Author Topic: EEVblog #1242 - Memory LCD+Supercaps+Low Power Design  (Read 3093 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-
 

Offline 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.
 


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