Power issues: 5V MAX7219 vs. 3V nRF24AP2

Now, a problem with the system is that the display controller (MAX7219 must run on ~5V) and the ANT+ module (nRF24AP2) is at ~3V.

To over come the differences a level converter was employed (http://www.freetronics.com/products/logic-level-converter-module).

Worked like a charm.

Now, we still have a problem in that our LiPo batteries aren't going to give 5V (even 4.2V at full charge wasn't enough to get the display updating properly).

Prototype one (without ANT+) used a boost converter to get to 5V from a single battery however the battery ran out after about 3.5 hours on the road.

As we need more power capacity and increased voltage I just added another identical battery in series and a 5V regulator (https://www.sparkfun.com/products/107).

This gives me a 5V source for the display subsystem and the Arduino Pro Mini 3v3 has its own 3V regulator.

The level converter is then put between the 3V Arduino SPI signals and the 5V display.

What would we need?

What would it take to make this display?

• A micro-controller
• A power source
• An ANT+ module
• A display 
• An ANT+ source of distance information (Garmin Forerunner 410 Foot-pod)

MCU
I have quite few Arduino boards lying around, so that seemed to be the easy choice on the processor. I ended up using a Tinyduino (Tinyduino) and an Arduino Pro Mini (link) in my two separate iterations.

 Power
I also have some LiPo batteries around from other projects. Lightweight and powerful (link).

A display
7-segment displays are cool in my opinion and so that was the display I decided would make most sense (in spite of the difficulty in getting some letters represented). These seemed to be good and cheap options based on the MAX7219 (http://dx.com/p/8-segment-led-display-board-module-for-arduino-147814) and cheaper than I could get the main chip for myself.

ANT+
An ANT+ module for talking to the Garmin. This would need to be purchased. The sparkfun modules (link) seemed good - however they weren't available anywhere. I ended up buying from Goodluckbuy.com in China (http://www.goodluckbuy.com/nrf24ap2-wireless-module-zigbee-module.html)

Source
I have a Garmin Forerunner 410, Heart Rate Monitor and Foot-pod.