AVR-Chat

Hi Folks,

I'm working on a battery powered consumer product that will use a 3V
button cell.  I think we've settled on the CR2032 which has a capacity
of 225uAH.  Our circuit will use an ATtiny13 @ 1MHz along with a few
other items.  The total current consumption is about 2.65ma when
always ON.  I think I can reduce that to about 460uA by cycling the power.

My question to the group - can I just use the battery or do you think
I'll need some type of regulator?  

The application will be mostly in the off state.  I'm planning to have
the unit ON after being plugged into the  item to be controlled and
then after 10 minutes go into the low power mode and then after 30
minutes turn itself off.

Thanks,

Richard Cooke

On 11/29/06, Richard Cooke <rcooke@digitalwavelength.com> wrote:
>
> Hi Folks,
>
> I'm working on a battery powered consumer product that will use a 3V
> button cell.  I think we've settled on the CR2032 which has a capacity
> of 225uAH.


Isn't that mAH?  1000 times more.

My question to the group - can I just use the battery or do you think
> I'll need some type of regulator?


What does the data sheet tell you?
The battery will deliver 3.1 - 3.2V when new, and drop off as it ages.
2.0V is typically considered "dead".

The application will be mostly in the off state.  I'm planning to have
> the unit ON after being plugged into the  item to be controlled and
> then after 10 minutes go into the low power mode and then after 30
> minutes turn itself off.


Is there a real advantage to that low power interval?


[Non-text portions of this message have been removed]

Opinion without direct experience: you probably don't need
an additional regulator. You will need some good bypass
caps, size and value depending on the nature of the loads
driven by the micro. This is because the output resistance
of small batteries like this tends to be higher than you
might expect.

I assume that when you say "power cycling", you mean
periodically putting the micro into a low power mode? Or,
are you physically removing power?

Jim


On Thu, 30 Nov 2006 00:27:25 -0000
 "Richard Cooke" <rcooke@digitalwavelength.com> wrote:
> Hi Folks,
> 
> I'm working on a battery powered consumer product that
> will use a 3V
> button cell.  I think we've settled on the CR2032 which
> has a capacity
> of 225uAH.  Our circuit will use an ATtiny13 @ 1MHz along
> with a few
> other items.  The total current consumption is about
> 2.65ma when
> always ON.  I think I can reduce that to about 460uA by
> cycling the power.
> 
> My question to the group - can I just use the battery or
> do you think
> I'll need some type of regulator?  
> 
> The application will be mostly in the off state.  I'm
> planning to have
> the unit ON after being plugged into the  item to be
> controlled and
> then after 10 minutes go into the low power mode and then
> after 30
> minutes turn itself off.
> 
> Thanks,
> 
> Richard Cooke
> 

---------------------------------------------------------------
The Think Different Store
http://www.thinkdifferentstore.com/
For All Your Mac Gear
---------------------------------------------------------------

Hello Mr. Richard Cooke,

Here is a checklist provided by our area Atmel FE Mr. Eric Feign for those
doing low power work. It has some good points. It seems that there are some
other areas of your design to be considered as the processor must do
something and there may be other chips/circuits to do something that may
dictate whether you need regulation or not. Using a CR2032 type small coin
battery requires careful attention to power needs as 250mAH is pretty thin
so the list below will be important.

Give the group more info into what you want to accomplish and there will be
lots of help flow...

