I've tried searching but I think I'm either being dumb or blind.
I have a project that is currently using a Nano and nRF24 module as a wireless control handset.
The end goal of this is to have it running off a battery so it is completely wireless.
In a perfect world what I would want is to have a built in rechargeable battery that I can charge in situ using a USB cable. As this is a handheld unit it needs to be as small and light as possible.
I'm basically after some advise on the best way to do this. I'm also no apposed to using a different board if there is a more suitable option as long as it has enough IO pins, I'm using 18 pins on the Nano ATM.
A lot of IOT boards have a built in battery interface. Mostly ESP based.
Well, first thing is that while the Nano is clearly far more practical than the UNO, it still carries a USB interface chip that is not wanted when not connected to a PC via USB, takes up space and is wasting battery current.
So a Pro Mini is more appropriate. And you can get a Pro Mini with an 8 MHz crystal that runs on 3.3 V.
Now if the NRF module will tolerate the 4.2 V charge voltage of a LiPo (I am not familiar with its exact specification), you could run everything directly from that and include a charge module with a USB socket.
Unfortunately the nRF24 hax a max voltage of 3.6.
On another forum I have been recommended the Adafruit Powerboost.
Having a look there is a 500ma and 1000ma version, I would have to do some testing to be sure I don't exceed these.
If I were to use this would my best bet be to have a 3.3v regulator on my mainboard and swap out the nano with something that runs on 3.3v or is there a 'better' way?
If you have no 5V requirements then the best solution would be to use a buck regulator to 3.3V instead.
Boosting the voltage from a 3.7V battery up to 5V and then regulating it down to 3.3V again is plain crazy.
Choose all your components to use the same voltage if possible. The NRF modules are all 3.3V so choose an Arduino that's also 3.3V. A possible alternative to the 3.3V Pro Mini is a 3.3V Pro Micro.
When powering 3.3V devices with a 3.7V battery, it's best to use a low drop-out regulator such as mcp1700 to maximise battery life, but absolutely do investigate the max current your device will draw first. The mcp1700 can supply 250mA max.
For the battery, there are a large number of different size li-po packs available, so you can choose among the sizes that will fit your enclosure and provide maximum capacity. Many of these li-po packs have built-in circuits to prevent over-discharge, which is an important safety feature. Charger modules with a mini or micro usb socket are commonly available.
As an alternative suggestion, It would be worth taking a look at the Adafruit ESP32-s2 feather this not only has a dedicated JST 2-PH Lipo battery connector it also encompasses a battery charger & a LiPoly / LiIon Fuel Gauge and Battery Monitor.
You would then also be able to make use of ESP-NOW instead of using the nRF24 modules which can be a bit temperamental!
Thanks for the advice.
I've ordered a Feather as well as a basic ESP32 Dev board and will have a play with ESP-NOW.
Unfortunately my current base station used a 5V CAN controller and transceiver so the next thing I need to work out is what CAN transceiver to use.
Could simply use 3.3v devices with a diode on the 3.7v supply.
Voltage would be down a bit but could be tolerated.
Adafruit's Feather M0 radio modules run from LiPo batteries, and have a built in USB charger. All in one solution.
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