Hi All,
Over the past weeks I probably read all the topics on this forum about LiPo/LIon batteries on this forum, but still not fully sure about the correct safe design for my project.
OBJECTIVE: Have an Arduino Uno (later maybe just the 328 chip with the crystal) with a few connected auxiliary sensors requiring 5V. I want a nice compact package with the ease of recharging like a phone or a gopro.
Having learnt about the dangers of not operating properly LiPo batteries, I want to double check with you guys what is the best solution to achieve my goal. I now have a 1000 mAh LiPo cell which I only tested for good storage voltage but not tried to power anything as I have not got yet the recharging hardware. According to the advertisement specs, the protective built-in PCBs charging module, should include over charging, over discharging, over current and short circuit circuit. My guess however would be that especially the over discharging protection is somewhere at 2.5V, which is ok as a last safety measure, but not to keep the battery alive. Therefore I need further configurable protection.
Because it is a 3.7 V, and I need 5V, I need also a step up converter. Correct me if I am wrong, but I also see it as a good way of having a relatively stable supply voltage, compared to the one of the battery which will drop from let's say an initial 4.2V down to 3.3-3.5V?
Finally, because I want to charge this thing with a simple usn charger as with a normal phone, I need a charging circuit, taking in 5V and following the correct charging cycle required by these batteries.
I have found and bought these two 3-in-1 boards which are supposed to provide what I need.
On the paper it all seems good, but I expect to do some testing to see that they behave as expected. If any of you have some experience with these, I would really appreciate to have some feedback.
Assuming that this 3-in-1 board with the battery I have make sense to you guys, and achieves what I am looking for, this is still not enough. In fact, I was thinking to hook the 3.7 V cell also to one of the Analog inputs, in order to check in software the state of the battery, and set the low threshold below which not to enable the device to work at all. I am assuming that the step up circuit would provide the same 5V at any healthy state of the battery, and with this as a reference, I hope to have a good reference for the 328 to check the actual voltage of the cell.
Finally, how do I auto-kill the device once the low voltage is detected? I have learned a bit about latching ciruits, and was thinking about something like this...
This circuit requires the GPIO pin to be set to high at the beginning of the code. And because of the booting time, if the user releases the button earlier, the device will never start. I do not see it necessarily as a bad thing. A sort of an accidental button press protection. But my main question is where should I be fitting this circuit? Initially I though that it would be sitting between my 3-in-1 board, exactly between the 328 and the stepped up voltage. But I am not sure what is the quiescent power consumption of this 3-in-1 board once I kill the actual circuit. The idea would be to cut to zero the power consumption once the low voltage state is detected. The device should just start up, do the battery check, and auto-kill.
The other point I thought of fitting this circuit is between the 3.7 cell and the 3-in-1 board. The problem is what happens then during the charging? I know that mosfets allow current flow only from the source to the drain. So if I put the protective break circuit just after the battery, I won't be able to charge it... Perhaps I can have another parallel mosfet in the opposite direction, which would be turned on by the usb voltage?
Thank you very much for the support! And I apologise if I missed something or got something wrong. I am a mechanical engineer, and learning about electronics as a hobby. I hope this topic will become the definitive answer to all the beginners like me trying to build a stand alone Arduino running on a LiPo battery.
