low power microcontrollers, RTCs, ePaper and solar cells

[FrankBuss]

As a sub-project of my Nixie clock, I plan to use a battery backup real time clock (or gold cap backup). First I thought about the DS1307, but it needs 500 nA and the STM32L4 series claims 200 nA with RTC running. This makes me wonder, which CPU has the lowest power consumption?

In general the question doesn't make sense, because if no oscillator for the RTC runs, it is of no use for my application. Is there an industry benchmark to compare different microcontrollers better? Would be nice to compare the power consumption for different tasks, like implementing a real time clock with some given accuracy like 20 ppm from 0°C to 60°C (doesn't need an external watch crystal, if the microcontroller can do the accuracy internally) and wake up on some pin interrupt, and another task with wake up each second, and so on. The microcontroller manufacturers could implement and program their MCUs to solve the benchmark tasks, so that we can be sure that it is the best possible solution. Or someone like EEVblog could organize a challenge.

BTW, Microchip lists ATmega MCUs now, too for their XLP technology. Of course, they still use the old Atmel datasheets and nowhere in it is XLP mentioned. I love marketing

[TJ232]

The lowest power consumtion RTC that I ever used, PCF8523, 150 nA: http://www.nxp.com/products/signal-chain/real-time-clocks/ic-real-time-clocks-rtc/real-time-clock-rtc-and-calendar:PCF8523

UPDATE: found it, I was missing the bookmark, this one seems to be the one with the lowest power consumtion :
http://www.microcrystal.com/index.php/news/25-cat-news/cat-articles/186-x-treme-low-power-real-time-clock-module-from-micro-crystal

• 60 nA at VDD = 3.0 V in crystal mode
• 17 nA in calibrated RC mode
• Integrated 32.768 KHz quartz crystal

Sounds nice.

[brucehoult]

RV-1805-C3 and AM0805/AM0815 seem pretty similar.

RV-1805-C3  60 nA full crystal mode, 17 nA in "crystal calibrated RC" mode.

AM0805/AM0815 55 nA in full crystal mode, 22 nA  in "crystal calibrated RC" +/- 2 PPM mode, 14 nA in pure RC +/- 16 PPM mode.

[amyk]

The lowest power MCU would probably be one of those mask ROM 4-bit ones that can be found in various battery-powered electronics.

[FrankBuss]

Thanks, the ambiq micro devices looks good. The AM18X5 have even additional power management functions, like an 1 ohm switch, and a watchdog timer. And I like that it is available with a SPI interface. The microcrystal part has only I2C, which kind of defeats low power solutions, if you want low power when you read or write to it, too. Not a problem for my Nixie clock, but maybe I will use such a RTC for other projects as well.

But it was difficult to find a distributor who sells this chip. Future Electronics sells it in batches of 3,000. But the ambiq micro homepage lists Abracon as "RTC resellers". And looks like this is the same chip, it is just called AB1815 instead of AM1815: http://www.digikey.de/short/32d7pj

The 3x3 mm QFN-16 package is not easy to hand solder, but possible. Someone did already a breakout board for it:

https://lowpowerlab.com/forum/projects/ab18x5-breakout-board/

I think it should be combined with a gold cap like this:

https://www.digikey.de/short/32d7h2

The maximum allowed discharge current is 1 mA. Is this the same for the charging current? Then it could be charged in an hour and last for months (if the self discharge of the capacitor is very low).

[splin]

Well your original question was "what is the lowest power microcontroller" not an RTC. As far as I am aware, Ambiq's Apollo 1 ARM processor is the lowest at 35uA/MHz @ 3.3V when running Coremark, 419nA deep sleep mode with 32768Hz crystal - but good luck actually getting one.

But today, look what just popped into my email intray - a link to AMD's new ultra low power ARM M4F microcontroller

http://www.analog.com/en/products/processors-dsp/microcontrollers/ultra-low-power-microcontrollers/aducm4050.html#product-overview

Don't know how long it willl be before you can buy one but the specs are very promising - 40uA/MHz and 246nA in shutdown mode, RTC enabled. That compares to aound 110uA/MHz for the STM32L4.

Lets hope they can meet the target performance spec and don't decide to put a huge premium pricetag on it as it could be a real killer in the ultra low power battery powered sector.

[kwass]

Have you looked into the shelf life (battery self discharge) or leakage current (capacitor) for your backup power source.  Almost certainly these will be the limiting factors with an ultra-low power micro or clock chip.    With a CR2032 cell, for example, if your circuit draws less than around 3uA the 2032 shelf life will be the limiting factor -- 10 years or so.

