LCD Displays
I use LCD displays in many of my
projects. The "standard" or most widely used LCD is a 2 line by 16
character alphanumeric display with a parallel interface to the
processor, and a HD44780 controller. It is readily available and inexpensive. (PIC
Example, AVR Example).
This type of display comes in many flavors, typically from 1 to 4 lines
and from 8 to 40 characters. It is simple to interface with your
microprocessor if you have enough I/O ports available (only 4 of 8 data
lines are needed) and either compilers provide support for them or libraries
are available. You specify the port names you use and the
number of rows and columns, usually in a header file. This display
always has a 14 or 16 pin interface, 14 pins for the display and 2 more
pins if there is a backlight.
Another kind of LCD display I have used has no
decoder built in, and you have to drive each segment of each character
yourself (much like an LED display). This
example uses a simple, cheap 3 digit display, the Lumex LCD-S301C31TR (DigiKey 67-1788-ND). The advantage
is low cost and power consumption. The disadvantage is the need for
lots of I/O lines, and no backlight. Bigger displays with
more digits are available, but some kind of decoder or multiplexer must be
used. Also the display is static, and requires periodic polarity reversal or else it fades out. A good
write-up on the subject can be found here.
Then there is the KTM-S1201, a 12-digit mostly numeric display, which I have documented on a
separate page here.
Many inexpensive displays have no backlight and depend on ambient
light and a reflective layer behind the display for visibility. Others
use a backlight to enhance the display in low light conditions. Still
others need a backlight on or nothing will be seen. There is a lot of
information on this on the internet; start with Wikipedia
if you like. I find that backlighting improves the visibility greatly,
but at the cost of power; typically a backlight requires 10mA or so at 5V. If
power consumption is an issue a pushbutton can be used to activate the
backlight.
Special care must be taken with displays with backlights. Some have
current limiting resistors built in and some don't. If you need one and
leave it out, your backlight will last about 1 millisecond and never
work
again. The display may not be completly useless, depending on
the technology used by the display. To be safe, I place a 100 ohm
resistor in series with the backlight and a variable power supply and
start from 0 volts. I turn up the voltage and watch the current draw,
quickly getting an idea what kind of backlight it is. Some need 10 or
47 or 120 ohms, some need nothing or a small resistance like 2.7 ohms.
More on backlights from Wikipedia.
Dennis Che has written a great introduction to LCD displays, All About Character LCDs. I can't find a link to it anymore, so I placed a copy of it here.
Update.
I stumbled across an interesting and inexpensive graphical display in
2012/04, the Nokia 5110. It is 48 x 84 pixels, and the support code
from the seller included a small alphanumeric font giving 14 characters
and 6 rows, and a large numeric font giving 7 numbers and 2 rows.
Power is limited to 2.7 to 3.3 Volt range. One vendor is Sparkfun, and the price was US$9.95. They may be available from other vendors,
with various support code that is mainly Arduino based. My first
project using this display was a clock
using an ATmega88 and no RTC chip. The display is serial accessed,
using the AVR's SPI port and 3 other control lines (plus backlight).
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