Author Topic: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design  (Read 2889 times)

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Online EEVblog

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EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« on: August 30, 2019, 01:51:11 am »
Part 2 of the power-up counter project, investigating the Sharp Memory LCD & custom LCD's + microcontroller (MSP430 + ST ARM + Microchip) low power design with supercaps, SMD ceramic batteries, and coin cells.

 
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Offline tineibous

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #1 on: August 30, 2019, 01:59:38 am »
Hey Dave, about the battery problem there's a solution if you want to use LCD's or more beefier MCU's but it's kinda overkill. The solution would be the use of betavoltaic batteries like this one from citylabs https://citylabs.net/products/
 

Offline johnlsenchak

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #2 on: August 30, 2019, 03:03:40 am »

Why not use  all three to power the  display ?, the micro-controller , along with the ceramic  super  cap  in  parallel   with the  battery ?
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Offline floobydust

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #3 on: August 30, 2019, 04:01:30 am »
I've always used primary lithium batteries for stuff like this, or alkaline if the costs must be very low and it doesn't operate much below freezing.

Tiny rechargeable lithium batteries like Seiko MS621FE are only rated 100 cycle life, 15-250uA self-discharge, not great. I see them used in car dashcam's GPS ephemeris.

I thought most of this device's energy used would be for (standard) LCD's high capacitance alternated constantly at 32Hz. Larger segments, more capacitance and energy used.
 

Offline chickenHeadKnob

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #4 on: August 30, 2019, 04:52:25 am »
whenever I run into  problems like this I step back and start from the ground up with the initial design criteria. You want to display power up cycles count without having the unit in question powered or even functioning.  OK.
 
Why not mount an SD/ microSD card connector on the product and generate a time stamped log file? That does require the technician to remove the card and read and display it on a phone or laptop, but then you can have a much richer detailed product health log. When not logging in normal operation the SD connector could be used for firmware update, based on a jumper setting.

Some youtube commemorators mentioned mechanical hardware counters. I believe I have seen completely mechanical types which are incremented via a lever-ratchet when the power switch is depressed.

Neither of these solutions would lead to interesting videos though, and like this type of video, where you explore speculative design paths.
 

Offline amspire

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #5 on: August 30, 2019, 05:19:02 am »
If you don't need high resolution for the visual display, you could look at making a display with a miniature stepping motor. You could make, say, a 0-100,000 hours dial or linear scale.

https://www.aliexpress.com/item/33055237658.html
https://www.aliexpress.com/item/33058354779.html

You could still have an alternate way of retrieving the accurate hours number from the microcontroller if you need it.

Will not need much power as you would only pulse the motor once in a blue moon. No power needed when the monitored device is off, so you do not need a special microcontroller.

Well under a dollar in cost, but you will need some custom hardware.
« Last Edit: August 30, 2019, 05:38:52 am by amspire »
 

Offline NickAmes

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #6 on: August 30, 2019, 06:17:24 am »
Building off of amspire's suggestion, a mechanical counter would be simple, rugged, and no-power. This unit seems suitable: https://www.ebay.com/itm/12V-6-digit-Mechanical-coin-meter-counter-for-arcade-operated-Vending-machine-TW/152798967527?epid=14013965374&hash=item23938736e7:g:Nz0AAOSw5dlaFkO-
 

Online jaromir

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #7 on: August 30, 2019, 07:22:26 am »
Quote
Not gonna get under 4uA with LCD

Just nitpicking: I did this https://hackaday.io/project/28550-light-level-geolocator with consumption of 2,5uA with LCD on. Perhaps I could do better if It wasn't few days before contest deadline.
Years ago I made thermometer with static (single backplane) LCD and somehow antiqued PIC16F917, it had average current consumption just under 2uA with LCD on. Powered by two AAA batteries that will never get electrically depleted within their lifetime.

On the other hand, it's not going to change anything on your components choice. I agree e-paper display would be better fit for that particular on/off counter application; if it was easily available.
« Last Edit: August 30, 2019, 09:10:35 am by jaromir »
 

Offline piranha32

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #8 on: August 30, 2019, 06:13:33 pm »
Dave,

won't Good Display sell you any of the 7-segment e-ink display they have in their catalog? http://www.e-paper-display.com/products_list/pmcId=22.html
Listed application is smart cards, and they look ideal for such a counter you're building.