[splin]

Have you looked into the shelf life (battery self discharge) or leakage current (capacitor) for your backup power source.  Almost certainly these will be the limiting factors with an ultra-low power micro or clock chip.    With a CR2032 cell, for example, if your circuit draws less than around 3uA the 2032 shelf life will be the limiting factor -- 10 years or so.

But he didn't say he was space limited. I tested an 11 year old Pansonic D cell which had been partially used in a torch sometime previously. At 82mA discharge it delivered nearly twelve amp hours and almost 15Wh which was very impressive given I don't know how much had been used previously.

This compares to the spec of 16Ah when new! However it has to be said that probably half the unused batteries from the same batch had leaked quite badly. These batteries were made in Japan and had been stored in a wardrobe so probably mostly at 10C to 15C; there's no guarantee that modern cells made in China would have such good self discharge performance.

The Energizer alkaline handbook shows a graph of self discharge of AA cells with 20% loss of capacity after 10 years @ 20C and only 5% loss after 14 years at 0C.

Leakage seems to be a much bigger problem than self discharge (in cooler climates at least) so if very long lifetime is required then perhaps a number of cells from different manufactures could be used in parallel using transistors/low drop diodes. The wires would be soldered/welded to the cells and the whole battery put in a plastic bag to contain any leakage.

[mikeselectricstuff]

If it's a nixie clock, it will be mains power, so the backup battery will only be used when power is lost, so power draw is not a big deal. A supercap may be a better solution for longest product lifetime

[hans]

Similar to Coremarks (which is set to compete with Dhrystone benchmark), EEMBC also has ULPBench:
http://www.eembc.org/ulpbench/

Ambiq micro's do very well. Unfortunately can't buy them from Farnell, and that's where the options end for me as a hobbyist.

To be honest quite amazed that Silicon Labs Energy Micro's EFM32 are not higher up the list. PIC24 XLP is mediocre at best apparently.

The list is quite shallow though. Testing low power stuff is quite hard to do right, and also quite touchy. I imagine they have certified hardware and tests before the allow a score onto the sheets, probably much harder than it is for a Coremarks benchmark.

I'm not sure what kind of test conditions are applied in this ULPBench. I have a feeling this test favours CPU heavy micro's, perhaps not important at all when your application is I/O limited and sleep heavy.

Also an often used trick to minimize power is use DC/DC's to bring down nominal 3V lithium batteries to the minimum voltage the chip can operate at - often 1.8V or perhaps lower. Just that can mean a jump from e.g. 100uA/MHz down to 60uA/MHz.

[Teuobk]

To the EFM32 comment: I've not found the EFM32 to be notably better than other Cortex-M solutions. In real-world testing, I've found the Nordic nRF52 or even some of the STM32F4s, for example, to often outperform an EFM32 Giant Gecko in terms of work done per microamp. Of course, your mileage may vary. That said, the EFM32 isn't bad, and I appreciate how SiLabs provides a decent free IDE (which not all vendors do).

[rsjsouza]

Have you looked into the shelf life (battery self discharge) or leakage current (capacitor) for your backup power source.  Almost certainly these will be the limiting factors with an ultra-low power micro or clock chip.    With a CR2032 cell, for example, if your circuit draws less than around 3uA the 2032 shelf life will be the limiting factor -- 10 years or so.

This is a critical factor. I have two MSP430 development kits that are complete watches powered by CR2032 batteries and they were turned on in 2004 and 2005 respectively and were never powered off through the t8me the batteries lasted: around 11 years on both kits. I imagine the shelf discharge was the main factor for this.

However, why use such low power in a nixie clock?

[FrankBuss]

However, why use such low power in a nixie clock?

Might be useful for other projects and with the Nixie clock I can test it.

[westfw]

It gets complicated, because really low-power microcontrollers tend to be designed to spend most of their time in very-low-power "standby modes", which vary pretty greatly in their utility (what is left running, what can cause wakeup, etc) and especially in how much time/power it takes to go from the standby mode to the operating mode...

I'd guess that most of the "very low power" microcontrollers laugh at battery-backup these days; power is low and batteries are good.  It's "energy harvesting" that is the new low-power target application - Can it meaningfully operate off of the uW of power available from stray RF, or Peltier harvesting of small thermal differences, or the occasional mechanical vibration...

[splin]

I've just seen this linked in danadak's post reporting Cypress's new PSOC6

http://www.eetimes.com/document.asp?doc_id=1331471

What is  particularly interesting is this bit:

Cypress' proprietary ultra-low-power 40-nm SONOS process technology enables the PSoC 6 MCU architecture to feature industry-leading power consumption with 22 µA/MHz and 15 µA/MHz of active power on the Cortex-M4 and Cortex-M0+ cores, respectively.

