STM32 and 7 segments LCD driving ?

[asterix]

Posted on June 29, 2008 at 14:34

STM32 and 7 segments LCD driving ?

[asterix]

Posted on May 17, 2011 at 12:37

Hi,

I would like to control directly from a STM32 TQFP 48 pins , a 7 segments LCD (4 COMs, 32 Segments, 1/2 Bias), Do you know how to do it ? This is for pedometer. Thank you. Regards, Asterix.

[obtronix]

Posted on May 17, 2011 at 12:37

See

http://www.st.com/stonline/products/literature/an/6292.pdf note, I don't think the STM32 is really designed to drive the LCD continuously off a small battery that might be in a pedometer (coin cell?) It really doesn't have an appropriate low power mode, you have to run it in it's active mode (I think). So you will have to turn it off most of the time to have a decent battery life.

[jj]

Posted on May 17, 2011 at 12:37

Second the comment, ''STM32 NOT really designed for Lcd drive.''

Recall that Lcds do not like DC. Should/when you ''turn it off'' your AC scan will be lost - resulting in DC bias which will ''kill'' your Lcd in time. (you thus extend your product from pedom. to ''new art'') Several chip makers offer scanned Lcd ICs. (Maxim) Review of their data may spark some ideas. In the stone age we used 74C4543 ''official'' Lcd digit driver. You may be able to model its output or keep these ''alive'' while the STM32 sleeps...

[obtronix]

Posted on May 17, 2011 at 12:37

Quote:

On 23-06-2008 at 15:45, Anonymous wrote: Second the comment, ''STM32 NOT really designed for Lcd drive.'' Recall that Lcds do not like DC. Should/when you ''turn it off'' your AC scan will be lost - resulting in DC bias which will ''kill'' your Lcd in time. (you thus extend your product from pedom. to ''new art'') Several chip makers offer scanned Lcd ICs. (Maxim) Review of their data may spark some ideas. In the stone age we used 74C4543 ''official'' Lcd digit driver. You may be able to model its output or keep these ''alive'' while the STM32 sleeps... A power switch would work, or maybe setting the LCD GPIO outputs to inputs before sleeping/stopping/standbying, but not enough info in the datasheets on low power modes to know if this would work

[16-32micros]

Posted on May 17, 2011 at 12:37

This is to resolve a web page formatting issue :-(, I've just copied then pasted original messages below :

From “jj.sprague� : Posted 24-06-2008 at 02:45 Forgive me - but I disagree. The issue remains that the Lcd must see an AC driving waveform - with 0V DC bias. No micro can provide such when in power-down/sleep. If its ok to ''extinguish' the lcd while the micro sleeps then powering off will be ok - we killed many an lcd in the olde days by allowing a DC bias to be introduced... From “obtronix� : Posted 24-06-2008 at 04:34 i'm talking about turning the display off during sleep,not actively driving it. No ac, no dc... may or may not be acceptable for his application, don't know anyway many micros can actively drive LCD's during sleep, AC waveforms with no DC From “lanchon� : Posted 24-06-2008 at 05:29 what's the problem with sleeping the processor after each half cycle? would it still use too much power? what if the core regulator is turned off and the GPIOs are placed in high impedance? would the display capacitance be enough to maintain the voltages during the off time? (each common line would be driven by two GPIOs and a pair of voltage divider resistances so that they can be placed in hi-Z.) [ This message was edited by: STOne-32 on 24-06-2008 20:19 ]

[16-32micros]

Posted on May 17, 2011 at 12:37

See this post

http://www.st.com/mcu/forums-cat-6218-23.html

[obtronix]

Posted on May 17, 2011 at 12:37

Quote:

From “lanchon� : Posted 24-06-2008 at 05:29 what's the problem with sleeping the processor after each half cycle? would it still use too much power? Yes, you need to be in standby or stop mode most of the time. hey I see the new STM32 models are in stock now

[asterix]

Posted on May 17, 2011 at 12:37

Hi obtronix, jj.sprague,

Thank you a lot for the pointers, This helps me :) Regards, Asterix