Balloons have versatile power options.
The following solutions are being developed at CUED and builds on some work over the summer of 2005 for Balloon 2.
Assuming a typical current draw of 100-200mA, several solutions are being worked on: two for robotics (12V) (where current draws can peak at around 4A with stalled motors) and one for the PDA (3.7V) being developed. For the robotics projects, the power to the balloon is provided via Chris Jones's daughterboard whereas for the PDA, the balloon is powered directly from the 3.7V
Lead Acid Batteries
Yuasa sealed lead acid batteries were selected for cost-effectiveness and availabilty: they are available in a large range of capacities, dimensions, and weights depending on particular needs. To charge, we have constructed a simple linear charger based around the UC3906 (PDF) chip from TI. The board is capable of charging the battery whilst supplying the system load; a critical design requirement for CUED.
A stripboard prototype has been developed and tested and a PCB (surface mount) version is being designed at the moment.
A custom NiMH battery pack has been constructed by All Batteries to provide 2700mAH at a nominal 12V. A switch-mode charger designed around the LTC4011 (PDF) chip from Linear is currently being developed but, due to its complexity is suffering a number of technical set-backs. Watch this space for further progress.
For the PDA, where weight is a major concern, Nokia BL-5C batteries (the type used in the very common 6230i amongst other phones) provide 900mAH at 3.7V. Two of these are being used in parallel to increase the capacity of the power pack; a Nokia desk charger or 6230i phone can be used to charge the system.
Version 2.05 has several power options:
1) 6-42V switch-mode PSU. Suitable for automotive or battery use. This is very versatile and will work happily with the nasty power you get in an automotive envionment. This option is not fitted on most of the boards shipped so far - you can tell by looking in the area in front of the Compact Flash socket on the back of the board. If you have a max629 IC, an inductor, and 4 big tantalum capacitors here then this is fitted. The 2-pin connector to the left of the CF socket (J17) is where the power goes in. +VE is the pin furthest from the big expansion connector.
2) 5V supply. If you have two max894's fitted (between the ears of the compact flash socket on the rear of the board), then you have an onboard 5V->3.3V regulator fitted and can supply the board with a single 5V regulated supply. Some 2.05 boards have this option fitted - some don't - check before powering it up! The 3.3V and 1.8V supplies are generated from this. This chip has a 500mA limit so if you fit a CF card that uses 3V then it is easy to overload this supply: if you get unreliability consider this possibility. v2.06 will be upgraded in this respect. The 5V supply is used directly for Audio, USB power and LCD bias voltage. 5V is applied to the rightmost of 3 holes in the top right of the board marked '5V'. 0V to the leftmost, marked '0V'.
3) 3.3V supply. If you only have one max894 fitted (see above 5V description), then the board needs to be supplied with a regulated 3.3V supply. The 1.8V is generated from this. The 3.3V is applied to the middle of the three holes in the top right of the board, marked '3V', and 0V to the leftmost, marked '0V'. The board can be used like this, without 5V but functions needing 5V will not work (audio, USB, LCD supply). You can supply 5V via the '5V' hole for these functions, if required, and might want to do this for efficiency reasons, because the max894 is a linear regulator and thus not the most efficient possible option. The 2.05g variant is normally supplied in this form.
NB: The 5V Supply isn't always required to power the LCD as far as I can tell. It is, however, required to power the -ve bias voltage generator, should your LCD need it. Thus, it will depend on your LCD as to whether you need 5v to run it or not. The LCD interface for the Aleph One LCDs ([BalloonLCDInfo]) will use the 5v supply for convenience with prototyping and to avoid overloading the 3.3v supply.