Seems a bit like waiting ages for a bus then 3 come at once! If those numbers are correct and directly comparable, it blows Ambiq and AMD's just announced ADuCM4050 out of the water in the low power stakes. And EFM32 and ST32L4 are left even further behind.

I wonder if ST have anything comparable in development as I guess they will have to respond?

[EDIT] I see Cypress already have a Cortex M0+ S6E1C1 (FM0+) uC which is specced at 40uA/MHz. I don't know about availability but the datasheet was revised in March 2016 so it looks like they have been around for some time. It seems I have managed to miss these previously.

[julianhigginson]

the silabs/energy micro parts really disappointed me a year and a half ago... at first they showed very promising low power mode specs, on the data sheet, (and I think three product page, too...) then the datasheet errata corrected those numbers and the power down mode was shown as basically double. you'd think that an error of 100% for advertised power consumption in low power modes on a product specifically marketed as low power would want to be communicated slightly more urgently than tucked away in an errata! I wonder if they've fixed that yet?

Sent from my A0001 using Tapatalk

[Dielectric]

What's interesting about the PSoC6, is that while the sleep and hibernate numbers are just OK (blame CMOS leakage at 40nm), those run currents are way down and it supports voltage scaling on the cores.  The design intent is more like an always-on but low-power mode so you don't have to sleep/wakeup constantly.

I'm actually curious about lifetime data on a coin cell, since they're notoriously bad at supplying surge current (tends to shorten their overall lifetime) but are better at supplying a low, constant current.

The S6E1xxxx parts are from the Spansion merger, they're pretty good but somewhat unknown outside of Japan and a little bit of Europe.  Tons of peripherals on them if you dig into the manuals.

[FrankBuss]

I created a breakout board with KiCad for the AB1815 RTC: https://oshpark.com/shared_projects/UJrkUq22

It is my first KiCad board, so I hope I've done everything right. Cost at OSH-Park is $2.25 for 3 boards and free shipping, if you chose USPS and I've shared the project, so everyone who wants one can buy it. But might be good to wait until I have tested it

This is how it looks like in the KiCad 3D viewer:



That's with version 4.0.6, which I compiled from source, in older versions it didn't look that nice.

Github repository with all KiCad files: https://github.com/FrankBuss/nixie-clock/tree/master/ab18x5-breakout

[theatrus]

the silabs/energy micro parts really disappointed me a year and a half ago... at first they showed very promising low power mode specs, on the data sheet, (and I think three product page, too...) then the datasheet errata corrected those numbers and the power down mode was shown as basically double. you'd think that an error of 100% for advertised power consumption in low power modes on a product specifically marketed as low power would want to be communicated slightly more urgently than tucked away in an errata! I wonder if they've fixed that yet?

Sent from my A0001 using Tapatalk

EM (and I guess SiLabs by extension) has had issues delivering advertised specs for years (remember the EFR24 radio? ). Their software libraries are excellent otherwise so its a major bummer. Their original Gecko series performed really well and was a game changer, but it looks like they're falling behind.

[ebclr]

This processor need only a few electrons to work

http://www.silabs.com/products/development-tools/mcu/32-bit/sim3l1xx-low-power-badger-board-evaluation-kit

[FrankBuss]

This processor need only a few electrons to work

http://www.silabs.com/products/development-tools/mcu/32-bit/sim3l1xx-low-power-badger-board-evaluation-kit

Well, the datasheet says 75 nA in power mode 8 (timers running, CPU in sleep mode). But this would be pretty good. But the PIC10F320 for example claims 20 nA, and looks like this is with a timer running, which can generate an interrupt to wake up the CPU.

[nctnico]

IMHO it is odd nobody mentions TI's MSP430 series which are supposed to be very low power. Usually the ultra low power modes have everything shutdown to a useless level so the numbers quoted in datasheets aren't worth the bits needed to store them. Especially when typical values are printed without a maximum. What counts is the power requirement to still do something usefull (like running a wake-up timer for periodic checks) and the time needed to wake-up. During wake-up a microcontroller draws power but doesn't do anything because the oscillators have not started properly yet.

[brucehoult]

IMHO it is odd nobody mentions TI's MSP430 series which are supposed to be very low power.

https://www.eevblog.com/forum/microcontrollers/lowest-power-microcontroller/msg1165011/#msg1165011

Well known as a pleasant low power pseudo-PDP11 [1] in these parts, I should think.

[1] 16 registers instead of 8, and corresponding fewer addressing modes to still fit in 16 bits. But otherwise...

[ebclr]

PIC10F320 is a crappy 8 bit, with only 512 Words of Flash Program Memory  64 Bytes Data Memory

Are you kidding?