Offline JustMeHere

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #9 on: August 30, 2019, 06:14:24 pm »
I found this E-Ink part on Digi-Key.  It is a replacement for the one in the first video.  I would love to know what type of chip can drive it though.  One pin per segment.  50 pins.

https://www.digikey.com/products/en?mpart=SCB721001&v=1272

Here's a bit of info on how to drive it (from the older part's listing):

https://media.digikey.com/pdf/Data%20Sheets/E%20Ink%20PDFs/SC005221_Dwg.pdf

Would this drive it (gotta love that price):

https://www.digikey.com/product-detail/en/cypress-semiconductor-corp/MB95F778MPMC2-G-SNE2/2015-MB95F778MPMC2-G-SNE2-ND/9644526
« Last Edit: August 30, 2019, 07:13:43 pm by JustMeHere »
 
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Offline SeanB

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #10 on: August 30, 2019, 06:54:34 pm »
One big thing about supercapacitors is the slow decay of voltage and also the slow rise of voltage when power is applied. Will your microcontroller, with or without a brownout reset, actually stop operation gracefully as the voltage drops, and, more importantly, many need a certain minimum power supply rise time to prevent internal race conditions that lock them up.

Your supercapacitor of say 1F has to be charged up, and via USB and some sort of current limiting, 100mA is the maximum current you can draw before the USB controller has to be powered up to negotiate a higher power consumption after enumeration. Though many ports will allow 500mA, most laptop chipsets do not. 30 seconds or so of power draw before the microcontroller powers up, if it does so at all with that slow a ramp, is not going to go down well. even worse some parts may stop running on voltage decay, while others keep on, so you might run into cases where say the slow clock keeps running, but the ALU has bits dropping out as the voltage decays, silently corrupting your stored data in RAM, or your EEPROM might only be able to get half an erase cycle done before dropping out, totally corrupting your stored data, and possibly erasing unwanted areas of the chip as well as the isolating transistors are not fully biased off.

You would have to add a series resistor to the supercapacitor to limit current, and a physical reset switch to short the power rails, to be able to recover from these deep discharge events, or even to allow first power up properly, but, so long as your application uses the supercap as just a "we will have no power for a short period" backup, like changing a regular larger battery, it will work
 

Offline billtodd

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #11 on: August 30, 2019, 07:33:31 pm »
Hi Dave ,
Just a follow on to the comment I made to the youtube video:

Here area couple of pictures of a self powered counter module that I re-purposed from a video recorder (ISTR but may have been something else)  This must be 25 years old and it is still working - date code on the 14093B  chip reads XKV949 , so 1994 (seems about right to me)

Turns out it is a 5 digit counter and seems happy counting at at least 1kHz.


If you want to take a closer look I could send it to you.

Bill
 

Offline Howardlong

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #12 on: August 30, 2019, 07:50:20 pm »
Not sure if you have seen my vid on running a large six digit always on LCD clock on a PiC, 1.8uA at 3v.

If I used a smaller LCD, and dropped it to four digit, I am confident it would run under a uA.



https://www.eevblog.com/forum/projects/happy-nerd-year

The trick is that as soon as you need LCD mid biasing, you might save pins but the current consumption goes up massively, an order of magnitude or so.
« Last Edit: August 30, 2019, 08:54:50 pm by Howardlong »
 
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Offline Kilrah

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #13 on: August 30, 2019, 08:04:23 pm »
won't Good Display sell you any of the 7-segment e-ink display they have in their catalog?
For sure but he doesn't like the bulky FPC interface as he said numerous times in the first video.

One big thing about supercapacitors is the slow decay of voltage and also the slow rise of voltage when power is applied. Will your microcontroller, with or without a brownout reset, actually stop operation gracefully as the voltage drops, and, more importantly, many need a certain minimum power supply rise time to prevent internal race conditions that lock them up.
Brownout reset is precisely there to avoid all of these issues. Micro is put in reset before the voltage drops below where funky things may happen, and only releases when a bit above that where again it's sure nothing funky can happen. Total non-issue.
 

Offline thm_w

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #14 on: August 30, 2019, 08:08:48 pm »
One big thing about supercapacitors is the slow decay of voltage and also the slow rise of voltage when power is applied. Will your microcontroller, with or without a brownout reset, actually stop operation gracefully as the voltage drops, and, more importantly, many need a certain minimum power supply rise time to prevent internal race conditions that lock them up.

Your supercapacitor of say 1F has to be charged up, and via USB and some sort of current limiting, 100mA is the maximum current you can draw before the USB controller has to be powered up to negotiate a higher power consumption after enumeration. Though many ports will allow 500mA, most laptop chipsets do not. 30 seconds or so of power draw before the microcontroller powers up, if it does so at all with that slow a ramp, is not going to go down well. even worse some parts may stop running on voltage decay, while others keep on, so you might run into cases where say the slow clock keeps running, but the ALU has bits dropping out as the voltage decays, silently corrupting your stored data in RAM, or your EEPROM might only be able to get half an erase cycle done before dropping out, totally corrupting your stored data, and possibly erasing unwanted areas of the chip as well as the isolating transistors are not fully biased off.

