[TriEmbed] Jeff's Response

Thu Oct 24 19:52:01 CDT 2013

Jeff, 

I think you are on to something there.  My input is analog as I need to be able to set a “threshold” value using a trimpot once the sensor is attached to the bridge (some are more rickety than others).  But, I have been focused on how much voltage the ATTiny84 can take, not how little.  My ATTiny looks like it would work with as little as 2.7V.  So, I should be able to rewire my 18650 battery holder to put the cells in parallel not series.  Then the voltage would go from 4.2 to 3.4 volts.  I am not sure what that would do to my AREF so need to look at whether there is an “internal” option.  

Thanks,

Chip

On Oct 24, 2013, at 11:07 AM, triembed-request at triembed.org wrote:

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> Today's Topics:
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>   1. Power Questions (Charles McClelland)
>   2. Re: Power Questions (Jeff Highsmith)
>   3. Re: Power Questions (John Vaughters)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Thu, 24 Oct 2013 10:23:58 -0400
> From: Charles McClelland <chip at mcclellands.org>
> To: triembed at triembed.org
> Subject: [TriEmbed] Power Questions
> Message-ID: <C43887D3-D32D-4BEB-8B0F-3B43180C129B at mcclellands.org>
> Content-Type: text/plain; charset="windows-1252"
> 
> First, 
> 
> I want to thank you all for the help I have received so far.  I am working with a group that is building and maintaining trails in the woods around the RDU airport.  We are talking to the state and county parks folks and need some solid data on trail utilization to support your requests.  I am building a simple sensor to count the bike traffic per hour on a trail in the woods over a week.  
> 
> Thanks for Paul?s suggestion, I went with a Piezo sensor attached to the underside of a wooden bridge and write the counts every 3.6M clock cycles to EEPROM.  Each count takes just one byte (never more than 253 bikes in an hour) so the setup should last for 21 days before taking up all 512 Bytes of memory.  I tested it last weekend and it worked like a charm - here are some pics and a short clip of the sensor in action.  
> 
> Now the problem and a request for help.  I am currently using a 9V battery (typical capacity 310 mAH) and a 7805 linear regulator.  With a fresh battery, I am only getting about 24 hours of operation.  I have some high capacity 18650 LiON batteries which operate at 3.6 volts (voltage curve here).   Which I can put in series using a simple holder.  The problem is that I will not get nearly the full capacity of the batteries (3400 mAH each) before I am below the drop-out voltage of the 7805.  At the PCB Carolinas conference yesterday - I asked around and was delighted to hear about a ?high efficiency buck boost regulator? like this one.  However, I can?t seem to find one in a through-hold package.  
> 
> I also considered putting a diode in series with the 18650 batteries to knock off a volt.  However,  looking at the voltage curves, it seems that I would exceed the 6V maximum the Atmel data sheet specifies for the ATtiny84 when the batteries are freshly charged.
> 
> I want to keep this circuit cheap and small as it will be buried in the dirt for a week at a time and may well get stolen.  Any suggestions would be appreciated.
> 
> Thanks, Chip
> 
> PS - thank you for the PCB Carolina?s suggestion - made some great connections to local suppliers and enjoyed the free food.
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> ------------------------------
> 
> Message: 2
> Date: Thu, 24 Oct 2013 10:59:34 -0400
> From: Jeff Highsmith <jeff at jeffhighsmith.com>
> To: Charles McClelland <chip at mcclellands.org>
> Cc: "triembed at triembed.org" <triembed at triembed.org>
> Subject: Re: [TriEmbed] Power Questions
> Message-ID: <-8121659943955316096 at unknownmsgid>
> Content-Type: text/plain; charset="windows-1252"
> 
> Chip,
> 
> If you could run the ATTiny84 directly from a battery (with a voltage
> within the '84's specs), you wouldn't have to lose power as heat knocking
> the 9V down to 5V.
> 
> Another way to save significant power would be to have the ATTiny use it's
> low power modes. This won't be effective if there is still a linear
> regulator in the circuit. If you had a sensor that acted like a switch or
> had a digital output, you could have it wake the '84 upon sensing. The '84
> could log a bike and go back to sleep. You would use the interrupts or even
> the reset pin for this. A year or two ago, I made my sons' a traffic light
> using three LEDs (green, yellow, red) in Radio Shack's smallest project
> box. The circuit is just an ATTiny85 (maybe the low voltage version)
> powered by two AA cells. The "on" button is actually tied to the reset pin,
> so it resets the '85 when pushed (I was in too big of a hurry to learn
> interrupts that day). The program tells the '85 to run the traffic light
> for two minutes (average toddler attention span) and then go into low power
> sleep. In the couple years of play and (mostly) standby, I can't remember
> ever changing the battery.
> 
> I'm not sure what would happen to the memory when the battery eventually
> drops below the '84's minimum, but maybe you could gracefully remove power
> completely at that point using some discrete components.
> 
> Jeff :)
> 
> 
> On Oct 24, 2013, at 10:24, Charles McClelland <chip at mcclellands.org> wrote:
> 
> First,
> 
> I want to thank you all for the help I have received so far.  I am working
> with a group that is building and maintaining trails in the woods around
> the RDU airport.  We are talking to the state and county parks folks and
> need some solid data on trail utilization to support your requests.  I am
> building a simple sensor to count the bike traffic per hour on a trail in
> the woods over a week.
> 
> Thanks for Paul?s suggestion, I went with a Piezo sensor attached to the
> underside of a wooden bridge and write the counts every 3.6M clock cycles
> to EEPROM.  Each count takes just one byte (never more than 253 bikes in an
