I was asking awhile back about how to cut off (or save) power in a circuit with a microcontroller (Atmels at the moment) and other components. I got good answers to all of those issues, especially at how to reduce power usage on the MCU side. Now though I've come to another realization, these projects are still going to need power. A lot of the standard batteries (AA, AAA, etc.) are low voltage, generally too low voltage for the MCU, and pretty low current (Using some online calculators and giving generously low power usage still getting only a few days of power). Now some projects can easily be plugged in (window mounted weather station) while others either don't allow for it or wouldn't be desired for looks (Firefly jars, advanced LED throwies).
I am looking for suggestions on how to power some of these types of projects. Rechargeable type batteries would be nice, as having some of these things self-contained would be cool, but really I'm open to any sort of ideas, even just things to look into.
This does seem to be a good option. A lot of threads recommend this chip. The only issue I have is that the chip only comes in a SOIC package. Though I think I could manage working with them I like the option to use sockets so I can swap some of those more expensive ICs in and out. Are any of the DIP offeri ngs that would suffice or just an easy way to prototype with SOIC parts? I guess rechargable projects will get a bit expensive with the chips and probable PCB manufacturing to use them huh?
Funny enough I ordered a few of those adapters with one of my last orders. Guess they'll come in handy. I guess that also means a mouser order in the coming days for the chargers.
Edit: Also where would you get batteries and what kinds would you get? Do you get LiPo battery packs or like single cell CR123 or 18650 sizes? And how do you mount these kinds of batteries?
What you power your project with depends on how long you want it to run between charges.
I made an RFremote control that runs a month+ on a 1000mAh LiPo with the charging circuit above to recharge it from 5V.
I added power downs sleep mode, created an interrupt from button press to wake it up & send the key pressed.
Its based on 8 MHz promini, so power LED is on all the time. Could build one up standalone to use a little less power.
The battery was from gravitech.us, had to ask for it.
(Pic is missing the MAX1811 on its adapter and the Rs/Cs that go with it. )
Oh okay. So to be a bit more specific the first project I want to make is a Firefly jar as a bit of an exercise of putting together a project that is constrained by space and power and that can be left to it's own devices. I've looked at a number of tutorials and variations just to get a sense of the parts they used and techniques to make it look right. I saw a lot of them using lithium coin cells which are great because they're small and provide the necessary voltage. The only issue is that they have pretty small capacities, generally around the 200mA area. To me it seems like a really small amount to work with. I keep thinking it will run for a few days and then you'll have to replace the battery, which is a hassle and pretty wasteful. Am I just hugely over estimating the draw of a project like that?
"Am I just hugely over estimating the draw of a project like that?"
Do you mean current draw?
I don't know what goes into a Firefly jar. You can run a 8 MHz Promini on about 10mA of current with no LEDs being driven and powered from a 3.7V LiPo (4.2V when fully charged).
Alright so I've shopped around and found a number of parts for playing with.
MAX1811 chips at Mouser
Some 18650 lithium cells on EBay (a gamble)
Some low power SMT LEDs at Mouser
While I was doing that I was thinking instead of buying the 18650 cells or the ones CrossRoads reccomended, what about using cells or battery packs for cell phones/game controllers/cameras? They seem readily available at a lot of battery suppliers and even EBay and also reasonably priced.
Another piece of hardware I came across was the Max1555 lithium charger chip. On the face the benefits seem to be smaller package and half the price of the max1811. The only issue I see is that it isn't as customizable in term of output. Is the Max1555 a worthy chip?
Also I keep finding all these chips that are for charging single Li+ cells and battery packs that are made of multiple cells and wondering how do you charge them? Do the battery pack's circuits make them behave as one cell when it come to charging or are there different charging ICs for those kinds?
