The best advice I’ve seen online (ok, it was ChatGPT) is that it’s just not worth it to work with such small amounts of electricity, because the equipment required is too expensive and sophisticated (e.g, devices to read the charge of a capacitor without discharging it) to make anything that’s efficient enough to be worthwhile.
I guess ChatGPT has never heard of passive RFID tags? LLMs have some good uses, but they’re not great at a lot of things. You can’t really advance science and engineering by strictly regurgitating scraped text.
There are reasons to grab small amount of electricity from the environment. Why have a battery in a pacemaker if you can generate power via mechanical forces? It really just depends on the use case on how practical and feasible it is.
Oh yeah, I hear you on LLMs. Technically, ChatGPT has not “heard” of anything. It’s generally something I use as a jumping-off point when I’m desperate and don’t know what search query to use.
Does passive RFID harvest its power? I don’t know much about RFID (I’ll probably head over to wikipedia after this comment) but I figured that it was a circuit that, when given a bit of energy from a reader, sends back an RF signal with an encoded ID and that in the absence of that powered reader, the RFID device wouldn’t be transmitting anything.
Yes, the circuit in an rfid device gets its power by harvesting energy from the RF source it’s being illuminated with. A smaller version of wireless power transmission first invented by Tesla (the person, not the car company). Similar principles were used in the Cold War for surreptitious listening devices. Neat tech.
The most basic RFID tags will just send back an ID. The complexity can shoot way up and have all sorts of integrated circuits, mostly around encryption.
I guess it’s more of a semantic argument at this point, but would you not consider a tiny computer (RFID tag) that powers itself solely off of radio waves not a form of energy harvesting?
I guess the difference for me would be how long it stores that energy for, but the difference is probably semantic and easily changed with a few capacitors.
I would say “energy harvesting” is when the receiver and transmitter are not designed to be used together and they are not physically close together. Otherwise your electric toothbrush and Qi charger might count.
That’s a good point. What about long range RFID skimmers? You could argue the tag wasn’t designed to work with a skimmer. I guess that’s more like energy injecting?
There’s actually a decent amount of research into exactly this sort of thing, called, appropriately, “energy harvesting”. Depending on the application, it can be fairly effective. I know that vibration energy harvesting has been successfully in machinery monitoring applications, for example. I haven’t looked much into stray EM harvesting, but I’m sure it is possible…most likely to supplement a primary energy source rather than as the main source itself. But, yeah, for sure it’s an interesting topic with a fairly good amount of study into it…I think the University of Michigan had a few good research programs related to harvesting for ultra low power applications. You night check out some of what they’ve done
ATTiny would definitely work. Ive use them for really really long timer systems with some trial and error.
You should maybe just look at a bigger battery depending on what lifetime you would expect? They are not exactly super low power(at least the ones I have used)
You could go with an DS1339 which is an RTC with two programmable time of day alarms. If you only need timing you might as well do that. But if electronics isn’t really your thing then just add a bigger battery for the attiny85, make sure to run it at it’s lowest clock speed.
I use the Attiny10 in this context. At 3.5V operation and using the Watchdog timer + deep sleep… that should cost you about 4.5 uA when the lamp is off. Then a bit more when it is on (about 40uA assuming whatever the GPIO is connected to is high impedance), as you have to enable the I/O clock (but most things and peripherals can stay off). So an average consumption of 10.4 uA, or 31 years of operation off two 1.5V cells – of course they’re not rated for this long and the actual light will consume far far more power. The point is that the current consumption of the system is absolutely dominated by the light-producing component, in other words the control system is highly efficient.
You can implement as a state machine, e.g. something vaguely like:
Set WDT to trigger an interrupt instead of the RESET vector. Then set WDT to trigger after 8s. Then on wake increment a register (you will need 2 registers, 8 bits isn’t enough). Compare these registers to constants that set the timer duration. On compare match, change the machine state.
