[dorkbotpdx-blabber] Re: solor powered Dorkboard, fact or fiction?

[Jared Boone]

The primary difference I'm aware of between the ATmega168 and the  
ATmega168V is that the "V" will operate down to 1.8V. I don't think it  
consumes any less power than the other part, at a given voltage and  
configuration. But as Laen alluded to, the lower the voltage you can  
operate at, the more juice you can squeeze out of a discharging  
supercap.

I have spent a lot of time getting my Chronulator power consumption  
minimized. Since it's based on an ATmega168V, and is compatible with  
the Arduino tools, I have a lot of knowledge and code you can steal.  
Most of the tricks I employed are simply a matter of putting the chip  
to sleep when it's not doing anything, and making sure the chip never  
does anything it doesn't need to. Doing these things, I am able to  
operate a Chronulator at 1.8V and less than 200 microamps, which turns  
into 360 microwatts. Most of that goes to the meters that indicate the  
time. Take those out, and power consumption is maybe 20 microwatts on  
average.

So what's your project, exactly? You have motors and an LED. What do  
the motors do, how often do they do it, and for how long? The same  
goes for the LED. And what kind of processing/computation will the  
Dorkboard be doing -- how often, and for how long? Depending on your  
answers, we could conceivably get your *average* current consumption  
down into microwatt territory too.

	- Jared

On Mar 31, 2009, at 7:33 PM, Laen wrote:

> A running dorkboard on its own (not running any external components
> like LEDs) is about 20mA at 5V.  I don't know what it would be at 3V.
> I think the Atmega168Vs run a bit less, but I haven't hooked them up
> to a meter.
>
> For the capacitor, I _think_ the math goes like this (someone correct
> me if I'm wrong!)
>
> Volts^2 * Farads = Joules of energy storage.
> Volts * Farads / amps = the amount of time it can put out that amount
> of amps.  In practice, it'll be much lower, because the voltage will
> drop as you drain power.
>
> So:
> a 3V, 1F supercap would run a Dorkboard for:
> 3V*1F / 20 milliamps == 2.5 minutes.
>
> (By the way, google Calculator handles these conversions really well.
> Enter "3V*1F/20 milliamps" into a google search, and you'll get that
> answer.)
>
> -Laen
>
> On Mar 31, 6:36 pm, scott winner <sc... at scenbot.com> wrote:
>> I am looking for some advice or tips.
>> Here is my project,
>>
>> I want to run my Dorkboard on solor
>> power.  Don is setting me up with a 3 volt chip.  That will help a
>> lot.  I am going to model the control after the Solorbotics voltage
>> trigger; solor energy is stored in caps then dumped into the
>> Dorkboard when a critical voltage is reached.
>>
>> So my question for the ether is, what
>> size caps?  How much power needs to be stored to run the Dorkboard?
>> No motor function, just to blink the light.  I know how much to run
>> the motors that will be on a separate circuit.
>>
>> Ok go nuts folks.