EEVblog #1242 - Memory LCD+Supercaps+Low Power Design

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.

#SuperCap #LCD #LowPowerDesign

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[Boffin]

Does the display really need to be on ALL the time? Perhaps just a tiny micro that counts (in EEPROM) the startups and displays it when you press a button ?

[Afrotechmods]

Very cool! First I've heard of those SMD batteries!

[Stanton_High]

Pro tip, don't judge size by the picture on digikey. 😉

[isoguy.]

What you need Dave is a nucler surface mount battery, roughly 500, 000 years running a single smd led and pic

[dieSpinnt]

Thanks a lot for the video, Dave and that you let us participate in the highs and lows of development art :)
So you are designing a work-counter the hard way. The solar-road way:) Your premise that the counter has to show something all the time is so iron-proof that it over-complicates the design. In reality, such a device must operate at two points in time: when the data is collected (at power up) and when the data is requested or read.
A push button to request the value and counter storage in EEPROM after BOR with true power cutoff afterwards will give you the best possible results in terms of power usage.
The head is round so that the mind can change its direction: For such use cases electro-mechanical counters or work-hour-counters are used in the industry. They just use power when counting and display the data by design with no additional effort. You can rely on these devices, you do not break them and if, they still show the last value. Now I call them "electro-mechanical-ink display" for you IoT neewbs:P

[LaserFur]

The self discharge rate of the super caps and coin cells are quite high. I had to design a product that would keep the clock running for 10 years. I ended up with a rechargeable low loss battery. MS920T-FL27E 3V 6.5mAH

[ytrew]

I wish I could understand what you are talking about, but I'm always happy to hear that Bob's your uncle

[MysticalDork]

It's been mentioned before but I'll mention it again: You can get coin-format rechargeable cells. I've got a 1616 or similar sitting around here somewhere that came out of a solar watch. Much lower capacity than a primary lithium cell of the same size, but it is rechargeable/reusable.

[VeraTR]

Just put a mechanical counter (clicker) in it :)

[PorcineJim]

It looks like you are on the right track with the LCD with integrated controller. Previous comments about adding a solar cell to turn on the LCD only when light is available seem to be also right on. Take a look at PIC 12 series, 8 bits, 20nA in sleep. Wake on pin change, push the new value to the LCD, go back to sleep. You really have to be careful that your PCB is clean at these current levels.

[adamericsson]

I had a small digital wrist watch stay going under my bed for 10 years. Beeping every night at midnight. Never changed the battery

[gotj]

e-paper consumes LOTS of energy to update the image because you've got to charge some capacitors from nought to the relatively high +/- voltages it needs to move the e-ink capsules, then shut it down again the "high voltage" power supply until the next update (and in the process lose all the energy you put into the capacitors). The mere act of cycling on/off a "HV" power supply eats power, and that's in addition to the energy lost to migrate the eink capsules... IOW, epaper is only low-power when it's completely off, updating the image eats lots of power and energy too because it's not fast. For example, a clock that updated the only the minutes and not the seconds, can't be made to run on batteries (of a any reasonably small size) with an epaper.

[pigrew]

The self-discharge rate of super-caps is also fairly high. Perhaps a small rechargable lithium coin cell could work. Also note that current limiting is suggested for charging a super-capacitor (try not to design the circuit with only the diode as shown in the video).

[remotepeak]

There is other matter to care about. If device will not have at all backup supply, then between events which are counted, you need to store somewhere current status of counter. You will not read this from e-paper. So, is necessary i.e. external EEPROM or inside microcontroller EEPROM. Or even store it in part of flash memory. In any case, you must also pay attention to durability of such memory (write cycles).

[alecdacyczyn]

You're trying to reinvent the Electro-Mechanical Counter.

[NivagSwerdna]

Some muddled thinking here... firstly an I2C memory LCD is presented but later a discussion around uP with built in LCD drivers and a complaint that they aren't available in small packages... when using LCD direct you are going to need a fair number of pins since you need to connect all the segments/commons. I've used that PIC24FJ part in a weighing scales with always on clock display, it's a nice part.

[peteroneill]

PIC16LF1933, 8bit PIC with LCD driver, Sharp LCD still likely better solution.

[austfox]

Wow, I have been using CR2032 for years and it never occured to me they were 20mm in diameter x 3.2mm thick. Still learning something new everyday.

[michaelwilkes]

24:40. I think the self discharge of those avx super caps would be a serious problem. I think its pretty high if I remember.

[mrlithium]

Much better video than last one. very enlightening. learned a lot of new things.