Machine state 1: GPIO HIGH, timer duration 4h, I/O clock enabled. CPU sleep mode IDLE. Machine state 2: GPIO LOW, timer duration 20h, sleep mode POWER DOWN.
I think in assembly language but should be a similar process in C++. I’ve successfully implemented very similar (night-light timing) algorithms on this chip. I can’t give you power consumption metrics as none have ever run out of power over the past 6 months.
You could also use a crystal for the ATtiny and get the same accuracy as the RTC. It should be accurate to about 20-30 seconds per month with a good crystal.
The internal oscillator only has an accuracy of around 1% after you calibrate it. It would be off by over 7 hours after a month. It’s also quite sensitive to voltage and temperature changes.
You could try using the e-ink buddy from Adafruit. I bought one for driving a price tag e-ink as well but have not tested it yet unfortunately. On their site they say that e-ink connectors are pretty standardized.
no, this is fine, you can find it in routers all the time (usually with printed antennas, or wire antennas)
so it seems, however remember that at microwave frequencies you might start seeing distributed elements as a part of matching circuit (patches, open or shorted transmission lines etc) every fraction of mm is critical. i don’t know what impedance gets this thing on output, but it might be very well non-real. it’s usually done so that everything is matched to 50 ohms
assuming that output is matched to 50 ohm, which is usually the case, you can use any length of coax, as long as losses don’t kick in too badly. this means you also have to make your antenna 50 ohms. i see you’re using ceramic antenna, which provides matching circuit for you, but there are other options like inverted-F antenna (3cm long) or even smaller zigzagged *inverted F antenna or halo antennas (some 2cm dia), which would require matching. tradeoff is better efficiency (less heating; one of these antennas wastes almost 40% of power) and the fact that you can make them on your own
Thank you for your detailed reply, I really appreciate it. It answers my question and raises a whole bunch more :D, I think I need to brush up on general RF and get a better understanding of how it actually works. I shall do some youtubing and reading on it. I found a really good pdf that discussed antenna design but a lot of it I didn’t understand, so I’m going to need to learn a bit more.
if you want to measure anything rf, you’ll need a vector network analyzer like nanoVNA (some $40), this will be very useful in tuning/matching antennas (and making sure you won’t get reflections that could potentially damage transmitter if you screw up badly enough)
antenna design is usually limited by one of these things: size, gain/radiation pattern, efficiency, bandwidth (fixed here, entire 2.4ghz band)
you can probably use off the shelf antennas used for drones if these are small enough for your application
soldering coax can be tricky, don’t melt center insulation. you’ll need to size microstrip line so that it’ll have impedance 50 ohms as well www.pasternack.com/t-calculator-microstrip.aspx
However I would be interested to know where I can earn more abt the topic of electronics, I am very interested in learning it and it would be nice to get some guidance. ty in advance
I… Don’t actually know, I’ve just cobbled together information over the years. My dad worked in an electronics workshop but never taught me anything. There’s a good intro to electronics course on udemy and if you’re serious about it, try get the book The Art of Electronics, its like an electronics bible.
and on top of that, various amateur radio pages, some are indexed in dxzone.com
there seem to be two hard limits on antennas in general. one is for approx lossless antennas that are large compared to wavelength: gain, beamwidth and size are related through diffractive limit en.wikipedia.org/wiki/Diffraction-limited_system it’s really about capture area, which is intuitive for things like parabolic reflectors, but for things like yagi antennas there’s some defined capture area that ultimately depends on their length
the other one is on non-directional antennas that are small compared to wavelength. basically one good antenna that you can make is halfwave dipole, you can try various trickery to make it smaller, but this comes at a cost of either smaller bandwidth or increased losses, or both to lesser degree. it might make sense to make an antenna with 70% efficiency which is 3x smaller for example. it all depends on precise requirements
at the end of the day the most important material in any antenna are tradeoffs
Is this not the same ESP32 with an antenna? Although I don’t know how the nRF52840 from your question comes into play here. Don’t you normally use an ESP or an NRF, and not both at the same place (with the exception of a gateway maybe)?
