See Wormfood’s baud-rate calculator here: http://www.wormfood.net/avrbaudcalc.php
I find that 57600 baud is the maximum at 8MHz, and 115200 at 16MHz. If you’re using the sleep modes then there’s little value in reducing the clock frequency, as the clock is stopped anyway.
Thanks! That’s what I was looking for
Since I’m working on a battery-powered project I measured the effectiveness of the sleep modes on a 16MHz Arduino Uno and on a 8MHz Pro-Mini:
Running the timers adds about 0.4mA to these numbers.
So it looks like the USB interface on the Uno continuously draws about 30mA. The 0.3mA used by the Pro-Mini during power-down is due to the power LED - this could easily be disabled by cutting the PCB track.
Ouch! My application is powered and sometimes controlled through USB, I was planning to use the Arduino Nano for prototyping and create my own PCB based on that later. I guess I can except the 32mA on the Nano too? Or is the FT232 less power hungry?
The Uno’s voltage regulator is very efficient, and the current used hardly depends on whether the regulator is used or bypassed.
The Pro-Mini’s voltage regulator is less efficient (perhaps due to the low currents being used), and the current needed rises by 20-50% if provided via the regulator.
The voltage regulators shouldn’t matter, if my project is powered through USB, right?
Have you thought about just using an ATTiny or ATMega directly on a simpler board without all of the additional Arduino circuitry?
My plan is to prototype with Arduino and produce a PCB if all works out
I actually started out with an Uno but rarely use it any more, having moved on to simpler circuits with ATTiny85, 2313, and the occasional ATMega328. The main benefit here is that you only add what you need for your project; you can even use the Arduino dev environment if you’re so inclined. I’m rather fond of the runtime board from nkc electronics (http://www.nkcelectronics.com/arduino-runtime-board-rev-b.html: $1.99 for the PCB) for the '328 and the tiny dev boards from evilmadscientist.com (http://evilmadscience.com/productsmenu/tinykitlist/112-tiny2313; $2.30 ea in quantities of 5). Or skip the pre-made boards and just protoboard. Or solder directly to the chip . I buy ATTinys in bulk from Mouser ('85s are $1.30 ea in quantities of 25, '2313s $1.53 in same qty) so I always have some on hand. You can make some really neat devices for a couple of bucks and learn quite a bit about the AVR in the process.
Well I think I am in the process of doing that ;), but it’s rather a steep learning curve because of my rather limited electronics knowledge.
For me the Uno was a gateway device - I’m now hooked on the AVR . For the price of a single Uno I can build quite a few devices… My biggest challenge is finishing one project before jumping into the next. This forum is excellent for generating new ideas!
Tell me about it! I started with a simple LED mod and now I have 3 different project ideas constantly floating through my mind It’s like hydra heads
Thanks to everyone for the input,