SiM3L1xx

Up to 256 kB flash
Up to 32 kB RAM
Up to 62 GPIOs
50 MHz Cortex-M3 core
Integrated dc-dc converter
Variety of wake sources
128 or 160 segment LCD controller
Sensor interface
Hardware AES, CRC, encode/decode
Enhanced DMA with DTM
10-bit 1 Msps or 12-bit 250 ksps ADC
Current mode DAC
2 x SPI, UART and I²C
Analog comparators
Enhanced PCA, timers
Voltage reference and temperature sensor
Available in 40, 64, 80-pin packages

[brucehoult]

PIC10F320 is a crappy 8 bit, with only 512 Words of Flash Program Memory  64 Bytes Data Memory

Are you kidding?

So about 10x more data memory than required, and probably a lot more code space than required too.

SiM3L1xx

Up to 256 kB flash
Up to 32 kB RAM
Up to 62 GPIOs
50 MHz Cortex-M3 core

MASSIVE overkill. And 4x the power usage. For nothing useful in this application.

Great in other applications, for sure.

[tszaboo]

IMHO it is odd nobody mentions TI's MSP430 series which are supposed to be very low power.

From the top of my head, excluding the oddball 4 bitters, probably the MSP430 FRAM or the 0.9V parts will require the least power.

[GeorgeOfTheJungle]

Cypress' PSoC 4 (and perhaps 5?) also have low power modes with figures in the few-ish nano amps IIRC and the dev kits are cute and cheap:

http://www.cypress.com/documentation/development-kitsboards/psoc-4-cy8ckit-049-4xxx-prototyping-kits

[ebclr]

You can use only one fet transistor with few passives, this application does not need a microprocessor

[nctnico]

Cypress' PSoC 4 (and perhaps 5?) also have low power modes with figures in the few-ish nano amps IIRC and the dev kits are cute and cheap:

That may be but in many cases you'll need to read the fineprint and that will tell you a completely different story. Some microcontrollers can only come out of the lowest power state with a reset 

[GeorgeOfTheJungle]

Cypress' PSoC 4 (and perhaps 5?) also have low power modes with figures in the few-ish nano amps IIRC and the dev kits are cute and cheap:

That may be but in many cases you'll need to read the fineprint and that will tell you a completely different story. Some microcontrollers can only come out of the lowest power state with a reset 

Huh, right you are!

The PSoC® 4 provides five power modes, intended to minimize the average power consumption for a given application. The power modes, in the order of decreasing power consumption, are: ? Active ? Sleep ? Deep-Sleep ? Hibernate ? Stop

Active, Sleep, and Deep-Sleep are standard ARM-defined power modes, supported by the ARM CPUs and instruction set architecture (ISA). Hibernate and Stop modes are additional low-power modes supported by PSoC 4. These modes are entered from firmware similar to Deep-Sleep, but on wakeup, the CPU and all peripherals go through a reset.

Sleep modes are a few µA, only hibernate and stop are in the nano amps.

[FrankBuss]

You can use only one fet transistor with few passives, this application does not need a microprocessor

How do you build an RTC with one fet transistor with few passives?

[BrianHG]

You can use only one fet transistor with few passives, this application does not need a microprocessor

How do you build an RTC with one fet transistor with few passives?

I think 'ebclr' is thinking you only want a 32Khz oscillator.  Yes you can create a 32khz oscillator with a fet and watch crystal, but, feeding that to a MCU RTC clk input would probably draw the same or more than it's internal RTC all within the IC's die.
With 3 fets, you may be able to make a 1hz multivibrator oscillator, yes, this would draw less feeding the MCU RTC so slow, but, accuracy will suck and it may fail to oscillate.

'ebclr' may be also thinking of using an MCU in ultra deep sleep (which require reset to wake up), setting an IO to charge a cap and fet amp to wake up the CPU through reset a second later, or even 10 seconds later.  This 'might' work, but, once again, a RC 0.1Hz reset clock would suck in accuracy with temperature and system voltage.  But it would be functional.  I'm not sure how much power you would save though.  You will be using something like 20 mega-ohm resistors to charge and discharge the cap & bias the j-fet to get that nano-amp range.  PCB leakage, even a stray fingerprint, change in humidity anywhere near this would throw it out of wack, though, this solution will always run unless your MCU code crashes or forgets to cycle that cap before going to deep sleep.

The stand alone clock chips in the previous posts was the lowest power I've seen, second closely by using ultra low power MCUs running them at their absolute minimum possible VCC and at room temp.  Combining those dedicated clk chips with a MCU is such a close call in power consumption, I would just use the best possible MCU running it on it's own.

