip;
-A bluetooth module (HC-05) - takes around 40mA;
-A temperature sensor (DHT11) - takes 2.5mA max;
-A light intensity sensor (Mini photocell) - uses less than 1mA;
-A soil humidity sensor (YL-69) - operates at 35mA, 3.3V;

Now, the battery ideally must be as small as possible... Obviously, let's talk about humane possibilities here, I'm not a nanotechnology expert :smiley:

7

That sounds like around 100mA. Is everything going to be on all the time? How long will it have to run?

8

The project is to build something very similar to this:

The Parrot is powered by a single AAA battery, which makes me wonder, how did they do that...

And, umm, as long as possible? Haha. The Parrot claims to have a lifetime of 6 months. Yes, everything is ON at the same time.

9

The battery size depends on how long you want the device to run without recharging or battery replacement, and that in turn depends on the average current consumption. You need to decide how long and how often you want all those devices to run and make your decision then.

There is lots of useful information on power reduction techniques here.

10

LatvianOnJuice:
The Parrot is powered by a single AAA battery, which makes me wonder, how did they do that...

It probably isn't on most of the time, only wakes up and checks the soil and then goes back to sleep. The bluetooth only needs to be powered on when it's time to prod the person to water the plant. Everything is likely either powered off or in a deep sleep mode 99.99% of the time.

Does your soil humidity sensor really draw 35mA? That seems like way too much, even if you only need to turn it on once an hour or whatever. Take a look at this: SHT-10 Mesh-protected Weather-proof Temperature/Humidity Sensor : ID 1298 : Adafruit Industries, Unique & fun DIY electronics and kits. I think this combination draws about 1mA.

11

jboyton:
It probably isn't on most of the time, only wakes up and checks the soil and then goes back to sleep. The bluetooth only needs to be powered on when it's time to prod the person to water the plant. Everything is likely either powered off or in a deep sleep mode 99.99% of the time.

Does your soil humidity sensor really draw 35mA? That seems like way too much, even if you only need to turn it on once an hour or whatever. Take a look at this: SHT-10 Mesh-protected Weather-proof Temperature/Humidity Sensor : ID 1298 : Adafruit Industries, Unique & fun DIY electronics and kits. I think this combination draws about 1mA.

Yeah, well the deep sleep mode sounds like a perfect solution here, if I can get away with just a single AAA battery. The problem here is that the Mini requires 3.3v, plus, I'm not the best at programming the Arduino, but I feel that there are plenty of tutorials online.

Well, the Parrot does measure it all the data on a constant basis and plots it graphically, so the sensors must be on at all times(?)

Yes, the datasheet states that 35mA are drawn for optimal operation. The problem with the SHT10 (which I already looked up when selecting a sensor, is the price). The Parrot, from what I can tell, uses a very similar soil humidity sensor as the YL69, hence, the power consumption there shouldn't be a problem.

12

You could replace or bypass the regulator on your mini and use a step-up regulator like one of these: Pololu 3.3V Step-Up Voltage Regulator U1V10F3
Pololu 5V Step-Up Voltage Regulator NCP1402

I have one of them for use with a AAA battery. They work very well, they're inexpensive and they're very small. I glued mine to the battery holder.

As for everything else, read that page that jremington linked. That will get you started. It sounds like a fun project.

13

Plants need light, have a look at one of those $2 solar powered garden lights.
They are weatherproof and include a battery. Your electronics might fit inside the area above where the LED shines.

14

Yes, it definitely is a great project! I'm learning so much. Well, I decided to go with a single AAA battery and pair it up with the U1V10F5 5V boost converter (since the soil moisture sensor requires 3.5 - 5V for operation). Other than that, I sincerely hope that this all will build with very little to no complications.

Thanks for the advice, guys! I appreciate it.