Does anyone know the minimum voltage & amperage requirements for the "ATmega328"? I'm asking about the chip itself, not the whole arduino.
From the spec sheet:
• Power Consumption at 1MHz, 1.8V, 25°C – Active Mode: 0.2mA – Power-down Mode: 0.1?A – Power-save Mode: 0.75?A (Including 32kHz RTC)
The datasheet says it’ll operate down to 1.8V. Current will depend on how fast it’s clocked. At 2V and 1MHz, typical supply current for an ATmega328 (or a 328P) is 0.3mA.
Say, where in Michigan are you?
Jack Christesen>> I'm building a small binary clock using SMT LEDs. Do you think that a "3V lithium coin cell" is enough power to do this, or do you think I need the full 5 Volts?
Jack Christensen>> I live in “Le Roy” its south of Cadillac & North of Big Rapids.
It really depends on how long the LEDs will be lit, and how long you want the battery/ies to last. It also depends on the cell you want to use. For example the CR2032 has a maximum discharge rate of 3 mA.
Chris Magagna>> You must be a Pyschic...The "CR2023" is exactly the battery I intend to use. The LEDs will only lit when I push a button, and then go out when the button is released. Kinda like the "indiglo" in some wrist watches.
Chris Magagna>> Oops! thetypo monster strikes again... the battery I'm planning on using is indeed the "CR2032".
Wikipedia says the capacity of a CR2032 is 225 mAh, which means if you pull 0.3 mA out it should last 750 hours (probably less...I don't think you can run them down completely).
So the good (bad?) news is just running your CPU will drain a single cell about a month.
How many LEDs you plan on running, and at what current, will obviously cut into this.
Accuracy may be a problem...the long-term timekeeping of the basic ATMega chip isn't awesome, which is why you see so many people add real-time clock chips (DS1307, DS3231 etc.) to their designs when they want to track time.
Sounds like a cool project though, let us know how it goes
@arduinocrazy2000jb: Perfect application for the 328P’s power-management capabilities (I’d be sure to use a 328P and not a plain 328). Put it to sleep until the button is pushed, it’ll draw < 0.5µA while in power down mode. Either an external RTC could be used, or the 328P can use a 32.768kHz watch crystal directly. Check the datasheet, I’m not entirely clear on this point and have never tried it, but I believe a 32.768kHz crystal can be used either as the system clock, or as a clock source for Timer/Counter2. Either way, a software RTC could then be implemented, and some of the sleep modes allow for the oscillator to keep running so time is properly kept. Run the system clock as slow as possible to minimize current consumption. A 32.768kHz clock would seem to make for a pretty slow system, but if it just needs to keep time, then maybe that’s plenty. So like Chris said, probably the biggest issue then would be to ensure that when the LEDs are on, the instantaneous capacity of the battery is not exceeded.
Interesting project, happy experimenting! Be sure to post your results, I for one would be interested. I’ve got a post around here somewhere that demonstrates power-down mode.
There’s a couple of us in the immediate area here that have been getting together to discuss Arduino and related projects. Le Roy sounds like quite a commute, but keep in touch anyway!
Here's the sleep code I've been using.
It sounds like a nice project. The atmega328p has a special fuse setting for using a 32768Hz crystal. At 32768Hz clock, the current consumption should be fairly low anyway and sleep mode may not reduce it by very much. If you do use sleep mode, you'll also need to wake up the mcu to count timer overflows to do the timekeeping. However, with a 32768Hz crystal, using the 16-bit timer/counter 1 to do the timekeeping, and with the prescaler set to 1024, you only get a timer overflow every 2048 seconds.
If you used a couple of ‘AA’ lithium cells, running the 328 in 32Khz mode you should pretty well get close to the shelf life of the batteries, or about 10 yeas or so.
Chris Magagna>> I'm going to be running 13 smt LEDs, one led on each digital I/O pin.
First off: thank you guys for all your help. I got this project off of www.instructables.com This for a 24hr.(military time) binary clock, I have schematics, the sketch, and most of the parts I need. what I'm trying to do is shrink it down physically to use as a wrist watch. rightnow it's size would require a Gaunlet style piece, that would be heavy, and I suspect fragile too. Beside that, it would look like something the Predator would wear. so I need to shrink it down. So to drive the display, and keep time, I'm using an Arduino Pro Nano /w ATmega328p on board. as you know this is roughly the size of a 28pin dip with .600 spacing on the pins. I have already built a desktop version that runs off a Wallwart, using the Duemilanove. so if I can figure out what lightweight power supply to use with "the nano" the rest is easy.
Oh!..FYI, I'm running the whole kitenkabootle at 16mhz. "standard freq. for the duemilanove."
Here is the link that I based My project from.