Microcontroller with a numeric LCD reflective display without a driver - Page 1
Forum section: electronics / general

author: bipolunipol
author_rank: Contributor
timestamp: March 04, 2021, 09:06:51 am
content: Hello,I've got a display: LCD-S401M16KR (working at 3V)https://www.lumex.com/datasheet/LCD-S401M16KRThe display doesn't have any driver, it is a simple digital LCD panel.Now I would like to use some microcontroller to control it. At the beginning it was supposed to be ATTINY816, but I have to do everything software. That's why I decided to check the PIC16LF1902 microcontroller with LCD driver.https://www.microchip.com/wwwproducts/en/PIC16LF1902It has hardware support for displays and supports multiple sleep modes with the display on. Unfortunately I have a problem with another thing. The power of the LCD in this microcontroller is taken directly from Vdd. When the supply voltage is stable, the contrast does not change. But because I power the system from a LiPo battery - the voltage changes and I see it in contrast. I cannot use a stabilizer, even LDO, because there is too much voltage drop and energy loss. I also don't want a switching-mode power supply because it generates a lot of noise and my device is a radio system.What can I do in this case to stabilize the contrast? Maybe there are better microcontrollers with voltage stabilization? I'm looking for something cheap...

author: Kleinstein
author_rank: Super Contributor
timestamp: March 04, 2021, 10:56:50 am
content: An LDO should be OK for voltage stabilization. The µC should not consume much power and thus the dropout can be low - down to the < 50 mV range. One would even save power, as the µC would consume less power when running at some 3 V instead of 4.1 ... 3 V or some 3.6 V on average. Expect a reduction of the current about proportional to the voltage - so some 20% less current.

author: bipolunipol
author_rank: Contributor
timestamp: March 04, 2021, 02:09:48 pm
content: Quote from: Kleinstein on March 04, 2021, 10:56:50 amLDO like MIC5501-3.0YM5-TR?I guess there is no better microcontroller than the PIC16LF1902 in this price range? This is the cheapest chip from Microchip:https://www.microchip.com/design-centers/lcd/products/integrated-segment-lcd-driversBut maybe there is an alternative?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 04, 2021, 03:01:16 pm
content: QuoteAre you sure ?is the MCU driving things that need >3.3v?The LDO itself will draw a few tens of microamps, and running the MCU at 3.3 or 3.0V will reduce its active power draw, probably by significantly more than the LDO's quiescent current.The PIC16LF1902 does have an internal LCD voltage reference option. It also has some contrast control functionality, so if the internal reference is unsuitable for some reason, maybe you could dynamically adjust contrast based on battery voltage

author: bipolunipol
author_rank: Contributor
timestamp: March 04, 2021, 04:52:51 pm
content: Quote from: mikeselectricstuff on March 04, 2021, 03:01:16 pmI checked in the datasheet - the reference voltage can only come from Vdd - the drawing from the datasheet is in the attachment.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 04, 2021, 05:28:41 pm
content: Quote from: bipolunipol on March 04, 2021, 04:52:51 pmThe datasheet seems a bit unclear on this, for example in the DC characteristics section, it lists "Fixed voltage reference voltage for LCD bias, initial accuracy" ( D003B).There is also mention of the FVR in the LCD section, but not the LCD module section - could be some bad cut/paste, or a change in spec at some pointHowever it looks like an external bias voltage can be applied via the VLCD3 pin if the VLCD3PE bit is enabled, so that might be an option.And the contrast control register may have enough range to adjust contrast based on supply voltage.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 04, 2021, 05:31:14 pm
content: Also note that the LF version has a maximum supply voltage of 3.6V, so you're probably better off running from a regulator anyway. is there a reason you can't do this ?

author: bipolunipol
author_rank: Contributor
timestamp: March 04, 2021, 05:54:14 pm
content: Quote from: mikeselectricstuff on March 04, 2021, 05:31:14 pmI think I'll use LDO after all. MIC5501-3.0YM5-TR has a drop of approximately 50mV at 100mA. My device draws this much current when the vibration motor starts. And normal work is about 10mA. I think that the vibration motor will be connected outside the regulator (directly to the battery), so I can assume that the device uses only 10mA.BTWAnd what is the alternative to this PIC16LF1902?

author: neil555
author_rank: Contributor
timestamp: March 04, 2021, 07:09:50 pm
content: The STM8L052C6 might be a possibility (though slightly more expensive than the PIC)

author: oliviasmithh900
author_rank: Contributor
timestamp: March 07, 2021, 01:12:48 am
content: For TFT LCDs, Arduino Mega works best with LCD shield.

author: YurkshireLad
author_rank: Frequent Contributor
timestamp: March 07, 2021, 02:09:31 am
content: Forgive me if I'm way off base, as I'm really a beginner. Would something like this work:https://abra-electronics.com/ics-semiconductors/4000-series-dip-package/4543-ic-cmos-bcd-to-7-segment-latch-decoder-driver-for-liquid-crystal-displays-4543.html

author: fchk
author_rank: Frequent Contributor
timestamp: March 08, 2021, 12:06:57 pm
content: Quote from: YurkshireLad on March 07, 2021, 02:09:31 amOnly for static LCD glasses. The OP has got a multiplexed glass, which is much more complex to drive.

author: bipolunipol
author_rank: Contributor
timestamp: March 09, 2021, 04:41:53 am
content: Quote from: neil555 on March 04, 2021, 07:09:50 pmUnfortunately this microcontroller is poorly available. Now I am considering one more option. What if I operated the display programmatically? From the cheap ATTINY816 microcontroller. It is very difficult?

author: fchk
author_rank: Frequent Contributor
timestamp: March 09, 2021, 11:58:33 am
content: Quote from: bipolunipol on March 09, 2021, 04:41:53 amWon't work. You will damage your LCD glass. Your glass is 1:4 multiplexed, and for this reason you will need at least four distinctive voltage levels to drive the display properly so that all pins are DC-free (pure AC). This is not really possible with digital outputs. A static display with only one backplane and a pin for each segment would work.PS: You may consider PIC16F19156. Digikey has 732 in stock in SDIP28 package. and 820 of the LF version.fchk

author: PCB.Wiz
author_rank: Super Contributor
timestamp: March 10, 2021, 08:13:54 pm
content: Other possible MCUs to look into could beNuvoton N76E616AL48Nuvoton ML54 seriesNuvoton ML56 series

author: harerod
author_rank: Frequent Contributor
timestamp: March 10, 2021, 08:35:30 pm
content: Quote from: fchk onYesterdayat 12:58:33 pm>Quote from: bipolunipol onYesterdayat 05:41:53 am. . .Won't work. You will damage your LCD glass. Your glass is 1:4 multiplexed, and for this reason you will need at least four distinctive voltage levels to drive the display properly so that all pins are DC-free (pure AC). This is not really possible with digital outputs. A static display with only one backplane and a pin for each segment would work.PS: You may consider PIC16F19156. Digikey has 732 in stock in SDIP28 package. and 820 of the LF version.fchk. . .Interesting that you should mention PIC. I did this design a while agohttp://harerod.de/applications_eng.html#allTimerMCU was a PIC16F57 running at 8192 instructions per second, the glass required three level multiplexing. The currents for LCDs are so low that the resistor values can be quite high. Just check the datasheet.How this fits with the requirement to adjust the contrast due to supply voltage remains to be seen.