You would have to add a series resistor to the supercapacitor to limit current, and a physical reset switch to short the power rails, to be able to recover from these deep discharge events, or even to allow first power up properly, but, so long as your application uses the supercap as just a "we will have no power for a short period" backup, like changing a regular larger battery, it will work

Good points but from the video he's basically decided a small lithium cell is the way to go and a supercap that lasts long enough would be too large.
100mAh ~= 100F

I found this E-Ink part on Digi-Key.  It is a replacement for the one in the first video.  I would love to know what type of chip can drive it though.  One pin per segment.  50 pins.
https://www.digikey.com/products/en?mpart=SCB721001&v=1272

Here's a bit of info on how to drive it (from the older part's listing):
https://media.digikey.com/pdf/Data%20Sheets/E%20Ink%20PDFs/SC005221_Dwg.pdf

No voltage levels/timings mentioned though, but it could work with the 5V micro you mentioned.
« Last Edit: August 30, 2019, 08:12:42 pm by thm_w »
 

Offline piranha32

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #15 on: August 30, 2019, 08:23:16 pm »
won't Good Display sell you any of the 7-segment e-ink display they have in their catalog?
For sure but he doesn't like the bulky FPC interface as he said numerous times in the first video.

According to posted specs  GDEB0090A1-1 has SPI interface

Offline Kilrah

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #16 on: August 30, 2019, 08:53:20 pm »
Yes but it's physically large and impractical for the form factor he's after, again as he explained.
He wants the device no bigger than the display as much as possible and the bottom side has to be clean, there's no way you can fold that thing without making the whole board much bigger than needed.
 

Offline JustMeHere

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #17 on: August 30, 2019, 09:17:37 pm »
I found this E-Ink part on Digi-Key.  It is a replacement for the one in the first video.  I would love to know what type of chip can drive it though.  One pin per segment.  50 pins.
https://www.digikey.com/products/en?mpart=SCB721001&v=1272

Quote
Here's a bit of info on how to drive it (from the older part's listing):
https://media.digikey.com/pdf/Data%20Sheets/E%20Ink%20PDFs/SC005221_Dwg.pdf

No voltage levels/timings mentioned though, but it could work with the 5V micro you mentioned.

The in the original video Dave shows a PDF on how e-ink works: http://essentialscrap.com/eink/Driving_E_Ink_Displays.pdf
See page 18
 
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Offline thm_w

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #18 on: August 30, 2019, 09:47:09 pm »
The in the original video Dave shows a PDF on how e-ink works: http://essentialscrap.com/eink/Driving_E_Ink_Displays.pdf
See page 18

Thanks, so it looks like the downside of 5V drive voltage vs 15 is:
- Slightly reduced contrast (80%)
- Slower update rate (0.24s vs 0.7s)

So this is completely usable for this situation (low update rate).
 
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Offline GeorgeOfTheJungle

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #19 on: August 30, 2019, 10:40:27 pm »
epaper is only low power when it's disconnected... Just turning it on eats lots of energy (to #1 charge the caps in the +/- some tens of volts power supplies) and there's work needed to migrate the eink capsules too, and cpu time and work to do it too, and it's not fast (can't be, the eink capsules take some time to move). Then you shut it down again after the update to save power until the next update... and lose the energy you've put into the caps at step #1. Rinse and repeat, forever.
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Offline thm_w

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #20 on: August 30, 2019, 11:51:49 pm »
epaper is only low power when it's disconnected... Just turning it on eats lots of energy (to #1 charge the caps in the +/- some tens of volts power supplies) and there's work needed to migrate the eink capsules too, and cpu time and work to do it too, and it's not fast (can't be, the eink capsules take some time to move). Then you shut it down again after the update to save power until the next update... and lose the energy you've put into the caps at step #1. Rinse and repeat, forever.

I'm not sure what you are getting at, power consumption when active would be essentially non-critical, as you have a power source available. Hell half a watt or so would likely be OK.
The point is to keep that display visible *after* you unplug or switch off the product in question.

For a minimum turn on time, 2 seconds should be plenty no?
« Last Edit: August 30, 2019, 11:53:45 pm by thm_w »
 

Offline JustMeHere

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #21 on: August 31, 2019, 01:47:48 am »
The specs for the E Ink says .5ua per cm^2. The module is a shade over 2 cm^2.  So it draws at the most 3ua.
 