Jim

Low Power Checklist

1. Operate at lowest voltage possible since power is proportional to V^2.
2. Depending on application:
  A. Sleep as much as possible then operate at as a high a frequency as
possible in order to get back to sleep sooner.
  B. For applications that may not be able to take advantage of sleep,
operate at as low a frequency as possible since    power is proportional to
F.  Can take advantage of Clock Prescale Register CLKPR.  Can use low
frequency crystal or 128kHz internal RC.
3. Turn off peripherals not in use.  Take advantage of Power Reduction
Register PRR if available.
4. Use Low Power Crystal Oscillator fuse setting for applications requiring
crystal timing accuracy in low noise environments.
5. Enable internal pull-up on unused inputs; use external pull-ups if low
power during reset is important.
6. Disable Analog Comparator when not required (ACD bit in ACSR).
7. Disable Watchdog Timer if not required.
8. Disable Analog to Digital Converter if not required (ADEN bit in ADCSR,
If sleeping in other than Idle or ADC Noise Reduction modes, set ADEN=0
before sleep.
9. Use Digital Input Disable Registers (DIDRx) for those dedicated ADC
analog inputs.
10. Disable Brown Out Detect if not required.
11. Disable On Chip Debug system with DWEN fuse if not required.


----- Original Message ----- 

From: "Richard Cooke" <rcooke@digitalwavelength.com>
To: <AVR-Chat@yahoogroups.com>
Sent: Wednesday, November 29, 2006 4:27 PM
Subject: [AVR-Chat] 3V supply - need regulator?


> Hi Folks,
>
> I'm working on a battery powered consumer product that will use a 3V
> button cell.  I think we've settled on the CR2032 which has a capacity
> of 225uAH.  Our circuit will use an ATtiny13 @ 1MHz along with a few
> other items.  The total current consumption is about 2.65ma when
> always ON.  I think I can reduce that to about 460uA by cycling the power.
>
> My question to the group - can I just use the battery or do you think
> I'll need some type of regulator?
>
> The application will be mostly in the off state.  I'm planning to have
> the unit ON after being plugged into the  item to be controlled and
> then after 10 minutes go into the low power mode and then after 30
> minutes turn itself off.
>
> Thanks,
>
> Richard Cooke
>
> <<< snip >>>

Oops - I meant 225mAH , sorry about that.  Regarding the 10 minutes of
ON time.  We haven't nailed the times down - 10 minutes is an
estimate.  We might have to throttle down to a much slower speed for
30 minutes to wait for the signal from the IR receiver module.  If
nothing has been detected after that we'll shut down.

--- In AVR-Chat@yahoogroups.com, "David VanHorn" <microbrix@...> wrote:

>
> On 11/29/06, Richard Cooke <rcooke@...> wrote:
> >
> > Hi Folks,
> >
> > I'm working on a battery powered consumer product that will use a 3V
> > button cell.  I think we've settled on the CR2032 which has a capacity
> > of 225uAH.
> 
> 
> Isn't that mAH?  1000 times more.
> 
> My question to the group - can I just use the battery or do you think
> > I'll need some type of regulator?
> 
> 
> What does the data sheet tell you?
> The battery will deliver 3.1 - 3.2V when new, and drop off as it ages.
> 2.0V is typically considered "dead".
> 
> The application will be mostly in the off state.  I'm planning to have
> > the unit ON after being plugged into the  item to be controlled and
> > then after 10 minutes go into the low power mode and then after 30
> > minutes turn itself off.
> 
> 
> Is there a real advantage to that low power interval?
> 
> 
> [Non-text portions of this message have been removed]
>

Hi Jim,

Yes, by power cycling I meant to put it into a lower power mode.  I am
also going to periodically go back to full speed to see if there is a
signal from the IR reciever module.  If there is then it's back to
full power.

I'm not sure I understand your comment about the need for bypass caps.
 The circuit will only be pulling 2 lines low for approximately 150 ms
and then back to the supply voltage.  The unit we plug into is also
battery powered (5V) so the inputs will have to handle that.

