this is my first time in this forum and actually the first time I'm buying Arduino stuff. I worked on electronics in the past including different types of SBC's. Now, I would like to build me something for the garden, where I would have the following requirements:
1.) Have a microcontroller with as little power consumption as possible
2.) Connect an IMU (preferably BMI088) to it and read the data in 30-40 Hz
3.) Connect a Bluetooth Low Energy sensor and broadcast the data from the IMU
4.) Power the whole thing using a 4xAA battery pack and read the battery level every 10 minutes or so using the microcontroller.
5.) Set the BLE sensor to sleep, if some criteria is met (for example, the device is sitting still for 30 minutes.
Can you suggest me something to start from, otherwise I'm a bit overwhelmed by the variety of sensors that are available and which ones are the best for this project.
I believe the Nano 33 BLE is the best option, since it has a 9 axis IMU and the RP2040 most likely consumes more power. I have troubles extracting the power consumption from the data sheets, maybe someone can help me here.
Then only the battery is missing. I'm thinking about a 4 or 6 pack of AA batteries. I thought of something like this: Battery Holder
I really don't know if I can connect it through the pins, or what I should look out for here. I want the batteries to be rechargeable - I thought about 4-6 x Eneloop Pro NiMh: Eneloop Pro
Hi, thanks for the suggestion. I saw this article and what I got from it is, that I would go for the 3.3V Vin and use 3x 1.2V AA NiMh Batteries. I wasn't sure if 3.6 is too much and would damage the device. So, I think the 33 BLE board is pretty much the best choice for me and I would like to ask for your expertise, if the 3 battery option is valid.
Also, I never used Arduino. I'm sure I need a devkit or something to flash/program my code onto it. Can you suggest me, what I need for that? I will also read more on that topic, but I don't want to order something and when I get it, realize that something is missing. I hope I can start soon, since I'm very excited already.
EDIT: btw.: Does anyone know, what the power consumption would be, if I send 1 kB/s per bluetooth continuously?
The 1.2V figure is nominal. NiMH battery voltage ranges from about 1.5V to 0.9 V during the charge/discharge cycle, and using 3 of them would destroy devices with a narrower operational voltage range.
Many people would use a 4X NiMH supply and a low dropout 3.3V regulator instead.
Study the Arduino page for that board. It has lots of useful information.
Thanks, I will read that for sure tonight. I just see currently, that the power consumption and the battery charge might not be enough for my use case.
I saw, that "doing nothing" on that board would result in 7.6 mA and considering, that I would need to broadcast 30 Hz IMU data from this device via BLE, I estimate the consumption to be around 50mA (but I have no idea really, how much it would be). Considering the 4 serial 1.2V batteries with ~2500mAH, I would roughly survive 2 days. It would be very helpfull to get a good estimation on the power consumption using this setup, so I can figure out, if this board is useable for my project or not.
I would try to use 2x (3x 1.2V) battery packs in parallel in order to double the lifetime, and implement a sleep mode, but my goal is 1 week at least and I believe, that will be hard to achieve.
50mA sounds a bit high to me. BLE uses ~8 mA when transmitting. You can turn off any sensors you are not using, but you probably won't get much below 15-20 mA.
Since this is your first Arduino project, consider it a learning experience. There is a lot to learn, one point being that Arduino is not designed for low power operation.
Thanks for all the information. I think 20 mA sounds good for now. It is basically a prototype to get a feeling of what is important and what is possible. If I can achieve 5-10 mA with another solution, the result would be perfect already. I will go with the mentioned hardware. Maybe a serial 3 AA Battery pack with 1.2V*3 = 3.6V input and 2550 mAh. Later maybe set two of those battery packs in parallel, but my last question really is: Does that 3.6V work on the 3.3V input, or should I also put a voltage reducer in between? Is there some schematic of those reducers, from that I can see how I need to connect it in my board?
No. As I said earlier, the battery voltage is NOT "3.6V".
The 1.2V figure is nominal. NiMH battery voltage ranges from about 1.5V to 0.9 V during the charge/discharge cycle, and using 3 of them would destroy devices with a narrower operational voltage range.