[GeorgeOfTheJungle]

This processor needs only a few electrons to work

That was funny, hahaha

[JPortici]

Cypress' PSoC 4 (and perhaps 5?) also have low power modes with figures in the few-ish nano amps IIRC and the dev kits are cute and cheap:

That may be but in many cases you'll need to read the fineprint and that will tell you a completely different story. Some microcontrollers can only come out of the lowest power state with a reset 

Huh, right you are!

The PSoC® 4 provides five power modes, intended to minimize the average power consumption for a given application. The power modes, in the order of decreasing power consumption, are: ? Active ? Sleep ? Deep-Sleep ? Hibernate ? Stop

Active, Sleep, and Deep-Sleep are standard ARM-defined power modes, supported by the ARM CPUs and instruction set architecture (ISA). Hibernate and Stop modes are additional low-power modes supported by PSoC 4. These modes are entered from firmware similar to Deep-Sleep, but on wakeup, the CPU and all peripherals go through a reset.

Sleep modes are a few µA, only hibernate and stop are in the nano amps.

also some deep sleep modes may remove power to RAM, erasing its content

[Bruce Abbott]

As a sub-project of my Nixie clock, I plan to use a battery backup real time clock (or gold cap backup). First I thought about the DS1307, but it needs 500 nA

And this is a problem because...?

[BrianHG]

As a sub-project of my Nixie clock, I plan to use a battery backup real time clock (or gold cap backup). First I thought about the DS1307, but it needs 500 nA

And this is a problem because...?

Maybe he wants to have a 10 year battery backup.
Or, to backup the clock with a 10000uf cap.

[Bruce Abbott]

DS1307 datasheet says:- "A lithium battery with 48mAh or greater will back up the DS1307 for more than 10 years in the absence of power at +25°C". CR2032 is 200mAh.

There seems to be an obsession with ultra-low standby current at present, people wanting >10 years life out of products that will probably be thrown away in 5 years or less.

Like the charger for my electric lawnmower, which had two CR1225's in series to back up the PIC16F616. The manufacturer came up with a clever way to extend their life - instead of connecting them to the MCU via a resistor, they used a capacitor! So the backup battery had heaps of life left when the charger malfunctioned due to a power glitch, and cooked the SLA battery it was charging. Result:- charger went in the trash after only 2 years...


     
 

[rsjsouza]

Like the charger for my electric lawnmower, which had two CR1225's in series to back up the PIC16F616. The manufacturer came up with a clever way to extend their life - instead of connecting them to the MCU via a resistor, they used a capacitor! So the backup battery had heaps of life left when the charger malfunctioned due to a power glitch, and cooked the SLA battery it was charging. Result:- charger went in the trash after only 2 years...

Wow... just... Wow.

[FrankBuss]

Maybe he wants to have a 10 year battery backup.
Or, to backup the clock with a 10000uf cap.

Yes, with a capacitor. And not important for the clock project, but can't be wrong to know the best possible device for a given task for other projects, like my solar cell powered ePaper project, if I want to add an RTC to it (the integrated RTC of the ESP32 I plan to use is not very accurate, I measured a few percent wrong per hour).

[BrianHG]

Ok, for a cheap capacitor at 22x the one I mentioned, 0.22F 2.5v here...
(2 Ohm, fast charge and discharge, small and cheap...)
https://www.digikey.com/product-detail/en/eaton/B0510-2R5224-R/283-2775-ND/1026743

After charging to 2.5v, with a MCU which draws 25ua at 2.5v and dies at 0.9v drawing 18ua (example approximate PIC XLP MCU with 32khz clock crystal), how long can you safely retain keep time?

However, with solar charging, I see why the absolute least is the best possible solution.

[GeorgeOfTheJungle]

my solar cell powered ePaper project, if I want to add an RTC to it (the integrated RTC of the ESP32 I plan to use is not very accurate, I measured a few percent wrong per hour).

Frank, perhaps you knew already, perhaps you didn't, just in case:

Those epaper displays are 0 power iff you leave them alone but updating the display is a (quite) power hungry operation. If you pretend to update the display say every minute (a clock) I'd swear that small PV is not going to be able to provide enough power. During an update, in a kindle 4, I see peaks in the hundreds of milliamps (@ the lipo) and the updates last at least 0,4s (in black and white mode, in grayscale it takes much longer!) if not more, up to 900ms. Part of that is due to the increased cpu activity, but most isn't, I think it has to do with the +/- 20V power supply that has to be turned on to update, charge some filter capacitors, do the update, then shut it down again and loose all the energy that went into charging them, repeat for every update cycle. That plus the work/power required to move the eink in the capsules as well, of course.

