Minty boost along with a blink program.

Ideas and questions about MintyBoost kits

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khaledm
 
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Minty boost along with a blink program.

Post by khaledm »

Hi all,

So here goes my first post:

I have this idea to run a GPS Dongle over an extended period of time (about 7 days) without interruption. I've enlisted a minty boost hooked up to 3X 1.5 Energizer E95 (they claim to hold a whopping 20,000 mAh!). The problem is if I don't keep an eye on the GPS device, the unit would stop drawing power once it was fully charged and then run down to dead. This, in effect, makes it only of use for about 12 hours. My Idea then was to add a small circuit using an ATtiny 85 with a blink program (i.e. turn on for 3 hours of charging, turn off for 6 hours of use, repeat until the batteries are dead).

Here's where the trouble is: with the added circuit (really just an ATtiny chip and a USB female connector on a small bit of PCB) the dongle won't even charge. I'm still new to electronics, and only bothered running the positive and ground through the Tiny. I'm wondering if I need to run the two center terminals of the Minty Boost over the Tiny and straight through to the female USB. Or, maybe I've not thought this through at all. I'd appreciate some guidance.

Some of my reasons for going this route of using alkaline batteries through a Minty Boost, as extra long life energy system, are:
-the Minty will utilize more of the available power of batteries, running them down to nearly dead while maintaining the needed 5 volts
-Sourcing out alternatives for a power supply, I found that these D cells are the best deal for the buck.

Please point out any errors in my reasoning and possible ways to make this project work.

Thanks

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adafruit_support_bill
 
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Re: Minty boost along with a blink program.

Post by adafruit_support_bill »

A circuit diagram would be helpful. It sounds like you are trying to switch the charging current with the ATTiny directly. The GPIO pins can only handle a few milliamps. You would need a power transistor of some kind to handle the full charging current..

khaledm
 
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Re: Minty boost along with a blink program.

Post by khaledm »

Hi,

I can't think of a way to send you a diagram. You're right, from your assessment, as to how I tried to approach this.

A verbal description of the circuit would consist of something like this: the Minty is assembled as instructions except that the female USB connector is left off. Running from the open positive and ground connections of the Minty are connections to Pin 8 (positive) and Pin 4 (ground) of the Tiny. Using a split from ground of the Minty and the positive from Pin 2 of the Tiny the 1 and 4 pin of the USB are wired.

Could you please tell me how to best hook it up so that it runs?

khaledm
 
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Re: Minty boost along with a blink program.

Post by khaledm »

Hopefully this helps with the visual.
Attachments
Minty Tiny schematic.png
Minty Tiny schematic.png (6.69 KiB) Viewed 2058 times

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adafruit_support_bill
 
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Re: Minty boost along with a blink program.

Post by adafruit_support_bill »

Instead of feeding pin 8 directly to the USB, you would connect it to an N-channel power MOSFET that would switch the current. http://www.adafruit.com/products/355

The Source pin of the MOSFET would connect to GND
The Drain pin would connect to the negative terminal of the USB connector.
Pin 8 would connect to the GATE of the MOSFET.
The Positive terminal of the USB would connect to the positive terminal of your MintyBoost output.

khaledm
 
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Re: Minty boost along with a blink program.

Post by khaledm »

Thanks for the expertise and your time. I'll read up on transistors to familiarize myself with the concept.

khaledm
 
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Re: Minty boost along with a blink program.

Post by khaledm »

http://tinypic.com/r/o10tmt/8 (Link to photo)

I tried the configuration you described. I doesn't seem to work. The output at the minty boost is 4.93 V, yet at the USB it's -.73 V.
Any help would be appreciated.

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adafruit_support_bill
 
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Re: Minty boost along with a blink program.

Post by adafruit_support_bill »

The chip is not powered. So there is no signal going to the gate of the MOSFET.

khaledm
 
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Re: Minty boost along with a blink program.

Post by khaledm »

Does the chip need both positive and ground or is + good enough?

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adafruit_support_bill
 
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Re: Minty boost along with a blink program.

Post by adafruit_support_bill »

It needs both VCC and GND to run. Have you already programmed it with your blink program?

khaledm
 
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Re: Minty boost along with a blink program.

Post by khaledm »

The chip is already programmed. Pin 2 (+ out), Pin 4 (GND), Pin 8 (+ in).

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adafruit_support_bill
 
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Re: Minty boost along with a blink program.

Post by adafruit_support_bill »

Have you tested your circuit? If you connect an LED to the output of your processor, does the LED blink as expected?

khaledm
 
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Re: Minty boost along with a blink program.

Post by khaledm »

The circuit was tested after the Blink program was installed on the AT Tiny. A simple sketch is all I need to complete this project. Something that outlines how the MOSFET is incorporated to make the Dongle charge.

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adafruit_support_bill
 
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Re: Minty boost along with a blink program.

Post by adafruit_support_bill »

The Source pin of the MOSFET would connect to GND
The Drain pin would connect to the negative terminal of the USB connector.
Pin 8 would connect to the GATE of the MOSFET.
The Positive terminal of the USB would connect to the positive terminal of your MintyBoost output.

The MOSFET wiring in the photo posted earlier was correct. You just need to program and power the ATTiny to drive it.

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