FONA + PowerBoost + Arduino

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lectroidmarc
 
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FONA + PowerBoost + Arduino

Post by lectroidmarc »

Hi all,

I was wondering if this will work: An Arduino + FONA + PowerBoost 500 Basic. Using the 5v output from the PowerBoost to power the Arduino while at the same time connecting the Bat pin on the PowerBoost to the Bat on the FONA to power that directly off the LiPo.

Seems like that should work, yes? 5v for the Arduino, and ~3.7v for the FONA.

Bonus question, could the LiPo be charged via the FONA this way? Also seems like that would work, but before I make things smoke, I thought I'd ask.

Thanks

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adafruit_support_mike
 
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Re: FONA + PowerBoost + Arduino

Post by adafruit_support_mike »

It should work, with a couple of minor warnings:

First, you'll want a LiPo that can deliver enough current. The FONA's radio can draw up to 2A at times, and as a rule of thumb, most LiPo cells can deliver current at a rate that will discharge them in 1 hour without any dips in the voltage or risk of overheating. The FONA's high-current load times are short enough and far enough apart that there's no risk of overheating, but they could cause power spikes that would cause problems for an Arduino.

We suggest using at least a 500mAh LiPo with the FONA, so I'd suggest going up to at least 1200mAh for the FONA and a PowerBoost.

Second, charging is kind of a yes/no situation. The FONA uses an MCP73831 LiPo charge controller, which is the same as the one we use in the Micro Lipo charger: https://www.adafruit.com/products/1304

The MCP73831 is relatively simple as LiPo chargers go. It charges the battery up to about 4.2v, then waits for the voltage to fall to 3.2v before starting the next charge cycle. It doesn't do any load management, and it has built-in safety systems that will abort the charging cycle if the cell voltage doesn't rise to a certain level in a certain amount of time. When the charger is active, it will provide power to both the LiPo and anything connected to it. If the combined load is enough to keep the cell from charging at the expected rate, the MCP73831 will shut everything down.

The FONA's charger is set to provide 500mA of charging current, and I honestly have no idea what effect a PowerBoost would have on the charging cycle. It depends heavily on the amount of power the Arduino wants.

For that part, the best I can say is, "try it and see". An aborted charging cycle won't damage anything, but you may have to disconnect and reconnect the battery to make the MCP73831 happy again.

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lectroidmarc
 
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Re: FONA + PowerBoost + Arduino

Post by lectroidmarc »

Ah well, one 1200mAh LiPo would be better than two 500mAh ones, so that's a plus :).

Really the charging question boils down to if I want to use the PowerBoost Basic (and charge via the FONA) or the PowerBoost Charger. And really, that's more a question of space available :). It sounds like either would work, but using the PowerBoost Charger would be the preferable solution.

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adafruit_support_mike
 
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Re: FONA + PowerBoost + Arduino

Post by adafruit_support_mike »

Yeah, the PowerBoost Charger would be a better choice. That's specifically designed to charge the LiPo while the circuit is running.

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snoller
 
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Re: FONA + PowerBoost + Arduino

Post by snoller »

Guys, is it possible to reduce the load-current that Fona is trying to apply with a resistor or by any other means?

Background: we want to use Fona together with a Raspberry. The Rpi can provide something like 300mA on the 5v Pin if no USB-Devices are in use. Fona does not work without a battery and it has to be charged. Ideally the load current could be reduced to say 250mA, does that make any sense?

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adafruit_support_mike
 
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Re: FONA + PowerBoost + Arduino

Post by adafruit_support_mike »

That's pretty much like trying to go 500 miles on 10 gallons of gas in a car that gets 30mpg. There's no way to arrange the numbers that gives the result you want.

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snoller
 
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Re: FONA + PowerBoost + Arduino

Post by snoller »

Sorry, but i am not getting it. The Rpi has 300mA available. Fona wants to charge with 500mA. Why cant i reduce the load current by placing a resistor for instance?
The micro-charger from your shop does charge the same battery with 100mA for instance, so why shouldn't the RPi? http://www.exp-tech.de/adafruit-micro-l ... charger-v1

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adafruit_support_mike
 
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Re: FONA + PowerBoost + Arduino

Post by adafruit_support_mike »

It's possible to change the amount of current the MCP73831 LiPo charger delivers, but that doesn't change the FONA's current consumption.

The FONA uses about 25mA at idle, but while making a call the consumption rises above 200mA with spikes up to 2A. On its own, even a 500mA charger can't keep the FONA running while making a call. If you reduce the charging current to 300mA, most or all of that will go to the radio while the FONA is making a call, and the radio will continue to pull 2A pulses from the LiPo. There's a good chance that the LiPo will continue to lose charge, even when connected to a 300mA external source.

Running headphones or external speakers will add an additional current load.

It's possible to keep a FONA running under those conditions, but only if you limit the length and frequency of calls so the LiPo can charge faster than it discharges.

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