Offline nixfu

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #22 on: August 31, 2019, 02:49:38 am »
Seems like a graphical e-paper display would be the way to go even if a little more trouble to do characters, than a 7seg from the micro side. 
« Last Edit: August 31, 2019, 12:27:28 pm by nixfu »
 
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Offline GeorgeOfTheJungle

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #23 on: August 31, 2019, 10:32:36 am »
The specs for the E Ink says .5ua per cm^2. The module is a shade over 2 cm^2.  So it draws at the most 3ua.

LOL, the specs can say whatever, play with one and you'll see what I mean.
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Offline Howardlong

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #24 on: August 31, 2019, 02:52:36 pm »
The specs for the E Ink says .5ua per cm^2. The module is a shade over 2 cm^2.  So it draws at the most 3ua.

LOL, the specs can say whatever, play with one and you'll see what I mean.

I agree, that has been my experience with them too. While they do indeed draw no current when you’re not changing the display, it’s a completely different story when you do. You also seem to need to do a complete clean and refresh, at least on some units, as small areas that you change relatively frequently become “dirty” and the only way to correct for this is a complete refresh, expensive in terms of power.

For anything with dynamic content, such as a clock display, especially with a seconds display, they’re nowhere near as power frugal as driving a conventional raw LCD in my experience.
 

Offline RobertYates

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #25 on: August 31, 2019, 05:20:13 pm »
Just thought I'd chime in here to point out that what you're trying to create seems very similar to one of these modules.

https://www.hardlineproducts.com/product/hourtach-meter/

They have a very simple operation ( ie. they only count hours or show rpm ) and the lcd is always on, very similar to your cycle counter concept. It might be interesting to get one and tear it apart to see what they use to drive the LCD, though they are for use on outdoor equipment so they're probably fully potted.  :-\

Also note that there are other manufacturers of these style of engine hour meter, but I've actually used this one so I know for a fact that the LCD is always on.
 

Offline GeorgeOfTheJungle

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #26 on: August 31, 2019, 05:45:49 pm »
Specialists in low power ARM: https://www.silabs.com/products/development-tools/mcu/32-bit/efm32-zero-gecko-starter-kit

Quote
6.3 AEM accuracy and performance
The Advanced Energy Monitor is capable of measuring currents in the range of 0.1uA to 50mA. For currents above 250uA, the AEM is accurate within 0.1mA. When measuring currents below 250uA, the accuracy increases to 1uA. Even though the absolute accuracy is 1uA in the sub 250uA range, the AEM is able to detect changes in the current consumption as small as 100nA. The AEM produces 6250 current samples per second.

Quote
1.2 Features
• EFM32ZG222F32 MCU with 32KB Flash and 4K BRAM.
• Advanced Energy Monitoring system for precise current tracking.
• Integrated SEGGER J-Link USB debugger/emulator with debug out functionality.
• 20 pin expansion header.
• Breakout pads for easy access to I/O pins.
• Power sources include USB and CR2032 battery.
• 2 user buttons, 2 user LEDs
• 2 capacitve touch pads
• Ultra low power 128x128 pixel Memory-LCD
• Crystals for LFXO and HFXO:32.768 kHz and 24.000 MHz.
« Last Edit: August 31, 2019, 05:51:50 pm by GeorgeOfTheJungle »
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Offline Howardlong

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #27 on: August 31, 2019, 06:03:36 pm »
Specialists in low power ARM: https://www.silabs.com/products/development-tools/mcu/32-bit/efm32-zero-gecko-starter-kit

Quote
6.3 AEM accuracy and performance
The Advanced Energy Monitor is capable of measuring currents in the range of 0.1uA to 50mA. For currents above 250uA, the AEM is accurate within 0.1mA. When measuring currents below 250uA, the accuracy increases to 1uA. Even though the absolute accuracy is 1uA in the sub 250uA range, the AEM is able to detect changes in the current consumption as small as 100nA. The AEM produces 6250 current samples per second.

Quote
1.2 Features
• EFM32ZG222F32 MCU with 32KB Flash and 4K BRAM.
• Advanced Energy Monitoring system for precise current tracking.
• Integrated SEGGER J-Link USB debugger/emulator with debug out functionality.
• 20 pin expansion header.
• Breakout pads for easy access to I/O pins.
• Power sources include USB and CR2032 battery.
• 2 user buttons, 2 user LEDs
• 2 capacitve touch pads
• Ultra low power 128x128 pixel Memory-LCD
• Crystals for LFXO and HFXO:32.768 kHz and 24.000 MHz.

