SparkFun Forums

[dragonfly]

Hi, i am new to this forum and hopefully i placed my question on the right place.
Since a few years I am working with Arduinos and last week I found the minis from Sparkfun. I love its size and all connectors are easy to use.

So i just bought a few Arduino Pro Mini's (5Volt Version). In order to feed my external devices (such as breakouts like GPS, OLED and Micro SD-Card) with Power my question is:

- what Voltage output do I have on the VCC Pin if i connect a 9Volt Battery to RAW and GND
- is VCC output voltage regulated or not
- how many mAh's are available for external devices at maximum

Thank you very much for helping me with my question to this genious little Arduino Boards.

Regards,
Dragonfly

[Mee_n_Mac]

According the schematic the Pro Mini uses a Micrel MIC5205 voltage regulator. So long as the raw input is > 5.5v the output voltage (Vcc) will be 5v +/-~2%. The regulator can output a max of 150 mA, and that's for the Pro Mini and whatever else you connect to Vcc. One last thought ... I don't know how well the 5205 is heatsunk. It may be that it's thermally constrained before it hits the 150 mA. The closer the raw voltage is to 5.5v the better that situation is.
https://cdn.sparkfun.com/datasheets/Dev ... ni-v14.pdf
http://www.micrel.com/_PDF/mic5205.pdf

[dragonfly]

Thank you very much for your fast answer. Is there any kind of small battery which can run the necessary 5 to 12 Volts for the Mini (5V Version) which is as close as possible to 5Volts and does not take too much space? or do I have to buy something additional. I have some ST 7805CV Voltage Regulators laying around here but I think the heat problem would then be at the 7805CV voltage requlator side (or not)?
Datasheet for ST 7805CV is here http://pdf.datasheetcatalog.com/datashe ... s/2143.pdf
Since I wanted to build the complete circuit into a closed enclosure (http://www.conrad.ch/medias/global/ce/5 ... S_1000.jpg, I am not shure anymore if i get into trouble with this.
Thanks a lot for your help.

[Mee_n_Mac]

I don't know that a 7805 is any solution, especially as I'm not sure there is a problem. Since I have no idea what kind of current draw you might end up having, I don't know your power dissipation. This also means I can't make a good recommendation re: a battery solution. I have no idea how long it's supposed to run for.

A simple solution might be to use 4 AA (or AAA) NiMH in a battery holder and input that to Vcc via a diode. The range of voltage as the batteries run down should still make the ProMini "happy". Or perhaps you need a single cell LiPo (4.2V-3.0V) and a boost converter to make 5V from it, again to input to Vcc. Perhaps the simple solution is to use 2 LiPo cells in series and send that voltage (8.4V-6V) to normal "raw" input.

[dragonfly]

Thank you very much again Mee_n_Mac.
I will calculate first the total consumption of current for the circuit. The circuit I want to build and put into the enclosure is the following:
http://thecustomgeek.com/2012/07/15/really-smalls-gps/. In the Responses a user called "sudopeople" asks something similar (How did you wire the 3.7 Li-Po to a 5V system?), since this guy wired the ATmega328P-AU with a single cell li-po battery. But if I don't see any protection circuit for the lipo battery to not drop below (2.6 - 2.9 Volts) in order to not damage the lipo battery.

[Ross Robotics]

If you get a LiPo from Sparkfun, they all have protection circuitry.

[Mee_n_Mac]

In addition to the above, I would encourage you to code some smarts into the system. Have it monitor battery voltage and perhaps run-time and give the operator some notification of impending doom. And, as a last resort, refuse to stay powered up.