Looking for some general impressions/responses here (since I don't have hard specs)
I am wondering @ a battery driven piece using Arduino and the Max 7129 chip driving a 48 LED matrix: what are my options? This is for an upcoming show and I don't have time to deal with/think about a sensor to trigger the sleep mode in the 7129 right now.
So I am wondering - how long would a 9v battery last, assuming lots of LED activity (how does one calculate something like that?). I will most likely end up tethering my piece to a power supply given the short dev time but I am curious for future iterations of this project: how much do LEDs suck up? For that matter, how long would an arduino board run off a 9v battery just by itself?
Too vague, I realize but I haven't dealt with batteries/mobile before so just trying to get an idea of the questions to ask/issues involved.
LED activity doesnt matter. Its the number of LEDs active on average.
I cant give you any estimates. Never run the Arduino off a battery before.
The biggest current draw will be the LEDs though. The chips are relatively light.
Use two 9v batteries if you have concerns.
9V batteries provide a miniscule amount fo current. Better to go for something like the MintyBoost by Ladyada at Adafruit, since:
it's based on AA's that will provide much more current
it has a very efficient power transfer ratio: (something like 90%)
With a 9V you have limited current and you will lose much of their power in heat when the 9V is converted to 5V.
See ladyada's explanation on this page, where she estimates that the mintyboost provides 2.5X more watt/hours than a single 9V: http://www.ladyada.net/make/mintyboost/process.html
With a plain 9V and a linear regulator powering 48 leds, I would guess you could get 40 minutes to one hour.
With the Mintyboost, which is just another way of saying "a well designed power supply", you could probably triple that. Using D cells instead of AA's might give you 6 hours, and best of all, you just need to buy and assemble a MintyBoost kit-- no fooling around, and the engineering has already been done by someone who knows what's what.
If space / weight are not an issue, you could use a 12V battery, like a small motorcycle battery and just regulate it down to 9V.
That should give you hours of LED activity.
hey thanks for all the comments! - just what I needed to jog my brain into thinking about the issues in powering this piece (esp. the 9v to 5v == waste/heat issue). The minty boost stuff is great too.