Silabs and their Gecko series have good marketing. In practice, I haven't found them particularly good compared to some other options.

Cortex M0, being 32 bit, is quite a tax in power terms despite what perceptions may be.

The devil is in the detail.
 

Offline Fungus

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #28 on: August 31, 2019, 09:36:42 pm »
I agree, that has been my experience with them too. While they do indeed draw no current when you’re not changing the display, it’s a completely different story when you do. You also seem to need to do a complete clean and refresh, at least on some units, as small areas that you change relatively frequently become “dirty” and the only way to correct for this is a complete refresh, expensive in terms of power.

I've read a few datasheets and they say things like the display can become permanently dirty if you don't do complete refreshes every few updates.

Also that direct sunlight will destroy them, and lots of other scary things.

If there's an LCD that maintains the display with no external signals and only draws 2uA then that seems the way to go.
 

Offline Kilrah

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #29 on: September 01, 2019, 08:28:55 am »
Also while e-ink will "retain an image forever" without power, the image may degrade over time.
Might be more pronounced with the "3-color" ones, but I bought one of those white/black/red ones and it likely sat for a couple of years on a shelf with the B/W company logo on, and it got all tainted red over time. So it'll likely still be readable, but contrast may reduce.
 

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Online mariush

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #31 on: September 01, 2019, 09:53:13 pm »
could go with a plain solar cell... https://www.digikey.com/product-detail/en/ixys/KXOB25-01X8F/KXOB25-01X8F-ND/9990432
high efficiency ... the room light alone should be enough for a few hundred uA...if you need to see lcd screen you have enough light to power it.
cheaper cells exist
store counter in eeprom in micro..  could use a 6-8 pin micro and separate lcd driver ic

if you can live with 1999 display, dt830 multimeters are 0.5$ in volume ...pull lcd and zebra strip out. job done.
« Last Edit: September 01, 2019, 09:55:54 pm by mariush »
 

Offline Howardlong

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #32 on: September 01, 2019, 10:00:21 pm »
could go with a plain solar cell... https://www.digikey.com/product-detail/en/ixys/KXOB25-01X8F/KXOB25-01X8F-ND/9990432
high efficiency ... the room light alone should be enough for a few hundred uA...if you need to see lcd screen you have enough light to power it.
cheaper cells exist
store counter in eeprom in micro..  could use a 6-8 pin micro and separate lcd driver ic


I have a few of these in a couple of different specs. I’ll be straight up with you about them, they’re disappointing in normal inside room lighting. If I get chance I’ll redo some tests and share.
 

Offline Kilrah

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #33 on: September 01, 2019, 10:01:21 pm »
Would expect the device to be enclosed in a dark cabinet and only viewed by an engineer allowed to open the panels when troubleshooting. No reason to think it would get any light.
 

Offline JustMeHere

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #34 on: September 02, 2019, 12:54:02 am »
The specs for the E Ink says .5ua per cm^2. The module is a shade over 2 cm^2.  So it draws at the most 3ua.

LOL, the specs can say whatever, play with one and you'll see what I mean.

LOL, this project is supposed to change once per power cycle.
 

Offline chickenHeadKnob

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #35 on: September 02, 2019, 01:57:06 am »
Would expect the device to be enclosed in a dark cabinet and only viewed by an engineer allowed to open the panels when troubleshooting. No reason to think it would get any light.
Doesn't need to, power cycle count is in eeprom. When the cabinet is opened the low power micro and LCD wakes up. I like this idea. I noticed my 37 year old sharp solar calculator now has dead batteries and doesn't work at all with moderate interior natural light however it works fine with high LCD contrast when illuminated with LED lighting.
 

Offline Kilrah

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #36 on: September 02, 2019, 10:47:17 am »
Indeed, that works
 

Offline NANDBlog

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #37 on: September 02, 2019, 11:22:31 am »
There is a product here, which has a 3.5 Digit memory LCD driven by an NXP low power LCD driver chip and a micro. The power consumption is about 5-10uA @ 3.3V (it is on a LiSOCl2 cell). Although it is a much bigger screen than what you have, the power consumption is easily the larger than what it comes from the datasheet. Although it is funny, when you disconnect the power source, it keeps on being visible for like 30 seconds with just the small capacitors on the board.
But selecting an off the shelf LCD and designing a project around it is mayor pain in the ass, so I would reconsider it with a button, or just blast the result through an UART every minute or something.
 

