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September 10, 2011
Check out what you can do with a Beaglebone and other open-source project ideas at http://knek-tek.me
about 13 hours ago
Unfortunately after spending nearly two years in storage, my sensor no longer works, even after placing it in a very humid container for a day. It is stuck in Diagnostic mode and only gives RH=99.94%, Temp=124.98, no matter what. :-(
Is it possible that one of these cannot be reconditioned and I have to throw it out? Your guide says >50% RH for 5 hours, which I did.
News - Simple Solar Power
In the figure where you show the capacitors hanging off the Vin pin, and you had to use a diode to prevent backflow into the solar panel, you could instead put the capacitors coming off the Vcc pin (Vout on the actual chip) and like Fig 11 on p. 16 of the 3588’s datasheet you would NOT need a diode. The LTC3588-1 is able to have huge capacitance on its output without the need for a blocking diode…apparently. Haven’t tried it myself.
Am I wrong?
The self discharge at room temperature seems to be pretty bad from what I just measured. I had two in series with 2.08V on them, and they proceeded to lose about 1mV/s. This is when they weren’t hooked to anything- I even removed the multimeter probes for a while to make sure those weren’t draining current.
I’m not very happy with that since I have another 1F supercap that is pretty good at holding a charge, it’s a PowerStor Aerogel PB Series, and only loses about 50mV per hour. I bought these Sparkfun ones to power a solar powered device over night so they’re not going to work, and I need to buy some better ones off digikey. :-(
I did some calculations to compare these to the PowerStor one, and losing 1mV off a 1F capacitor is 500nJ of energy lost. But losing 1mV off a 5F capacitor is 2.5uJ, 5x more energy lost, which makes sense. Equation is E=(½)C(V2)
EDIT: I tested this again later in the day and now they seem to be holding charge much better, even using the same multimeter and everything. Weird, maybe they just needed to be “broken in”? Or maybe the charge loss at higher voltages is much higher than at lower voltages?
about 3 weeks ago
I used this thing and the LTC3588 buck converter (also sold on Sparkfun in a different form than what I used) to make a solar-powered web server
The example code that is available in the Arduino library is fantastic, and the intergration with Phant.io is pretty easy too.
Vin2 and SW don’t look like a user would need access to them anyway. (I say this having not yet used the chip.)
However renaming Vout to Vcc and PGOOD to EN is annoying, but I’m guessing sparkfun did it to try and provide consistency with other boards for newbies wondering what-to-hook-up-to-what.
This chip has internal rectification between PZ1 and PZ2. Check the datasheet, page 7 block diagram.
You would need to look at the Joules of energy you’re getting- specifically how long the light flashes last, and how much voltage and current you get from each one. Current * Voltage = Watts, Watts * Time = Joules. Find out how many watts of energy you need on the output, and for how long, that gives you the amount of joules you need and then calculate backward from that.
If the flashes are very quick and have a low duty cycle then you probably won’t be able to power anything from them. But if they’re frequent enough you could have those flashes cause the solar panel to put charge on a capacitor and then work from there. This part would be good at that since it sleeps until enough charge is on the input cap to efficiently convert it.
News - IoTuesday: Why IoT Is Abo…
about a month ago
No, they don’t. First, anytime you use the “security through obscurity” mindset you have no security. Secondly, one of the things which will be standardized is proper security practices and technologies (meaning good, widely peer-reviewed encryption methods, and the correct means of implementing that encryption). This means that greater standardization will lead to greater security.
Security is hard, so having a large consortium create the gold standard and ensuring that all device manufacturers follow that standard will increase the security of the whole system. A fractured archipelago of hacked-together solutions creates a system with tremendous weaknesses at all points.
about a month ago
Finally finished building a project with this board. Hope that the layout mistakes I made and the software I got working are useful for others: link to blog post (software and PCB files will be uploaded in a few days)
about 4 months ago
Note that the switch on the board doesn’t cut power from the USB cable to the 5V rail, it only enables the 3.3V rail. So if you’ve got stuff hooked up to the 5V pin, that will be powered as long as the USB cable is in.
I would have preferred the power switch to be placed just after the diode so that it cuts both the 5V and 3.3V rails. Stuff can get damaged if the 5V rail is on but 3.3V is not, for example if this board is hooked up to a circuit using both voltage levels.
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