[FrankBuss]

The datasheet of the new ePaper display I plan to use says 8 mA, but I guess this is a bit low, or I read the wrong number. I've done some measurements with my 2.7" display and it was about 50 mA when updating, plus 20 mA for the 8266 module:



This will be more with the planned new ESP32 module, which needs 110 mA when running and transferring data over WiFi, and the bigger 4.2" display might need more power, too. But if it is less than 200 mA, it should be possible to update the display once per hour over the internet:

https://hackaday.io/project/20466-wifi-epaper/log/58513-solar-cell-tests-and-bigger-display

Maybe the RTC wouldn't make sense for the display then. But it could measure exactly how long it couldn't connect to the internet, if there is some problem

[GeorgeOfTheJungle]

Yes, once per hour requires 60x less energy than once per minute :-) But the updates in a larger display will also take longer => draw more energy. I love these eink displays. Can that one do grays or is it b&w only? I've seen there are new ones that can paint in red and black! How cool is that?

[GeorgeOfTheJungle]

I'm also having problems with the clock drifting too much while in sleep mode, I'm tempted to add a DS1307 for timekeeping.

[FrankBuss]

Can that one do grays or is it b&w only? I've seen there are new ones that can paint in red and black! How cool is that?

Yes, I'm planning to use one of those, it is this one:

http://www.pervasivedisplays.com/products/420

Click on the "Spectra (E4)" tab to see the technical details and for the right Digikey link, the other one is the black/white version. I have already one and when I bought it, there were like 10 in stock at Digikey, now 10 weeks lead time. My breakout board from OSH Park for testing it should arrive soon.

I think they have gray scale displays as well. But someone managed to display gray scale images on a black/white display, just with clever timing:

http://hackaday.com/2017/04/20/e-ink-display-driven-diy/

Maybe I can do this too with my display, the ESP32 should be fast enough.

[TJ232]

The datasheet of the new ePaper display I plan to use says 8 mA, but I guess this is a bit low, or I read the wrong number. I've done some measurements with my 2.7" display and it was about 50 mA when updating, plus 20 mA for the 8266 module:



This will be more with the planned new ESP32 module, which needs 110 mA when running and transferring data over WiFi, and the bigger 4.2" display might need more power, too. But if it is less than 200 mA, it should be possible to update the display once per hour over the internet:

https://hackaday.io/project/20466-wifi-epaper/log/58513-solar-cell-tests-and-bigger-display

Maybe the RTC wouldn't make sense for the display then. But it could measure exactly how long it couldn't connect to the internet, if there is some problem

"20 mA for the 8266 module" are you sure about that? I really have the feeling that you need way more for ESP8266 module. Like 200-250mA more at peak.

[FrankBuss]

Peak is 170 mA when sending and receiving over WiFi. When WiFi is disabled, the datasheet says 15 mA, so this looks plausible.

[TJ232]

Peak is 170 mA when sending and receiving over WiFi. When WiFi is disabled, the datasheet says 15 mA, so this looks plausible.

I am really looking forward to see a full ESP8266 boot process ending with no more than 15-20mA peak.

[GeorgeOfTheJungle]

Those red and black eink displays I'd bet come from http://www.good-display.com/ if so you can get them @ aliexpress too.

WRT the greys the kindle has several "waveforms" to choose from, the waveforms are the recipes (that come in a serial flash chip on the display itself) that tell the driver what voltage pulses to apply at a given ambient temp to get a given grey level in that particular display.

Another thing that will drain some energy is that every few update cycles you're going to have to redraw everything twice, first inverted then not to eliminate ghosting, so double the energy of a normal update.

We are lucky that you're the OP because this is going wayyy off topic hahaha.

Edit: add ghosting picture

[GeorgeOfTheJungle]

About those IXOLARTM solar cells, they are 0,089*0,055= 0,004895 m2 @ 22% efficiency @ 1 sun wouldn't that be 0,22*1000*0,004895= 1,0769 Watts ? Why do they say 22% and 714mW?

[FrankBuss]

About those IXOLARTM solar cells, they are 0,089*0,055= 0,004895 m2 @ 22% efficiency @ 1 sun wouldn't that be 0,22*1000*0,004895= 1,0769 Watts ? Why do they say 22% and 714mW?

Good catch. That's what the datasheet says. I guess it clips above certain lux.

[GeorgeOfTheJungle]

My kindles draw ~0,71 mA in sleep mode (memory on, data not lost), that's about 0,00071*3,7= 0,002627 W= 2.63 mW. That's a problem because I want them to run on batteries for a year or more, and @ 0,71mAh day and night during a year that's 0,71*24*365= 4515 mAh. Do you think that those tiny PVs could supply 2.63 mW on average *indoors*, perhaps? So that sleep time will cost me nothing in terms of battery life?

