10/20/2017 at 20:06 •
John So, this is a first for me, should we start with those questions in the sheet?
Shayna Usually we'll get a few more coming up during the discussion, but unless they're a pretty quick one-liner answer we generally try to save them for after the question sheet is completed.
Sophi Kravitz hi everyone!
Shayna And if you're able to stay longer, the open discussion after is usually pretty fun. :)
Shayna Here's the question sheet once again, for folks who just joined in: https://docs.google.com/spreadsheets/d/12pdRwse7w_fa37hgPZezdCcVQ2WvNw--9SwoBAAFy-M/edit?usp=sharing
kristina panos Hi everyone
Zalán Meggyesi Hi!
Audi McAvoy Hello everyone
John Ah sorry, closed the chat for a couple of minutes
John Alright it's now 9pm in Rotterdam
John (where I'm based)
kk.bedead is there any kind of command interface available here? #help
John As a background, I'm one of two founders of a R&D company (TWTG) based here.
John You might know us from the Things Network (LoRa WAN) hardware
Andrey is the chat getting recorded?
Jordan Bunker I'll be posting a transcript of the chat afterward :)
Zalán Meggyesi oh cool!
Zalán Meggyesi thanks in advance!
John As a company focusing on embedded connected hardware we are working with different forms of Energy harvesting
John We definitely don't know everything, but will try to share some experiences
John insights etc that we gatherd
John So i guess that's it in short,
John are we ready to start this madness?
John Yes sure
John Should we start with the sheet?
kk.bedead give us some overview of existing methods pls
John I think both are usefull
John read them earlier, great to get to know what's happening in the area
John (we prefer hackaday ofcourse)
John Next question I liked
John We love the opensource Ruuvi platform
John It's a nice platform to start thinkering,
Todd Pollman Thinkering is what I do before tinkering.
John Let me combine this with the next question
John Sorry meant the one after that
John In a ultra low power solution it's good practice to switch off a lot of subsystems with loadswitches
Paul Crouch Low current measurement: Dave's uCurrent?
John SO to measure the current in the easiest way you could actually use a lot of default solutions, but just make sure to disconnect them completely
John A lot of the default energy harvesting IC's normally have these build in anyway
zakqwy So the IC has switches built in to switch loads.. but how do you measure total draw, other than (a) an expensive bench meter or (b) a uCurrent from Dave?
John As a bench setup we use the uni-T UT61E
John It's quite affordable for these kind of applications
John More expensive, but more accurate is a Brymen mb869s
John bonus points
John Firmware, correct
John You will need something different than your normal approach
kk.bedead well, obviously
John We use a scheduler approach
John This will take the available amount of energy in account
John "Energy based scheduler" (time for a project page)
Josh Cole interesting!
John Should we finish the questions and then circle back to this if interested?
Shayna Next up from @Shantam Raj : "With reference to https://hackaday.io/project/20523-sun-self-sustained-ultralow-power-node , what more can you suggest to extract as much energy as possible and to reduce power wastage in schottky diodes, leakage current in programming resistors, leakage in digital electronics especially the I2C bus?"
Shantam Raj Sure
John We like your project! Haven;t seen it before
John Go on!
John But on your question:
John good practise in ultralowpower design would be: choose low-power components, apply load-switches, apply high-impedances where possible, etc.
John Seems trivial
John For your design using loadswitches could already make some difference
John Diodes with low drop helps
John In situations with sleepcurrent a DC/DC might not be ideal
Shantam Raj Already done as much as i could. If you go through the schematics and components i have used you wll realize that i made sure leakages are minimum, voltage drops are minimum etc. But i always feel there is some room for improvement. I just graduated a couple of months ago and i feel like i don't have much expertise.
John These might be good for you: HSMS-2850 250mV
John Look into them
Shantam Raj Oh, is that so? I am of the opinion that DC/DC are more efficient than LDOs
John A LDO sometimes could be more efficient
John depends on your setup etc of course
Shayna Another from @shantamraj "What are some really efficient commercial/academic products out there that implement energy harvesting and should be on our lookout to learn more about the frontiers in energy harvesting? (From the point of view of rather small digital electronics)"
John do's and dc-dc converters have a quiescent current, if you do not require a precise voltage, you can use ordinary diodes to drop the voltage. The big advantage is that as diodes are placed in series, they can not consume a (quiescent) current.
John Enocean have great modules as well
John Answers this your questions?
Shantam Raj Yes
John How would you handle harvesting various ambient energies at once? Say for example, 60Hz, 1800Mhz, and 5GHz?
Charlie Lindahl Have you seen any energy harvesting happening on watches? I have a Pebble and was going to use their API & hardware connector for some sort of external power, but then of course Fitbit bought Pebble and killed off the platform.
John Please clarify, I think you mean RF harvesting correct? Or are you thinking about communication?
Charlie Lindahl I'd still like to find a way to "energy harvest" for my Pebble and whatever my next watch is.
Charlie Lindahl [Sorry, will get to my questions after you finish the thread you're on]
Shayna Ah sorry
Soul_Est Yes, John, I meant RF harvesting.
John it;s more focused on the battery internally, getting more of a "hybrid" solution, charging the battery
John But yeah, why not.
