how does that relate to the 200maH that the 9V block has?
I am considering using several batteries in parallel
If you're "in the field", then connect it via a cow. The louder it moos, the more current you are drawing.I would probably use a lithium based power source for that kind of life time.It's hard to advise without knowing actual current draw.
I thought 20 LED would be easy to run for a day
I am "in the field" and the little pocketmeter i brought can't measure A
maybe use an ldo regulator to keep the battery voltage as close to 5v as you can
Quote from: fubbi on May 28, 2012, 05:55 pmI am "in the field" and the little pocketmeter i brought can't measure A I would -love- to see a picture of this meter;
With 9V, you can connect LEDs in series.4 LEDs in series will drop approximately 6-8 Volts (depending on exactly which LEDs you're using). Add a resistor to limit it to 20ma. (If your LEDs use 6.8 V, the remainder is 2.2V that the resistor has to drop. 2.2V/0.02A = 110 ohms.)Make 5 strings like this for a total of 20 LEDs.Total current draw is 5 *20ma = 100ma.