The nRF was a useless inclusion tbh, sorry for the confusion. The nRF already has an smd antenna.
The thing with those antennas is the size of the antenna vs the size of the module, it’s almost twice the size, negating any benefit of having such a small module.
Hence my desire to use an SMD antenna on a small board instead.
So you have these boards already? Or could you just get other boards with an ESP32 and LiPo charger? Because many already have a printed or ceramic antenna built-in.
Do you know of others with charge controllers with that from factor? The only one close to it I’ve found is the is the m5stack m5stamp, but it doesn’t have a charge controller.
I don’t mind creating the daughter board, I think it could be fun.
We need a picture of the entire pcb. The ribbon cable (technically a flex pcb, not a ribbon cable) is totally custom and not something you can put a signal on. The little green pcb looks like the driver, so we would need pics of that and maybe figure out where you can input some kind of signal.
These kinds of displays can be really hard te re-use. Often their driver is just a simple blob (chip on board) which would be completely custom. This can be made cheaply to order with as few as 500 units. So mass produced readers often use completely custom stuff to get down to a really low price. Unfortunately this means it’s not possible te repurpose the screens later.
Spi is the norm for hobby displays because they are made to be driven easily. There is a driver chip that receives the spi signal and drives the display. With an actual product this often isn’t the case and the screen gets driven directly.
Hey, I am not 100% sure but from other screens i have seen it is probably to boost power. One of the open source ereaders has a little chip that is similure. It is probably a spi display. Do you have the model number of the panel?
I don’t have model number and there are zero indications to who manufactured it. I added a picture of the backside. That’s everything readable on the panel. Nothing else.
The connector on the PCB is called a ZIF (zero insertion force) connector. Normally they are specified by the number of pins, the pitch of the pins, and whether there is any locking feature or “ear” on the sides of the ribbon cable. It looks like a standard latching connector made by any number of companies.
The ribbon cable looks like it is custom designed for the display’s electrical pin out and the mechanical design of the enclosure.
If you can figure out the mfg of the display itself, you should be able to figure out the ribbon cable pinout.
I know a fair bit about connectors and circuit fab, but not an EE so hopefully this helps!
I added a picture of the panel, but as written in the other comment: no manufacturer to see - at least to me.
At least pin-count-wise, the driver I linked above should fit, and all e-ink displays for hobby use do seem to be driven by SPI, but whether it’s the “same kind” of SPI and pinout…
I ended up using spacers so that it does not come in contact with the metal box enclosure. Thanks for pointing out the mountijg holes. It was right there and I never noticed haha. I feel like an idiot.
Something weird happened... So I edited my comment: Ive used those exact relays, 3 in a single prototype that I was tinkering with quite a lot, so what worked best for me in the end was mounting a DIN rail into my enclosure (Any box would probably work for you? I needed IP65 so I used a proper box with glands for incoming wires.) And then the relay boards were hot glued to DIN rail mounts... (The relay boards are then lined perpendicular to the DIN rail) That ensured that I could add or remove the rails as needed.
The rest of my circuit is also mounted on another DIN rail... Also allowing me to swap out main boards as I programmed/ upgraded them with minimal effort.
This was all connected by DIY 'ribbon cable' so that plugging and unplugging was also a breeze..
Granted this all might be overkill for you? Ive also have had projects that still live in shoeboxes and they work but obviously it all depends on your use cases?
Just remember, if you go the box route, to make your life easier, make sure the box is big enough to work in if anything is to be mounted permanently. Its a massive headache trying to feed one wire past all the others into the hole if you are working 20mm from the edge of your box.
Hope this helps!
(Second edit):
I read like my arse... If youre installing inside the switchboard and already have din rails, then a rail mount would be the most convienient solution
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