Offline Howardlong

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #38 on: September 06, 2019, 09:38:07 am »
Yesterday I did some evaluation testing with a few devices, notably PIC16LF1904, PIC16LF1934 and PIC16LF19175 that are largely pin for pin compatible drop in devices. 1ku pricing is $1.18, $1.46 and $1.19 respectively. All are available in 40 pin 5x5mm UQFN, but I used the DIP variants for this.

The best I managed so far at 3V with the display operating but with the CPU in sleep is on a PIC16LF1904, at 410nA plus 14nA per on-segment with the display attached, in static mode. This was using the internal LF oscillator, but no RTC functionality (I don't believe an RTC is a requirement in this case).

Measurements are taken with a Keithley 238 SMU and triaxial cable assemblies to the DUT. The MCUs were on solderless breadboard, and the debugger and any other probing removed. The LCD is DE 117-RS-20/7.5 soldered on a breakout board that had been cleaned in an ultrasonic cleaner.

As usual, you should never trust the datasheet when it comes to low power current draw specs: sometimes it's better, sometimes it's worse, and often the difference is dramatic. Judging by the quality of the quoted figures, I strongly suspect they use unsupervised interns on this work. Measuring sub-uA takes care and attention.

I found some interesting facets regarding the sleep currents. Sleep currents are important because they can be a show stopper before you've turned on a single LCD segment.

The typical sleep current for the PIC16LF1904 is listed as 160nA @ 3V, I was measuring only 17nA. The same applied to the PIC16LF1934 where the datasheet quotes 80nA @ 3V, and I achieved 16nA right off the bat. It's times like this you question your own measurement skills. Replacing the PIC with a 10Mohm resistor gave expected results, allaying any fears of a gross operator error.

On the other side of the coin, the PIC16LF19175 (a recommended replacement for the PIC16LF1934) measured 275nA at 1.8V, but at 3V it was a very different story, with in excess of 3uA (spec says 350nA). It's not clear to me why this is, but after spending half an hour tweaking I put it to one side, and concentrated on the PIC16LF1904, and getting the LCD operating.
 
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Offline Kilrah

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #39 on: September 07, 2019, 07:23:48 am »
As usual, you should never trust the datasheet when it comes to low power current draw specs: sometimes it's better, sometimes it's worse, and often the difference is dramatic.

The typical sleep current for the PIC16LF1904 is listed as 160nA @ 3V, I was measuring only 17nA. The same applied to the PIC16LF1934 where the datasheet quotes 80nA @ 3V, and I achieved 16nA right off the bat.
Well your unit used 17nA but one from the next batch may use what the datasheet says, so you still need to expect and design for the worst case in datasheet figures to still result in a product working to the expected spec. You'll maybe (or rather likely) get lucky, but it would be annoying to expect to get lucky and get bitten manufacturing 1000 units and that reel of chips happens to be on the datasheet's max values...
 

Offline GeorgeOfTheJungle

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #40 on: September 07, 2019, 10:25:42 am »
The best I managed so far at 3V with the display operating but with the CPU in sleep is on a PIC16LF1904, at 410nA plus 14nA per on-segment with the display attached, in static mode. This was using the internal LF oscillator, but no RTC functionality (I don't believe an RTC is a requirement in this case).

500nA@3V => 0.5e-6*3*24*365= 13 mWh/year
CR2032: 3V, 210mAh => 3*0.21= 630mWh

630/13 => would last 48 years in sleep mode, winner winner chicken dinner.

Now you only need to know the number of wakeup events per year, its runtime and its current :-) here's a spreadsheet:

https://docs.google.com/spreadsheets/d/1EC3Hb3dN89zZMW7C1lywiCgIFoLlzzcPUFokGHGDei4/edit?usp=sharing

#include <unistd.h>
int main (void) { while (!NULL) fork(); }
 

Offline Fungus

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #41 on: September 07, 2019, 10:29:33 am »
500nA@3V => 0.5e-6*3*24*365= 13 mWh/year
CR2032: 3V, 210mAh => 3*0.21= 630mWh

630/13 => would last 48 years in sleep mode, winner winner chicken dinner.

No need to argue over nanoamps. Once you get down into the single-digit microamp range, the battery's self-discharge starts to dominate.

Now you only need to know the number of wakeup events per year, its runtime and its current :-)

Yep.
 

