What will I need?
I think I finally decided on what to use for powering the helmet devices. My February article didn’t give to much technical detail about what would be used. It was more a to do list for what to spec out. My March article was more toward the auxiliary power supply to USB devices. Nothing so far specific to the helmet nor detailed enough to be of any use.
The figure that I’ve estimated for all of the devices is 800mA. The Arduino Micro is rated for a max of 40mA per I/O. Meanwhile, the Mobius camera can use around 550mA. This leaves me with 250mA for the sensors, which should be plenty.
Adafruit has the parts all ready for this project…
The Lithium Ion Battery Pack – 3.7V 6600mAh they sell would be able to power the hardware just over 8 hours. This is a high use estimate based on peak current draw throughout the operation of the hardware. I’m thinking that I’ll get a longer operating time.
The next piece of hardware will be the PowerBoost 500 Charger – Rechargeable 5V Lipo USB Boost @ 500mA+. This does quite a few functions. First, it will take the 3.7 volt input from the battery and boost the voltage to a regulated 5 volt level. Next, it will charge the battery pack when an external power source is applied to the USB port. It can charge at a 5oomAh rate. This means it can take over 13 hours to recharge from dead. Also, it has multiple connection points to hook up devices and interfaces. As far as load is concerned, it can handle an output of 1000mA. This should handle the current draw from all the hardware without issue. Finally, it can be powered off with a switch.
What about tracking the power use too?
Adafruit also offers a USB Power Gauge Mini-Kit which can send the volt, amp, and watt reading in a serial stream. This will be helpful in the build and overall use of the sensor helmet. The readings are precise, there is some drift due to thermal factors. The Adafruit product page has more details. This device will be separate from the rest of the power equipment and embedded inside the helmet.
How is it going to fit?
The battery pack and power boost will be housed together behind and outside of the helmet. I’ll leave a way for a charging cable to connect to the USB port of the charger. I would also like to have a way to view the charger LEDs. I might use a smoked covering so it will be visible when lit, but dark enough to block the circuitry inside. The power cables will run inside the helmet to a detachable connector, then on to all of the hardware. I’ll use Velcro to attach the housing to the helmet. The housing will be weather proof so it can be used in all weather. Tap Plastics will most likely be utilized for the housing fabrication.