For Production Atmega 328 Alone?

I am working on a remote sensor project. Optimal battery usage is critical since there is no other source of power. For the finished project, I am thinking about using the 5 volt Arduino Pro http://arduino.cc/en/Main/ArduinoBoardPro or a stand alone Atmega 328 chip.

In other words, the stand alone Atmega 328 chip would be programmed on my Arduino Uno board. Then, I would take it out and wire it to power and a crystal like this https://sites.google.com/site/aaroncrum/aloneatmega328. In terms of saving battery life, I am not sure which is a better approach.

If it were me, I'd design my own circuit. The Arduino Pro still has a linear voltage regulator and a power LED that will continue to draw power even when the MCU is in sleep mode. I'd also consider running at 8MHz so the circuit could then be powered from two AA cells (and the MCU draws less current at lower clock frequencies). Depends on the sensor(s) and the rest of the project, but there are many options.

If "Production" in the subject line implies several copies being made, then for sure I would only consider a custom circuit. But that's just me, I enjoy that part ;)

Thanks for your reply. I am leaning towards the same thing- wire Atmega 328 directly. The sensors needs 5 volt. So instead of making it more complicated with relays, step up power converters etc, I was thinking to just wire the sensor directly.

I was looking one of the TI LM regulators like this- http://www.digikey.com/product-detail/en/LM2937ET-5.0%2FNOPB/LM2937ET-5.0%2FNOPB-ND/212651

Would that be a good power regulator? What do you think of the link I provided on wiring the Atmega directly? It seems a little too simple- not sure if they are missing a pull down resistor.

What is the power source that you think you need a 5V regulator? Any voltage above 5V is just dissipated as heat, hardly optimal use of the critical battery. That circuit, like many, is missing a 10K pullup resistor and 0.1uF caps on the VCC/AVCC pins.

The LM2937 has a pretty high quiescent current, about 2mA. If you don't need over about 200mA total, look at Microchip's MCP1700, its quiescent current is only 1.6µA. Most batteries won't even notice that. There are some small boost regulators that aren't very complicated to use. One I like is the MCP1640. It comes in several versions, a couple of which will pass the battery voltage straight through until an enable signal is asserted, then it boosts to the configured voltage. I use it in a data logger that changes the system clock to 1MHz, then disables the regulator so that the MCU is supplied directly by two AA cells while sleeping. When it wakes, it enables the regulator to supply 3.3V (or 5V) to the sensors, and increases the system clock to 8MHz. I can only seem to get 100-150mA from an MCP1640 though, the numbers in the datasheet seem a bit optimistic, but it works very well for small (low-current) projects.

You are both too good. I was thinking to connect it to a Lantern battery that has a little over 6v. Would I need a voltage regulator to have 5v come out of the Atmega 328 powered by a Lantern battery? . If so, I have found something like http://www.ebay.com/itm/LM2576HV-LM2576-DC-DC-Step-Down-5V-60V-to-1-25V-30V-Adjustable-Power-Supply-Modu-/370833946617?pt=LH_DefaultDomain_0&hash=item56576cf7f9 easier to use. Would be ok in terms of efficiency? I find regulators like the MCP1640 a bit complex to use, but I didn't spend much time with it

I thought that article was missing some resistors and capacitors. Maybe I should just switch back to the Arduino Pro in that case? The led only comes on with Pin 13- which I can avoid using. The cost of the pro is not that much of a factor as ensuring a good launch. It doesn't have to be the very best.

That might be a smart choice for having minimal components. Could always use a small soldering iron and remove the power LED or its current limit resistor to save a little on current draw too.

How much current does the sensor need? The promini MIC5205 regulator is good for 150mA total. http://www.micrel.com/_PDF/mic5205.pdf

That is a good voltage regulator. Also, a good idea to solder out the power LED. Will I even need a voltage regulator for connecting the Arduino Pro directly to a Lantern battery?

The sensor will run very infrequently. Like once every few months for about 10 seconds. The main drain source is the xbee radio. It has to wake up every 15 seconds to look for a signal and go back to sleep.

I wasn't clear in my last post. What I meant is- can I bypass the onboard regulator on the Arduino Pro with my own regulator? Maybe I missed it, but I don't see it on the product webpage ( http://arduino.cc/en/Main/ArduinoBoardPro)

Yes, you can bypass the onboard regulator and feed 5V into the VCC pin.

Perfect. Thank you both! I am all set.

I have a project that sensed temperature and humidity and wrote to an SD card.

http://www.gammon.com.au/forum/?id=12106

That has been going strong now for a couple of months on 3 x AA batteries, writing over 3,800 lines to a file.

The sleep current is around 6 µA which is acceptable as far as I am concerned.

I have another temperature sensor (no SD card though) that is running from 3 x AA batteries and has been going now since March 2013. The voltage from the 3 batteries was 3.97V when it started, and it is still 3.81V which is still well over the level when they are flat (1.2V each, so 3.6V for the three).

http://www.gammon.com.au/forum/?id=11497&reply=5#reply5

General info about power saving: http://www.gammon.com.au/power