Offline Rerouter

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #42 on: September 07, 2019, 10:32:24 am »
don't forget to check the leakage current for any ceramic capacitors on your device, larger value ones can be really leaky, e.g. a 47uF cap can be 500nA,

Also the battery self discharge, its not much, but it exists
« Last Edit: September 07, 2019, 10:35:48 am by Rerouter »
 

Offline GeorgeOfTheJungle

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #43 on: September 07, 2019, 10:51:41 am »
Howardlong, Silicon Labs have also got eight bitters, look : https://www.silabs.com/products/mcu/battery-operation (scroll down!)

« Last Edit: September 07, 2019, 12:58:18 pm by GeorgeOfTheJungle »
#include <unistd.h>
int main (void) { while (!NULL) fork(); }
 

Offline Fungus

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #44 on: September 07, 2019, 04:00:44 pm »
Howardlong, Silicon Labs have also got eight bitters, look : https://www.silabs.com/products/mcu/battery-operation (scroll down!)

Finding low power CPUs is easy, the problem is that Dave wanted one with LCD controller.

OTOH he has an LCD that can refresh all by itself so it's not really needed.

Me? I'd use a Tiny85 for this because it's what I know. It's an 8-pin chip so it's easy to work with and I've built stuff that runs for years on a coin cell using them. One gadget I built with a Tiny85 has been running continuously since March 2013 (using a 2540 cell, not a 2032) despite using the watchdog timer to wake up every 2 seconds to check a sensor.

The Mega328 used in Arduinos has a similar power consumption to the Tiny85 but a lot more pins. If I needed more pins I'd use one of those (probably a $2 Arduino Pro Mini with some components removed from the PCB to leave the bare chip).

If you know PIC or ARM or whatever? Use that instead.
« Last Edit: September 07, 2019, 04:10:58 pm by Fungus »
 

Offline Howardlong

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #45 on: September 07, 2019, 11:12:18 pm »
Here's my response video.



Code attached.

« Last Edit: September 07, 2019, 11:21:13 pm by Howardlong »
 
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Offline GeorgeOfTheJungle

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #46 on: September 08, 2019, 10:40:57 am »
Well done Howardlong, hats off to you !  :-+ :clap:

This padauk PMS154C may work for this? It's got an LCD driver.

https://lcsc.com/product-detail/PADAUK_PADAUK-Tech-PMS154C-S14_C168683.html

It's only 9 cents.

It doesn't seem to have flash/eeprom/NVRAM but, it isn't a must, is it? Unless you want to keep the count with no battery. And a quick battery swap doesn't necessarily mean a reset nor data loss, does it?

I can't read chinese (the datasheet) so I don't know for sure if it's got suitable low power sleep or wake up from sleep modes, but surely it does.
#include <unistd.h>
int main (void) { while (!NULL) fork(); }
 

Online mariush

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #47 on: September 08, 2019, 12:31:35 pm »
There's also lcd drivers that can be bought separately.
For example 30 cents for Holtek HT1621B :
soic https://lcsc.com/product-detail/LCD-Drivers_HT1621B_C7873.html
lqfp https://lcsc.com/product-detail/LCD-Drivers_HT1621B_C7532.html

or probably same chip, titan micro 1621, 15-20 cents in volume https://datasheet.lcsc.com/szlcsc/Shenzhen-Titan-Micro-Elec-TM1621_C41326.pdf

32 segments and 4 commons, min 2.4v , ~ 1mA at 3v
 

Online nctnico

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #48 on: September 08, 2019, 06:22:53 pm »
As usual, you should never trust the datasheet when it comes to low power current draw specs: sometimes it's better, sometimes it's worse, and often the difference is dramatic.

The typical sleep current for the PIC16LF1904 is listed as 160nA @ 3V, I was measuring only 17nA. The same applied to the PIC16LF1934 where the datasheet quotes 80nA @ 3V, and I achieved 16nA right off the bat.
Well your unit used 17nA but one from the next batch may use what the datasheet says, so you still need to expect and design for the worst case in datasheet figures to still result in a product working to the expected spec. You'll maybe (or rather likely) get lucky, but it would be annoying to expect to get lucky and get bitten manufacturing 1000 units and that reel of chips happens to be on the datasheet's max values...
I agree. The numbers from the datasheet should be used for anything that needs to go in production. The current consumption likely goes up with temperature as well so that is another factor.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Fungus

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #49 on: September 08, 2019, 07:30:32 pm »
The current consumption likely goes up with temperature as well so that is another factor.

Sure, but not by an order of magnitude.

I imagine the datasheet was written for the first production samples and they've improved the process since then without changing the datasheet (in case there's any batches of old chips in a warehouse somewhere).
 

Online nctnico

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #50 on: September 08, 2019, 07:52:48 pm »
The current consumption likely goes up with temperature as well so that is another factor.
Sure, but not by an order of magnitude.