> hour) so the setup should last for 21 days before taking up all 512 Bytes
> of memory.  I tested it last weekend and it worked like a charm -
> here<https://www.dropbox.com/sh/9qdzturvffr66do/3QMS0SvYHP> are
> some pics and a short clip of the sensor in action.
> 
> Now the problem and a request for help.  I am currently using a 9V battery
> (typical capacity 310 mAH) and a 7805 linear regulator.  With a fresh
> battery, I am only getting about 24 hours of operation.  I have some high
> capacity 18650 LiON batteries which operate at 3.6 volts (voltage
> curve here<http://www.lygte-info.dk/pic/Batteries2011/All18650/Capacity-0.2A.png>).
> Which I can put in series using a simple holder.  The problem is that I
> will not get nearly the full capacity of the batteries (3400 mAH each)
> before I am below the drop-out voltage of the 7805.  At the PCB Carolinas
> conference yesterday - I asked around and was delighted to hear about a
> ?high efficiency buck boost regulator? like
> this<http://www.intersil.com/en/products/power-management/switching-regulators/integrated-fet-regulators/ISL9110.html>
> one.
> However, I can?t seem to find one in a through-hold package.
> 
> I also considered putting a diode in series with the 18650 batteries to
> knock off a volt.  However,  looking at the voltage curves, it seems that I
> would exceed the 6V maximum the Atmel data sheet specifies for the ATtiny84
> when the batteries are freshly charged.
> 
> I want to keep this circuit cheap and small as it will be buried in the
> dirt for a week at a time and may well get stolen.  Any suggestions would
> be appreciated.
> 
> Thanks, Chip
> 
> PS - thank you for the PCB Carolina?s suggestion - made some great
> connections to local suppliers and enjoyed the free food.
> 
> _______________________________________________
> Triangle, NC Embedded Computing mailing list
> TriEmbed at triembed.org
> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> TriEmbed web site: http://TriEmbed.org
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> ------------------------------
> 
> Message: 3
> Date: Thu, 24 Oct 2013 08:07:41 -0700 (PDT)
> From: John Vaughters <jvaughters04 at yahoo.com>
> To: Charles McClelland <chip at mcclellands.org>,	"triembed at triembed.org"
> 	<triembed at triembed.org>
> Subject: Re: [TriEmbed] Power Questions
> Message-ID:
> 	<1382627261.86664.YahooMailNeo at web163004.mail.bf1.yahoo.com>
> Content-Type: text/plain; charset="utf-8"
> 
> Chip,
> 
> That is some mighty impressive work there. The woods around the Airport would be great for bike trails. I will make a suggestion, but it is completely untested, so I would be curious to your results. I have often used Buck regulators from old car Cell phone chargers to pull power for 5 volt electronics in cars. Just about everyone has 5-10 laying around the house alone. You can break them open and reduce the space by taking out the electronics. They are basically designed to provide 5-6V from a 12-18V source. So you could see what they provide with 9V first, but if that doesn't cut it, use two 9V for an 18V source. I still use a 7805 to get it to 5V, I prefer to prevent over voltage from the Buck.?
> 
> This may or may not help you, but the cost is really cheap. Walmart even sells them for about $5. The main problem is that these buck regulators are not the most efficient and they get worse as the difference in voltage between source and sink rise.?
> 
> If you go this route, let us know how it works out for you.
> 
> Thanks,
> 
> John Vaughters
> 
> 
> 
> On Thursday, October 24, 2013 10:24 AM, Charles McClelland <chip at mcclellands.org> wrote:
> 
> First,?
> 
> I want to thank you all for the help I have received so far. ?I am working with a group that is building and maintaining trails in the woods around the RDU airport. ?We are talking to the state and county parks folks and need some solid data on trail utilization to support your requests. ?I am building a simple sensor to count the bike traffic per hour on a trail in the woods over a week. ?
> 
> Thanks for Paul?s suggestion, I went with a Piezo sensor attached to the underside of a wooden bridge and write the counts every 3.6M clock cycles to EEPROM. ?Each count takes just one byte (never more than 253 bikes in an hour) so the setup should last for 21 days before taking up all 512 Bytes of memory. ?I tested it last weekend and it worked like a charm -?here?are some pics and a short clip of the sensor in action. ?
> 
> Now the problem and a request for help. ?I am currently using a 9V battery (typical capacity 310 mAH) and a 7805 linear regulator. ?With a fresh battery, I am only getting about 24 hours of operation. ?I have some high capacity 18650 LiON batteries which operate at 3.6 volts (voltage curve?here).?? Which I can put in series using a simple holder. ?The problem is that I will not get nearly the full capacity of the batteries (3400 mAH each) before I am below the drop-out voltage of the 7805. ?At the PCB Carolinas conference yesterday - I asked around and was delighted to hear about a ?high efficiency buck boost regulator? like?this?one. ?However, I can?t seem to find one in a through-hold package. ?
> 
> I also considered putting a diode in series with the 18650 batteries to knock off a volt. ?However, ?looking at the voltage curves, it seems that I would exceed the 6V maximum the Atmel data sheet specifies for the ATtiny84 when the batteries are freshly charged.
> 
> I want to keep this circuit cheap and small as it will be buried in the dirt for a week at a time and may well get stolen. ?Any suggestions would be appreciated.
> 
> Thanks, Chip
> 
> PS - thank you for the PCB Carolina?s suggestion - made some great connections to local suppliers and enjoyed the free food.
> _______________________________________________
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> TriEmbed at triembed.org
> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
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