Is it not possible to do an analogRead(A14) for the 1.1V reference?
I haven't tried that, but I doubt it. I suspect the code that implements analogRead() for the 328P would consider A14 to be an invalid pin number, or an undefined variable, and error out.
But there may be some library that provides for measuring battery voltage this way. I just haven't found one.
You are right, A14 is not defined for Uno&Co.
Should we ask for a firmware update?
The problem seems to be that Ann is defined only for physical pins, not for internal multiplexer channels.
I eventually was able to test it. It works perfect. I set a divider to lower the voltage and the measure is stable and consistent with "tester" readings.
I have a further question. As the analogReference(INTERNAL) applies to ALL analog pins, does it influence the SDA SCL (A5 A5) to which I connect the I2C display? If yes is there a workaround or they just are not compatible?
Flavio
No, the internal reference does not apply to the pins but only to the ADC. I2C operation is not affected by the ADC reference.
1 Like
As you are so competent, I wonder if I can add a question without breaking any forum rules...
Now that I have the 3.7 Li Ion battery attached to the PRO MINI and have understood how to measure the voltage (even from time to time to avoid extra consumption) ... how do I charge the battery? Do I have to detach it phisically from the Arduino or is it possible to just let the (5V) flow in the circuit?
Thanks in advance, if you can.
Flavio
I don't think so but I have no idea of any details.
For sure not just by applying 5v to the circuit ! LiPo batteries are difficult to handle and require very specific charging methods.
If charged incorrectly they may explode, so take very good care.
There are USB charging units available online, and they are mostly based on the TP4056 IC. You can modify the charging current by changing the 'prog' resistor, to set it to a current no higher then 2C But 1C is the safest.
Check this article.
In most cases, the chargers do not allow for load sharing and so the battery should be disconnected. (there are ways around this) . Using a circuit that does not allow for load sharing means that if you do, the charging circuit may keep charging when the battery is full, which may cause it to explode.
Also you should protect your battery from over-discharge, which will ruin it for sure.
this tutorial shows the schematic of a charger with protection and booster circuit (which you don't actually need) But to built that, you will need tweezers to hold the parts. Modifying a circuit to allow for load sharing can be done as easily as by adding 2 diodes, but let me stress again : Lipo batteries are dangerous and should be handled with care !
1 Like
Thanks!!! I do have a big LiPo charger for a model airplane that takes care of all the charge/discharge process - although something like a "watch" it will not be very comfortable.
I thought of using one of the chargers that can be connected to the USB. Will read the article and decide. You confirm what I thought... that given how dangerous they are, you better not charge them in place. Also ... given the very contained target dimensions of the whole thing to add components to keep it inside is... slippery.
Difficult to consider another type of battery. Perhaps a button not rechargeable.
Flavio
Thanks, anyway.
I know if you have a single 18650 battery there are many charger IC boards on ebay. They control the current and voltage so to not damage the battery. Assuming your Pro Mini is not using a lot of power I thing you will be able to charge the battery and run the Pro Mini simultaneously.
The chargers stop at 4.2 volts, well within the capability of the Pro Mini.
That's good. Does it take the size of the battery into account.
One of the links describes how to built one. If you add 2 diodes. 1 from USB 5v+ to VCC of the object to be powered, and 1 from Bat + to the object to be powered, booth with the Cathode towards the object, you can sort of load share. 5v+ is always going to be more than the battery voltage (also during charge)
This is the system i use for the backup battery of my alarm-clock.
The charger can be built fairly small, i build units with 100mA LiPo and add these to clip-on guitar tuners
Well yeah, button cells are fairly cheap, and really small, but they don't come rechargeable, and they are very difficult to recycle, so bad for the environment.
1 Like
Be sure the "BIG" charger uses a current rating that is appropriate for you (I assume) smaller cell.
I will test all of it! Thanks. The battery is 3.7V (max 4.2) and the ProMini is the 3.3V kind. My "big" charger is very sophisticated so it should take care of everything but surely it is better to have a small compact one.
Flavio
You might want to look at a board like this.
1 Like
Cheap and... mean!! Tks!
F
You can change the 'prog' resistor (1.2K marked 122) without much issue to match the charging current
see the table At 1.2K it is set at it's 1A maximum, which would be 1C for a 1000mAH battery.
You have opened another issue, I looked... my battery is 250mAh (watch size) and the charge current is only 125mAh (your table arrives at 130mAh which I suppose is a fine match).
F
That is only .5C You could also go for the 5K resistor which will charge the battery in an hour. As said it is not hard to remove the SMT resistor and you can replace it with a THT one if that's all you have. The important part with LiPo's is that the charging current should be constant.
1 Like
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.