John use a coil for the 60 hz and a multiband antenna for 1800 and 5 GHz with a harvester
John or use a piezo and attached to a magnet near an ac source, this can yield pico to micro watts
John sorry nano wats
John But talking RF harvesting, best results are in the GSM bands
John or in the 2.4 ghz if you can control the environment
John Result is very low, but constant. Making it very interesting
John check this out: https://hackaday.com/2017/10/02/fm-snake-feeds-off-radio-waves/
John (hackaday reference bonus points)
kristina panos I still want to make one of those
Shayna From @ecomer : "Curious about ambient energy harvesting in very rural areas with little stray electronic noise, especially when solar is difficult, especially storing adequate solar energy to last through the night. Especially curious when solar is NOT an option (remember the very rural low electronic noise setting)"
Soul_Est Thank you, John. =)
John Care to share a little bit more about the application?
John Normally solar with a (super) cap setup could work?
ecomer Clarification: My project currently uses 2V solar with boost and AA battery storage. I'd like to eliminate the solar, if possible, but not sure what ambient energy is available in a very rural environment. Stray RF from the ether would seem to be all that there is once solar is eliminated.
John Well, if you want to go crazy: maybe get energy from temperature difference with the ground: using a peltier element?
John (try it for science, throw it away, use solar)
John Why don;t you want to use solar?
John How much do you think you'll need?
ecomer Any idea just how much energy can be harvested from the sky in a rural setting?
John Maybe a windmill?
ecomer 50ma hourly bursts, sleeping between
John bursts of how long?
John This could be done with a relative small solar panels
John We have some good experience with the ones from IXYS.
John Combine these with a good supercap setup and that could work
ecomer That's what I'm doing now - small 2V panels. Seeking alternatives
John With an 3.7v 1 mA hour solar panel, there would be enough energy
John IXYS SLMD600H10L or it's bigger brother
John I'm vanilla
John Haven;t used it
Shayna From @Shantam Raj : "In the aftermath of a nuclear war when there is no more infrastructure, do you think energy harvesting would come to our rescue? What type of energy would be exploited more than the others? How would the world of electronics adapt to such a situation?"
Richard Hogben anything similar that might be in stock?
John » Most electronics are not rated for heavy amounts of radition. Let's hope we do not have to design our circuits for this as well.
John Vault dweller you
Shayna Another from @Shantam Raj : "When you talk of load switches, would you rather prefer dedicated ics that need a power rail to function(thereby needing a specific minimum voltage to work) or a circuit made from mosfets in such a way that it can work even with really low voltages(say below 1V) and yet be able to switch properly? I spent a lot of time with the latter but failed miserably. Do you have such a switch design in mind or have you come across one ?"
John Minimum voltage is the key point of energy harvesting, Mosfet based switches works fine
John I don;t have a default design for you in mind but it is the way to go
John we also use dedicated ic's for switching sensors, but in cases where it is non critical or a softstart is required low power p-mosfets can be used
John ic's are designed to be as low voltage as possible but voltage doubler with low dropout diodes can be implement if you want to design it yourself
John might be interesting to look at
Shayna Returning to @Charlie Lindahl 's previous comments: "I'd still like to find a way to "energy harvest" for my Pebble and whatever my next watch is. The Pebble has a "port" for doing power and other interfaces, as does the Apple Watch"
John Pebble nor the Apple Watch were not designed with very low power in mind. Even the sleep current is higher than energy harvesting can provide.
Shayna Another person commented further: "Pebble nor the Apple Watch were not designed with very low power in mind. Even the sleep current is higher than energy harvesting can provide."
Shayna Or you rather :)
John Yeah liked that comment
John the problem is that you will have to step up the voltage high enough to charge the internal battery
John making it less efficient, but still go ahead, curious to see!
John mechanical design will be a challenge
John I suppose
Shayna "One big problem with charging LiPo batteries using solar energy harvesting or any other source of harvesting is that the charging is intermittent. For sometime it is charging and even when the capacity is NOT full, because of environmental conditions it may start discharging. But LiPos don't like this. They want to be charged and discharged properly and undergo this cycle for max longivity. So alternative storage elements need to be looked for, like supercaps. But the problem with supercaps is its linear discharge curve that digital electronics hate. Are there other types of storage elements apart from these two?"
Shantam Raj ...apart from these two that mitigate both the problems?
John Most of Ics have overvoltage under voltage protection saving your lipoBQ25504
John BQ25504 might be a good one?
George Hahn Oops, I forgot I'm not EST anymore :P
Josh Cole If I may ask, in that same problem space, Would you say super caps are better for energy harvesting devices, or lipo batteries?
John About the alternative storages,
Shantam Raj That is fine, even i am using BQ25505 and BQ25570 for my projects. But what worries me is that a charge cycle is never completed properly. This is detrimental to the LiPo.
John We love supercaps, but they do have their downsides
Christoph what about LiFePO4?
John We haven't used them, but could work
John more cycles = more better
John No problem at all
Shayna If you want to stick around for open discussion, we'd love that :)
John I;ll be here for some time, but won't be that long. If needed message me directly
kk.bedead wow, that's all right?
kk.bedead was not much of a use tho
Arsenijs Well, it's only as useful as questions asked
- I2C only consumes current when the pins are driven LOW. Every time the microcontroller communicates with I2C devices, it sends the address byte. Connecting the address pins to VDD instead of GND saves current every time you communicate with the ic.
- adding some bulk capacitance after the dc-dc converter reduces need for switching. Less switching = higher efficiency.
- increase 1kohm resistors at input of U1
- different schottky diode part numbers have different reverse current leakage
Arsenijs Thank you, John! Was a great read =)