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I am putting together a PiPhone but with slight mod to the power.

Is it possible to use powerboost 1000 charger to achieve the following?

  • power up rpi + pitft and the sim module,
  • recharge battery and/or power the devices directly when battery is low,
  • terminate power output to all devices via the switch on powerboost charger

The rest of the wiring is known, except how to wire powerboost charger to the sim module.

The sim module receives power and charge its battery via the 5v micro usb port. The jst on the powerboost charger receives 3.7v for the battery. What is the simplest way to allow the sim module to receive stable 5v power output from the powerboost jst?

Wiring reference: adafruit piPhone

My powerboost differs from this wiring link. I need to implement a switch on the power booster. Also I want to connect vio to the TFT 3v instead of to FONA Bat+ so I could do a data failover. prelim wiring attempt

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Use the powerboost to power the pi only. Do not power the SIM and it's battery from the raspberry pi. (I'll explain how to wire it first, then I'll explain why...)

First-

  • wire the powerboost so that it's got a micro-USB on the 5v and Gnd (this will plug into and power the pi)
  • connect the +Bat and Gnd of the power boost to the +Bat and Gnd lines of the FONA
  • take your lipo (2500mAh-5000mAh) and plug that into the FONA JST-ph

You can plug your charger into either the powerboost or the FONA to recharge the battery(but not both at the same time).

The why-

  • there is a 'resettable' fuse between the USB and the 5V pin on the pi so it's not safe to power it from pin 2 or 4 on the GPIO
  • The fuse also makes it inadvisable to power the FONA from the pi, the FONA can draw between 20-500mA depending on what it's doing
  • You don't want to put the FONA after the Powerboost as it (and the pi) can draw more than the Powerboost can supply (during a voice call or GPRS data especially. see p. 60 of this- http://www.adafruit.com/datasheets/sim800h_hardware_design_v1.00.pdf)
  • The FONA powers itself directly from the Lipo battery anyway. The only thing it uses 5V for is to charge the battery. So if you use the battery to power it's own charger you are just generating heat ;-P

So the most reliable solution is use the FONA battery to power both devices. The powerboost only runs the pi which leaves you more power to do stuff with and there's less chance of popping the 'resettable' fuse, which takes hours to days to reset.

BTW - powering an Arduino as I describe I'm using around 100mAh. Most of that is the SIM800)

  • What I've described is identical to the link you posted from Adafruit. One battery powers both the powerboost and the FONA. (hence the Bat+ on the FONA connecting to the JST battery connector on the powerboost.) This is the most efficient way to do things as the FONA runs on the raw battery but the pi needs 5V. Remember though that between the FONA and the pi your battery usage could be 1000mA/h. So to plan your battery size accordingly. – alphacharlie Jul 10 '15 at 20:54
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    Vio on the FONA is ONLY for the logic level. It should always be connected to the 3.3V out for the pi(because the pi uses 3.3V logic). The FONA does NOT power itself through that pin. You can still totally use the EN pin on the powerboost to switch it on and off. But you will still connect the Bat on the FONA to the Bat pin of the Powerboost.(and the Gnd to the Gnd too), the FONA will not be turned off and on with your switch. You can turn it off (or on) from the PI via GPIO by pulsing a low signal to the Key pin for 2 seconds. – alphacharlie Jul 11 '15 at 3:00
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    Note - The 'homemade cell phone' project you linked to on Adafruit does show the Vio connected to the bat pin. This will probably work for the most part. But it's still not a great idea because you are telling the FONA that a '1' is a 3.7->4.2V signal then actually giving it a 3.3V signal. So there is a possibility that it will sometimes miss '1's. (I hope that makes sense.) – alphacharlie Jul 11 '15 at 3:26
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    That is exactly right. You can totally connect two batteries that way, one to the FONA and one to the Powerboost. (each to the JST-PH). That connects them in parallel.To avoid balance issues, you should use two of the exact same battery if you go that route. – alphacharlie Jul 11 '15 at 5:58
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    Thank you. This gives me a good start, until this noob gets deeper into it. – Sean Lee Jul 11 '15 at 6:07
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I would say that it should work.

Use the Powerboost 1000 battery charger to power the RPi and all things connected to the RPi. Notice that it just delivers 1000 mA and that all connected devices must not use more than 5 W.

The screen could be powered from the RPi 5 Voltage pin out (if that is within the specs for RPi), from the RPi 3.3 Voltage pin out (also see the RPi specs) or directly from the Powerboost 1000 Charger in parallel with the RPi.

The GSM SIM Module could be wired to a RPi and getting its power from the RPi:s 3.3 Voltage output, as per this link from Ada Fruit.

No, I have not tried this, but see no reasons why it shouldn't work, except that the marginals could be a bit slim with 1.0 A max output from the Powerbooster.

  • You meant to refer to the pin #2 or #5 on Rpi to connect to Powerboost? As for the GSM, if I wired it to RPI, that would mean I need 2 batteries. One attached to GSM, the other on powerboost. Anyway to just use 1 battery? Speaking of the current load, Rpi could max to 400mAh, GSM probably requires 50mAh. What kind of marginal you'd recommend as safe? – Sean Lee Jun 17 '15 at 15:42
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    Anders - The Pi is not powering the FONA in your link. The SIM800 takes it's power from the Bat+ pin, Vio is for logic level shifiting only. Specs from the datasheet say the SIM800 needs 3.4-4.4V on Bat+ with a recommended voltage of 4VDC for the FONA – alphacharlie Jul 10 '15 at 21:13

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