• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 78 subscribers
  • Views 2753 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Lowest consumption LCD solution

Jeremy Hemmo
Prodigy 30 points
Other Parts Discussed in Thread: MSP430F6458

Hi,

I'm working on an application using a msp430f6458 and I'd like to add a LCD.

Power consumption is very important to me, and I need to display 4 characters (4*8-segments).
Those characters need to be displayed 24/7, and will almost never change (twice a day at most).
Obviously, I won't include a backlight.

I've searched for passive segmented LCDs online, but I couldn't find any with power consumption information (other than "low power"), and whether I need to refresh them (i.e. wake the microcontroller) often.

I would appreciate it if you could point me towards some suitable LCDs, and maybe help me understand how the LCD refresh process works, how much power it uses, and whether I need to wake the CPU.

Thanks a lot in advance,

Jeremy 

  • 0
    Guru 46710 points

    You shall read user manual first, http://www.ti.com/litv/pdf/slau208m

    chapter "32.1 LCD_B Controller Introduction".

    Also check datasheet, tables "Low-Power Mode Supply Currents (Into VCC) Excluding External Current" and

    "Low-Power Mode with LCD Supply Currents (Into VCC) Excluding External Current".

    Pay attention to fact that by tweaking LCD operation parameters you can get lower consumption.

  • 0 in reply to Ilmars
    TI__Genius 14715 points

    Jeremy,

    In addition, you may want to consider using an e-Paper / E-Ink type display for the ultimate in low power display capability.

    There are examples of driving these types of displays with MSP430 MCUs (they simply drive each 'segment' via each pin, rather than mux'ing like a higher-segment count display would).

    Anyway, just a thought.  A reference on our TI.com website is found here (in addition to others):

    http://www.ti.com/solution/electronic_shelf_label

    Enjoy,
    Chris

  • 0 in reply to Ilmars
    Prodigy 30 points

    Thank you very much for your helpful answer, llmars :-).

    If I may ask for a few more precisions, please:
    From what I understand, the tables give me the consumption without LCD load.
    How can I estimate the consumption with the load for a given LCD?
    And what type of LCD (static, n-mux) should I look into first, in order to achieve lowest consumption for 32 segments?

    Best regards,

    Jeremy

  • 0 in reply to Chris Yorkey
    Prodigy 30 points

    Hi Chris,

    I didn't think I could use an e-ink display directly, without a dedicated controller.
    Thanks for the input, I'll look into this solution too!

    Best regards,

    Jeremy 

  • 0 in reply to Jeremy Hemmo
    Guru 46710 points

    Jeremy Hemmo said:
    How can I estimate the consumption with the load for a given LCD?

    It's about display type, size, capacitances, leakages, update frequency, acceptable contrast level and maybe something else what's important for you but not others. I would rather order LCD sample and measure than even think of somehow estimating consumption using calculations.

  • 0 in reply to Ilmars
    Guru 117850 points

    Believe poster llmars has well covered lcd application.

    Long ago (beyond 15 years) our firm won a contract to produce, "Highly Visible, outdoor, 6"+ tall, 4-digit, 7 Segment Displays."  And - power consumption was important there, too.  This was for a large, famous, entertainment center in Los Angeles - we had 8 such displays to design/build/deliver.  Their purpose was to show the "starting time" of the next exhibit.

    Our solution (and we were in Lcd design/distribution bsns) was "Electro-Mechanical" 7 Segment Display - which required power only to Set/Reset any Segment.  Cannot remember the duration of Set/Rst strobe - but believe 100uS or so. 

    This center loved these displays - they had highly visible fluorescent segments - and contrast & viewing angle far beyond any Lcd...

    Such displays may still be offered today - in USA - commuter bus used these often.  (dot-matrix, though - today most have moved to Led)

    Noted your desire to put the MCU to "deep sleep" - I'm uncertain if or how the MCU can retain the Lcd display - in that condition.  (MSP not my area)  However - in the case for E-M display - there are zero power requirements upon the MCU - until the display is to be altered!  And - zero power requirements from such display - until change ordered. 

    Note that MSP did not have the visibility nor the lowered power consumption realized today (back then) - it was critical that our X brand MCU be able to "sleep" - as long as possible - to reduce power consumption.

    Quick/back of napkin calc. reveals (say 100uA total @ 3V - Lcd on-going demand.)  That's 300uJ per second - thus in 3,333 seconds (55.55 minutes) we've exhausted 1 Joule.  (J = Watt-Second)  Check me - "writing/calculating out loud here." 

    Scaled up to daily power usage - napkin shows 26.18 Joules/day as your power burden - and that "just" for the Lcd!  (should MCU be forced to remain on - or supply drive current to the Lcd - this power demand obviously increases.)

    Again this is quick/dirty - but may suggest that a twice per day change (if that) lasting for (32 segments * 100uS) = 3.2mS - may yield a reduced power burden.  Surely the segment coils will seek mA (likely 10's of mA) but the very short duration may justify.  (leave to you/others the "break-even" Power vs. On-Time calculations.)

    But - back of napkin enables 5V * 10mA * 100uS = 5uJ per EM Segment!  Now - should 50% of segments change - thats 5uJ * 16 = 80uJ.  Again - doing this quickly - but thus far - potential power savings appears to be 26.18 J / day (via Lcd) vs. 80uJ / day (via EM) display.  (EM assumes 5V @ 10 mA coil - driven for 100uS)

    Suggest that your search shift to a similar (require power only to change) technology {which is what E-Ink poster mentioned} - but which is free from the complex drive requirements of E-Ink - which you recognized...  If power savings dominates - direction here wins easily...

     

**Attention** This is a public forum