I guess measuring the current usage vs power capacity of capacitors was too easy so he decided to do it the hard way.

looking for 3000F so it can run 12 years ?
here it is
http://www.maxwell.com/ultracapacitors/products/large-cell/bcap0650.asp

Rail guns often use ni-cads and various other battery chemistry variants in place of capacitors.

When you need a bunch of current right NOW, big caps just don’t have the right discharge curves.

Nothing compares with flash-over in a big steel cage after something goes wrong – KaPOW!

Hah, “Only 20F…”

That’s a lot of capacitance there buddy!

50 years ago, my high school science teacher was told that a 1F capacitor would have to be the size of a football field!

Of course, that’s surface area, which you can clearly still cram into something small. But its a funny quote considering how common these super and ultracapacitors have become!

Still, 20F is a lot by pretty much anyone’s standards.
-Taylor

farads aren’t amp-seconds, that’s coulombs. Farads are coulombs per volt. Q = It and C = Q/V. super caps have a very high capacitance but a low maximum voltage, so they don’t store ex much energy as it would initially appear, especially since energy stores is proportional to the square of the voltage across the cap

@Ken

It says so right up there:
“To get it ultra low power, the chip is in sleep mode most of the time…”

@cgmark: I lack any kind of measuring device to measure current accurately down to fractions of microamps, and there are more variables than that: the current consumption is very spiky (the controller runs in 32Hz bursts, so what are you actually measuring on an amp meter?), and theres the self-discharge of the caps, and how low the controller can *really* run below the rated 1.8V, etc etc.

So I decided that just running it would give a more meaningful result than a single current measurement.

Others have already made the point that supercaps are ridiculously huge capacitors, but still orders of magnitude smaller than chemical batteries…

Also add to the comments that Microchips product line boasts the lowest sleep current industry wide. Well that was the case when I last researched it. (about a month ago)

maybe its just me , but lately the quantity of posts is high, but its stuff like jamming a hub in a mouse.
Personally I wouldnt call that a hack . But the idea had potential no less to become a hack .

To be a hack I would say you need to add functionality to a device , not add more devices.

This is one of my favorite sites to page threw, Just some constructive criticism.

the problem with just running it without measuring current and voltage during the process is all that it tells you is what that exact code and circuit will do. It doesn’t tell you how that will apply to other circuits powered by the same capacitors. Unless you know what it is consuming at the various times there is nothing to use for comparison.

For measuring something that powers on and off you take a period of time for the measurement and multiply it. Measure what it uses for 1,5,10 seconds and use that to figure out the usage for longer periods.

If you don’t have meters that can measure down to microamps then you can use an opamp to make a current to voltage converter. They can measure into the picoamps range before it gets difficult. Just an opamp and a few resistors.

I thought this was pretty cool and can be turned into something useful quite easily. There sure are a lot of grumpy people reading this website. If you don’t like it then don’t comment.

sorry mah not mha

He should have compared different microcontrollers. That would have been fun!

These guys have pretty big caps.
http://www.goldmine-elec.com/

@ knox

At 10.9kJ those are indeed big capacitors!

Still think its comical so much testing and todoo over this when its not even the best out there. I would be curious to see one of our math wizards do a comparison between the TI chips here and a Microchip XLP. Obviously Im referring to doing the math for both not waiting 3 weeks for the answers.

I suppose the point of this is to benchmark the incredibly well priced launchpad. But still if people are awed by the results it is worth noting that low power is one of Microchips (many) strong points.

So any math wizards wanna break it down?

I’d love to see the same thing done with an ATMega328 and compare!

Actually, I think that specsmanship on power consumption of thing has gotten so complex that running the exact target application on real hardware, for a capacitor charged to a known point, is about the only way to really tell how things are going to work out. C values of far less than 20F are likely to be more useful, though!

The microchip graph claiming to compare “instruction set efficiency” by counting the percentage of instructions that execute “in a single cycle” was particularly laughable. Especially since it included PIC16 and PIC18 families that don’t actually have ANY “single cycle” instructions (unless you’re willing to allow that a cycle is 4 clocks…) I like PICs, but the MSP430 instruction set blows the 8bit PICs out of the water…

At 0.9V VCC, you are going to be badly effected by EMI. I think if someone sneezes close to your product it will fall over.

@smoker_dave

Thanks for making my Pepsi squirt through my nose. lol

Also, IIRC, there’s a way to modify the clock cycle to reduce the effect of EMI. Forgot where I saw it though.

Rallen, I would not trust this kind of technology with a critical function like heartbeat monitoring. However for something like a home automation sensor / actuator which simply turns an IO pin on or off once every so often I feel this is a good simulation.

I do a lot of MSP430 work at uni, and the correct way to measure current in a setup like this is to take the integral of the current. In his case it should be an easy step function, so effectively:

(i_sleep * %_sleeping) + (current_wake * %_awake) = i_total. Unfortunately the current draw is a function of Vcc in CMOS tech, so it varies a bit with the current level of the caps and stuff, but it should be close enough for a first order approximation. The MSP430s are fairly power efficient if you use the low power modes as Ken did, and with 20F backing it, I wouldn’t be surprised it runs for a very very long time.
Hell, I bet the caps are self-discharging more current than the MSP430+LCD is drawing.

Ωsmoker_dave: Don’t see why the rail voltage should have any bearing on susceptibility to interference. Care to clarify that?

@Torque i am working on a way to reuse these panels for active camouflage.. only problem is the number required.

right now ti is more efficient than micro but epson’s soon to be released chip will have some serious benefits such as rfid, io, and charge consumption.

> (i_sleep * %_sleeping) + (current_wake * %_awake) = i_total.
It’s nowhere near that simple anymore. N different sleep modes, M different clocks for different parts of the chip, individually powerable peripherals; the complexity goes on an on.
For example, TI claims that their chips “wake up” so much faster than most micros that this results in significant power savings…

rcx: “specifically, 20F at 2.7V will store 20 x 2.7^2 = 145.8 coulombs. a 1000 mAh battery will store 1000 x10^-3 x 3600 = 3600 coulombs, or 25 times as much.”
Wrong, wrong, wrong. 20F * 2.7V (NOT squared) = 7.40C

Well… I think this comment thread helps justify why I decided that just running it would be the most effective measurement.

honestly, lets stop fighting over whose right or wrong and see the results of how long it lasted, then hook up the 2 caps to an arduino and count how many seconds it lasts

@Ken – If you would have just done math, and made a video of you writing it all out on a whiteboard… everyone would just be saying “oh, but don’t forget about the leakage current” and “oh you’re so stupid because you calculated the charge, assuming you could ever really fully charge those caps” and “I already tested this on Microchip’s XLP series micros and they’ll totally PWN your MSP!”

What you did was what most normal people would do, an experiment to see WTF really happens. Rock on Ken, I know you’ve opened some eyes with your demonstration. I’m sorry but people don’t have the patience for boring posts involving math… just show us the results! Then after you’ve sucked us in with results, go ahead and show us all of the little bits that make it work – if you want. Or we can just read all of the attempts at calculating something here in the comments… although nothing I read tells me as much as your video.