<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>Chip,</div><div><br></div><div>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.</div>
<div><br></div><div>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. <br>
<br>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. <br>
<br><div><span class="Apple-style-span" style>Jeff :)</span></div><div><span class="Apple-style-span" style><br></span></div></div><div><br>On Oct 24, 2013, at 10:24, Charles McClelland <<a href="mailto:chip@mcclellands.org">chip@mcclellands.org</a>> wrote:<br>
<br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=windows-1252">First, <div><br></div><div>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. </div>
<div><br></div><div>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 - <a href="https://www.dropbox.com/sh/9qdzturvffr66do/3QMS0SvYHP">here</a> are some pics and a short clip of the sensor in action. <div>
<br></div><div>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 <a href="http://www.lygte-info.dk/pic/Batteries2011/All18650/Capacity-0.2A.png">here</a>). 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 <a href="http://www.intersil.com/en/products/power-management/switching-regulators/integrated-fet-regulators/ISL9110.html">this</a> one. However, I can’t seem to find one in a through-hold package. </div>
<div><br></div><div>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.</div>
<div><br></div><div>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.</div></div><div><br></div><div>Thanks, Chip</div>
<div><br></div><div>PS - thank you for the PCB Carolina’s suggestion - made some great connections to local suppliers and enjoyed the free food.</div></div></blockquote><blockquote type="cite"><div><span>_______________________________________________</span><br>
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