[FrankBuss]

My kindles draw ~0,71 mA in sleep mode (memory on data not lost), that's about 0,00071*3,7= 0,002627 W= 2.63 mW. That's a problem because I want them to run on batteries for a year or more, and @ 0,71mAh day and night during a year that's 0,71*24*365= 4515 mAh. Do you think that those tiny PVs could supply 2.63 mW on average *indoors*, perhaps? So that sleep time will cost me nothing in terms of battery life?

Yes, that's possible, see my log article:

https://hackaday.io/project/20466-wifi-epaper/log/58513-solar-cell-tests-and-bigger-display

I measured about 5 mW max with 200 lux, which really isn't very bright, and if you have some daylight during the day, it would be no problem at all. I guess you could stick the solar cells on the back. You could even use less efficient and cheaper cells, because there is more room on the back of the Kindle than I planned for my device.

But you would need to modify your power supply. With the LTC3106 I plan to use for my project, everything is done for you, like switching between a backup battery and the solar cells, and even charging the battery when enough solar power is available. I guess if you place it somewhere with lots of sunlight (maybe not in direct sunlight to avoid damage) you even would not need to charge it at all from mains anymore. Would be a nice hack for hackaday.io.

[GeorgeOfTheJungle]

Ok, thanks. I'm going to order a couple of those to check it out. I've added a picture of ghosting in a message above so you can see what my kindles do after a couple of hours without full screen updates, as I'm painting the time every minute, that's after about 120 screen updates. In my case a full update every hour (1 every 59) seems to work fine and fix the issue. But I suppose YMMV because your epaper surely won't behave exactly like these.

[FrankBuss]

I didn't check partial updates so far as for your clock, might be the same problem with my display. Maybe do a full black/white cycle for the rectangle area where the digits are painted.

I also noticed in the current firmware for my Pervasive Displays that their firmware changed the update process: they don't use the inverse version of the old image anymore, but the process is like this: inverse version of the new image, full black, full white (I can't test it with my old display, could be full white/full black as well), and finally the normal version of the new image. Maybe this helps, too.

[GeorgeOfTheJungle]

they don't use the inverse version of the old image anymore

What I do is paint the inverse of the *new* image then normal. Also it's very easy to do that directly on the pixelmap of the framebuffer. Works fine for me.

[FrankBuss]

Ok, maybe try the full black / full white for the rectangle area where the clock is before you paint the normal image, then the full display update should not be necessary every hour.

[splin]

About those IXOLARTM solar cells, they are 0,089*0,055= 0,004895 m2 @ 22% efficiency @ 1 sun wouldn't that be 0,22*1000*0,004895= 1,0769 Watts ? Why do they say 22% and 714mW?

Good catch. That's what the datasheet says. I guess it clips above certain lux.

Solar cells don't clip. Looks like another case of marketing bull*hit. According to the diagram the actual net, active area = 16 x 12mm x 20mm = 3840mm after you account for the strip round the edge and the tabbing. That makes the cell efficiency more like 18.5% at best. Not that that is important - the relevant number is 714mW @ 1000W/m^2

Unfortunately the spec has nothing to say about low light performance despite devoting a fair portion of the spec talking about indoor light levels. Curious that they bother to provide Voc plots against irradiance but not the more important Isc. It's hardly because they haven't done the tests after all.

I'm very surprised you managed to get 5mW indoors; I just measured some 45mm x 65mm polycrystalline panels indoors in artificial light - a single 13W, 1500 lumen LED bulb room light, with some light still coming through the window. Unfortunately I don't have a light meter. Placed on my desk with no shading, Voc = .37V, Isc = 70uA so power probably around .7 * .37 * 70 = 18uW. Scale that up to your panel (based on net area) would give 35uW!

Moving the panel 500mm horizontally and raising it 300mm so that it is approx 1m directly below the room light the output goes up to .62V, 190uA or approx 83uW. The efficiency of my panels is probably pretty poor but the disparity is still enormous. I don't consider this room to be badly lit but the illuminance is likely far lower than in a typical office.

I just tried another panel which I know performs fairly well; it believe it is monocrystalline but I'm not certain. That produces 81uW and 280uW (scaled) in the two positions. My point is that you may well get much less output in many home situations - I have a Casio solar calculator which is fine for office use but is hopeless at home as you have to hold it right up to a bulb for several seconds to get it to start up!

Another data point - the panel spec shows typical office illumination levels starting at 9W/m^2. That panel would produce around 6.4mW at 9W/m^2 assuming its output doesn't drop off at low levels (unlikely). That suggests your test was conducted at light levels more typical of an office. That may be pefect for your application but be aware that it probably wouldn't be useful in many home situations.

