battery power for RPI and IR LED bank?

Question

I built a simple night vision set up using a model A RPI, pi NOIR camera, and car backup camera monitor. I made a simple infrared light by wiring 4 sets of 6 LEDs in series, so 24 total, let's see if I can do a terrible ascii style circuit diagram

____>_>_>_>_>_>__
|___>_>_>_>_>_>__|
|___>_>_>_>_>_>__|
|___>_>_>_>_>_>__|
|                |
|                \
|_____||_________|

where > is an LED, \ is a switch, and || is a 9V battery.

It works pretty well, but isn't practical because the RPI and monitor are plugged into the wall. That LED circuit is the limit of my electronics ability, so I might ask a dumb question or 10. Some poking around on the internet suggests I use something like this: http://www.suntekstore.com/goods-14002072-lm2596_dc-dc_step-down_adjustable_power_supply_module.html but I've never seen one before and don't know where the inputs or outputs are. Do you think I'd be able to run the RPI and monitor on 1 of these set to 5V and run the LED array directly on 9V? ( a series of 6 LEDs uses 9.6V, so I'm not afraid of burning them up)

Eventually I'd like to replace that manual switch with a transistor and control it from the GPIO pins, but I don't know what pin would be best, never used them before.

Also, any suggestions on a battery big enough to do this?

EDIT: Here are the LEDs I used: http://www.adafruit.com/products/387

They are 1.6 forward voltage and 100mA continuous current. I would have done 5 groups of 5, but one didn't work so I went with 4 groups of 6. 6 in a row seemed easier because 6 x 1.6 is 9.6V, so I figured the LEDs would eat up all the voltage from the 9V battery and I wouldn't need a resistor to take care of the rest. I'm not 100% sure what I'd use this for yet. If I can run the monitor, RPI, and LEDs off battery for a decent amount of time, I could strap it to a helmet and make a poor man's night vision goggles. I could also remove the monitor and set it up as a night time camera for watching animals outdoors. If I can't make a battery practical, could just use it as a surveillance camera in my house.

A rechargeable battery would be nice, and I've seen a few people using those USB battery packs for recharging cell phones, but but I've only seen them at 5 volts.

Answer 1

Your night vision project actually sounds really cool! I like the idea a lot. Talk about bring the future into the palm of your hands.

I think your logic on the LEDs and voltage checks out. Usually anything under driven is safe. The reason for resistors with LEDs is sort of a safety thing, reducing the voltage and providing current limiting so that the LEDs won't blow instantly with over-voltage (over driven LEDs sometimes... just explode, rather than stop working nicely). I think under-volting cancels out the need this case.

I think the regulator you selected would work, but you'd probably need two. One to drive the LEDs and one to drive the Pi. I'm not entirely certain about driving the Pi with it though. There's a tendency for cheap electronics to introduce jitter. That is to say, slight fluctuations in the power that might cause unexpected consequences in the Pi. I definitely would not connect it to the GPIO header as that by-passes all the current protection in the Pi, particularly the self-resetting fuse.

What might be a really good fit for you might be the MoPi board. It's a little bit more expensive, but takes care of all the regulation, etc., when using battery power. For example, it'll inform the Pi when the voltage gets low and trigger a nice shut-down. It should run the Pi for around 10 hours on 8 rechargeable AAs. There's probably plenty to spare there for powering your LEDs and the rest of the equipment for a decent bit. Or use a large sealed lead-acid battery for longer battery life.

Answer 2

I use a Halo Rechargeable, which can deliver up to 5v @1500mA. The newer one can deliver up t- 3000mA. Do a search on ebay, amazon etc for a portable phone charger. My halo works great and powers by Pi with a PiTFT display.