I imagine the datasheet was written for the first production samples and they've improved the process since then without changing the datasheet (in case there's any batches of old chips in a warehouse somewhere).
Total nonsense. You can't ignore the numbers in the datasheet. Actually; these may even be too optimistic. In a large batch you may find devices which barely meet their specifications. Remember that chips are made using a lithographic process which has inherent errors. The datasheet reflects the margins of these errors. It is foolish to believe manufacturers are putting wider margins in their datasheets than absolutely necessary.
« Last Edit: September 08, 2019, 07:54:37 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Fungus

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #51 on: September 09, 2019, 01:58:57 am »
I imagine the datasheet was written for the first production samples and they've improved the process since then without changing the datasheet (in case there's any batches of old chips in a warehouse somewhere).
Total nonsense. You can't ignore the numbers in the datasheet.

I never said you could.

(At least: Not unless it's a small production run and you hand-select and test the individual chips  :) )
 

Offline Howardlong

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Re: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design
« Reply #52 on: September 09, 2019, 12:59:15 pm »
As usual, you should never trust the datasheet when it comes to low power current draw specs: sometimes it's better, sometimes it's worse, and often the difference is dramatic.

The typical sleep current for the PIC16LF1904 is listed as 160nA @ 3V, I was measuring only 17nA. The same applied to the PIC16LF1934 where the datasheet quotes 80nA @ 3V, and I achieved 16nA right off the bat.
Well your unit used 17nA but one from the next batch may use what the datasheet says, so you still need to expect and design for the worst case in datasheet figures to still result in a product working to the expected spec. You'll maybe (or rather likely) get lucky, but it would be annoying to expect to get lucky and get bitten manufacturing 1000 units and that reel of chips happens to be on the datasheet's max values...
I agree. The numbers from the datasheet should be used for anything that needs to go in production. The current consumption likely goes up with temperature as well so that is another factor.

In general, I agree, but I'll caveat that with a couple of things if I may.

Firstly, this is making the assumption that the figures you require for your use case are there in the data sheet. For example, LCD static mode consumption just doesn't appear in most PIC data sheets that have an LCD controller, but they do sometimes include some figures for the multiplexed modes that require power hungry charge pumps and bias networks. Worse still, even from the same manufacturer, it's often difficult to compare like with like, because consumption figures aren't specified under the same criteria. Sometimes you will just have to characterise those figures yourself.

Secondly, in most circumstances I'd agree that the datasheet (and any errata) should be the go-to place for definitive figures. Doing things like ignoring timing limitations and sticking 5V on a non 5V-tolerant pin is asking for trouble. Specifications such as current consumption are often specified as "typical" and it's very rare, if ever, to see a distribution. Sometimes there is a maximum quoted for a given temperature and Vdd: whether you choose to use this or not is more subjective, and depends on the context and project requirements. Irrespective, you'd be nuts not to measure and characterise yourself. Yes, temperature is a big delta on static current and needs to be taken into account based on the project requirements. It's not even uncommon to see disclaimers on datasheets on current consumpmtion figures like "These parameters are for design guidance only and are not tested". In such circumstances, your only option is to characterise these figures as best you can yourself.

In particular, in my experience of Microchip parts, which is where by far most of my experience lies, I find quoted current consumption specifications at the low end are sometimes significantly different to those specified. Sometimes it's worse, sometimes it's better. Sometimes they're spot on. Sometimes the figures are just so out of kilter, you know something's not right. It's not uncommon to spend hours trying to work out what tweak I need to make to get the quoted figures, and sometimes it just doesn't work out.

FWIW, the sub 20nA@3V for PIC16LF1xxx devices in "all-off" sleep mode is quite common (although note, it's not universal) across the range IME (e.g., see https://www.eevblog.com/forum/microcontrollers/pic-power-consumption/msg2113987/#msg2113987). Keep in mind that ultra low power on PICs is one of my "skills" shall we say, I have a fair bit of experience across the range, but equally it's a big subject with plenty of detail and nuance, and I accept you can never have never enough experience.

What I can say is that I encountered similar measurements on PIC16LF1906 and '1907 devices, the same family, but likely from different batches and wafers. The same applied to the '193x family. Not a great sample, I agree, but enough for me to be confident that I didn't just get lucky. For the '1917x series, where claimed sleep figures at 3V were miles out, I only tried two devices, almost certainly from the same batch, but also something with the way there was a dramatic increase in current as I turned up the volume from 1.8V to 3.0V. The jury's still out on that one, it could easily be an operator error!
 


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