Thanks,

Richard

--- In AVR-Chat@yahoogroups.com, "Jim Wagner" <jim_d_wagner@...> wrote:

>
> Opinion without direct experience: you probably don't need
> an additional regulator. You will need some good bypass
> caps, size and value depending on the nature of the loads
> driven by the micro. This is because the output resistance
> of small batteries like this tends to be higher than you
> might expect.
> 
> I assume that when you say "power cycling", you mean
> periodically putting the micro into a low power mode? Or,
> are you physically removing power?
> 
> Jim
> 
> 
> On Thu, 30 Nov 2006 00:27:25 -0000
>  "Richard Cooke" <rcooke@...> wrote:
> > Hi Folks,
> > 
> > I'm working on a battery powered consumer product that
> > will use a 3V
> > button cell.  I think we've settled on the CR2032 which
> > has a capacity
> > of 225uAH.  Our circuit will use an ATtiny13 @ 1MHz along
> > with a few
> > other items.  The total current consumption is about
> > 2.65ma when
> > always ON.  I think I can reduce that to about 460uA by
> > cycling the power.
> > 
> > My question to the group - can I just use the battery or
> > do you think
> > I'll need some type of regulator?  
> > 
> > The application will be mostly in the off state.  I'm
> > planning to have
> > the unit ON after being plugged into the  item to be
> > controlled and
> > then after 10 minutes go into the low power mode and then
> > after 30
> > minutes turn itself off.
> > 
> > Thanks,
> > 
> > Richard Cooke
> > 
> 
> ---------------------------------------------------------------
> The Think Different Store
> http://www.thinkdifferentstore.com/
> For All Your Mac Gear
> ---------------------------------------------------------------
>

----- Original Message ----- 

From: "Richard Cooke" <rcooke@digitalwavelength.com>
To: <AVR-Chat@yahoogroups.com>
Sent: Thursday, November 30, 2006 12:27 AM
Subject: [AVR-Chat] 3V supply - need regulator?


> Hi Folks,
>
> I'm working on a battery powered consumer product that will use a 3V
> button cell.  I think we've settled on the CR2032 which has a capacity
> of 225uAH.  Our circuit will use an ATtiny13 @ 1MHz along with a few
> other items.  The total current consumption is about 2.65ma when
> always ON.  I think I can reduce that to about 460uA by cycling the power.
>
> My question to the group - can I just use the battery or do you think
> I'll need some type of regulator?
>
> The application will be mostly in the off state.  I'm planning to have
> the unit ON after being plugged into the  item to be controlled and
> then after 10 minutes go into the low power mode and then after 30
> minutes turn itself off.

It;s quite common not to use a regulator when using those cells with the 
very low power MSP430 MCUs. In fact, that's what I'm doing in an application 
that will spend most of its time in sleep mode.

Leon
--
Leon Heller, G1HSM
Suzuki SV1000S motorcycle
leon.heller@bulldoghome.com
http://www.geocities.com/leon_heller

The mode you describe makes good bypass caps even more
important. As the battery discharges, its output resistance
increases. Adding something like 47uf across the battery
allows it to charge slowly to the maximum possible voltage
while the micro is in low power mode, then deliver that
150ms pulse of current and do it further into the discharge
cycle.

Your need to interface to 5V is perhaps even greater a
problem. I would suggest looking at some of the Linear Tech
"power path" switches. This lets the thing you plug into
provide the power for the micro and its circuits at 5V.
That reduces power  consumption AND provides simple voltage
interfacing. Then, the battery only supplies power when it
is unplugged.

Jim


On Thu, 30 Nov 2006 04:16:09 -0000
 "Richard Cooke" <rcooke@digitalwavelength.com> wrote:
> Hi Jim,
> 
> Yes, by power cycling I meant to put it into a lower
> power mode.  I am
> also going to periodically go back to full speed to see
> if there is a
> signal from the IR reciever module.  If there is then
> it's back to
> full power.
> 
> I'm not sure I understand your comment about the need for
> bypass caps.
>  The circuit will only be pulling 2 lines low for
> approximately 150 ms
> and then back to the supply voltage.  The unit we plug
> into is also
> battery powered (5V) so the inputs will have to handle
> that.
> 
> Thanks,
> 
> Richard
> 
---------------------------------------------------------------
The Think Different Store
http://www.thinkdifferentstore.com/
For All Your Mac Gear
---------------------------------------------------------------