[EDIT] And be aware that there can be considerable differences in low light performance between different samples - eg. I tried another panel of the 45x65mm panels which produced less than half of the output of the first (but are similar in full sun). This may be less of an issue with high quality panels but is of course unspecified.

[GeorgeOfTheJungle]

Ok, maybe try the full black / full white for the rectangle area where the clock is before you paint the normal image, then the full display update should not be necessary every hour.

That costs "a lot" of energy... I have to account for a full year of updates!

[GeorgeOfTheJungle]

@splin I have hope that what @FrankBuss has measured will be about right. And as thousands of mAh are at stake... I want to believe!

[FrankBuss]

I have measured the 200 lux with this instrument, cheap but very useful for such measurements: http://cgi.ebay.de/182356676136
The light source are 3 halogen bulbs, 50 watt, 1.5 m distance and no light from outside (was evening). But the lux value looks like it is standard for normal home lighting:

http://worldofleds.co.uk/lux-levels.htm

Problem is, I measured it lying on my workbench, will be less when sticking on the fridge, as one of my application idea is. But even with 1 mW it should be possible to do an update once per hour, which is my goal.

I think there are big differences for the solar cells, not only the efficiency, but also what part of the spectrum can be used. My halogen bulbs are very yellowish, such warm light is typical for many home lights. Some solar cells are more optimized for the colder sun light spectrum. And look at the price for my solar cells, there has to be a reason that they are multiple times as expensive than some cheap polycrystalline cells from eBay

[splin]

I have measured the 200 lux with this instrument, cheap but very useful for such measurements: http://cgi.ebay.de/182356676136
The light source are 3 halogen bulbs, 50 watt, 1.5 m distance and no light from outside (was evening). But the lux value looks like it is standard for normal home lighting:

http://worldofleds.co.uk/lux-levels.htm

Agreed, but in many homes living areas may be more like 100 lux or less - depends on personal preferences.

Problem is, I measured it lying on my workbench, will be less when sticking on the fridge, as one of my application idea is. But even with 1 mW it should be possible to do an update once per hour, which is my goal.

I think there are big differences for the solar cells, not only the efficiency, but also what part of the spectrum can be used. My halogen bulbs are very yellowish, such warm light is typical for many home lights.

Ah-ha! You didn't provide that info in your blog. So....

Some solar cells are more optimized for the colder sun light spectrum.

I swapped the LED bulb for a 150W incandescent. Perhaps 2200 lumens so approx 45% more than the LED. The output of the first panel, on the desk, was now 541uW - approx 30x as much. Moving it to 1m below the bulb increased that to 1410uW or approx 17x LED bulb.

Scaled up to your panel that would be 1.05mW and 2.73mW. In the second case at 1m from the bulb lux = lumens/area = 2200 lumens / (4 x pi x r^2) = 175lux. 2.73mW/175*200 = 3.12mW. If your panel is 22% efficient that makes mine 13.7% which is about what I'd expect given their age and being cheap polycrystalline cells from eBay

So from this I think the conclusion is that you should expect *much* lower outputs with LED lighting at similar Lux levels - which you'd expect as they put out much less power in total. The colour temperature is almost irrelevant - a 100W incandescent bulb puts out 100W of energy, of which the panel is responsive to perhaps 35% of the spectrum - ie. visible light plus some of the near infra-red. That means a solar panel completely surrounding the bulb could receive up to 35W of light plus near infra-red.

An equivalent 13W LED bulb may lose 3W in the driver; of the remaining 10W the LEDs may be around 14% efficient so perhaps 1.4W would be available for the solar panel with rest being dissipated as low temperature heat which the panel can't utilise. 1.4W is 1/25 of the power aailable from the incandescent - which isn't far of what I observed notwithstanding the very crude experimental conditions and broad assumptions.

This is made worse by the severe drop off in efficiency of a solar cell, including monocrystalline, at low light levels. At 200 lux when provided by the sun or an incandescent bulb, the drop off may be minimal but 200 lux from an LED is a very much lower power level and the efficiency may well be much worse. I say *may* as the spectra are very different so more research is needed to be sure. Its easy to measure though using your panel of choice and a suitably LED lit room.


Some/many people may still use halogen bulbs in downlights, but lots have switched to LEDs and it's probably only a matter of time before they are banned altogether. Unfortunately I think you are going to have to rethink this project.

[FrankBuss]

Right, I noticed the same problem when trying to increase the power with my LED flashlight. It looked brighter and the lux meter showed a higher value, but the solar cell output power was actually lower. So it might only work if it is installed somewhere with enough daylight. And for better exposure maybe a construction like this would be a good idea:



Would make it more stable, too, instead of just relying on magnets.

[GeorgeOfTheJungle]

Thanks @splin, el aguafiestas