[TriEmbed] Power Questions

Thu Oct 24 10:36:11 CDT 2013

I have used two circuits for several years. The first is a buck-boost from
Linear Technologies. LTC3531. This is relatively efficient, and operates
from an input of 1.8v to 5.5v. Thus you can use it with several battery
combinations. I have used it with 4 "AA" as they rapidly discharge down to
the 1.35 range and the margin in the device will tolerate the over voltage
condition. I have also used it with to 2 "AAA".

If you want to add in a Li-Ion cell, I would suggest you use the Linear
Tech LTC4055. This will allow for recharge from either a USB or wall wart.
The output from this device feeds the LTC3531.

If interested in either of these solutions I have some personal boards laid
out to use them.

Jim Carlson

On Thu, Oct 24, 2013 at 11:07 AM, John Vaughters <jvaughters04 at yahoo.com>wrote:

> 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<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.
>
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-- 
Thanks,
Jim Carlson
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