LCD circuits

This is the first interfacing example for the Parallel Port. We will start with something simple. This example doesn't use the Bi-directional feature found on newer ports, thus it should work with most, if no all Parallel Ports. It however doesn't show the use of the Status Port as an input. So what are we interfacing? A 16 Character x 2 Line LCD Module to the Parallel Port. These LCD Modules are very common these days, and are quite simple to work with, as all the logic required to run them is on board.

Our programmable MP3 player has an interface to an LCD with a HD44780 controller. These are alphanumeric LCDs with one to 4 lines of text and 16 to 40 characters per line. However, these LCDs (and LCDs in general) exist in two varieties: those that require a positive LC-driving voltage and those that need a negative LC-driving voltage. The H0420 (the programmable MP3 player that I referred to earlier) only supports LCDs with a positive LC-driving voltage, because it takes its power directly from a common (asymetric) mains power adapter.

Alphanumeric LCD displays have become very popular for microcontroller applications because they can add a lot to a project in a variety of different ways. A text message giving the user instructions as well as feedback can make the application seem much more "professional" and easy to use. I like to use LCD's to help debug applications, with breakpoints set to display variable and I/O conditions and they are a lot cheaper than using a microcontroller emulator. To top it off, surplus LCD's can be found for a dollar or less.

This is an evaluation use of a small graphics LCD module. Last summer, SG12232C graphic LCD module has been sold sold for 1500 Yens from Akizuki Denshi and I bought it. However I could not find good application for the LCD module and it was going to go to junk box :-) so that I tried to use the LCD module temporary. Only displaying any still image is not cool, first I tried to display an audio wave form in real-time like a digital oscilloscope, and then an FFT spectrum analysis too. The spectrum monitor seems to achived nice performance, in view of it is realized with a cheap microcontroller.

However, the circuit in Figure 1a implements a clocked serial input for an LCD module and allows a µC to communicate with the LCD over just two signal lines. You can fit the circuit onto a small pc board and mount the board directly behind the LCD module. The connection between the board and LCD module comprises just four wires, including VCC and ground. A 74LS164 serial-to-parallel shift register forms the heart of the circuit and communicates with the LCD module in 4-bit mode. The shift register's outputs directly drive the LCD module's data inputs, DB7 through DB4, as well as RS, the control/data select input.

Vacuum fluorescent displays, known as VFDs(because both vaccuum and fluoroscent are hard to spell) are commonly used in VCRs and microwaves. They are relatively bright and have a low power consumption. Some older calculators used them before LCDs became popular. Having obtained a few Futaba VFDs from a surplus dealer, I went about trying to interface it to a PIC. A plea went out on the PIC list and was soon answered by Kalle Pihlajasaari with a few details on VFDs.

Although in abundant use, mini µPs suffer from a low I/O-pin count, which places each pin at a premium. Interfacing a bus-type device, such as an alphanumeric LCD, can use most of the I/O pins. Even placing the display in the 4-bit transfer mode still can cost as many as seven lines. An easier way to save pins uses a lowly 74HC164 shift register to cut the pin count to four I/O lines, PA0 to PA3 (Figure 1).

This is the first interfacing example for the Parallel Port. We will start with something simple. This example doesn't use the Bi-directional feature found on newer ports, thus it should work with most, if no all Parallel Ports. It however doesn't show the use of the Status Port as an input. So what are we interfacing? A 16 Character x 2 Line LCD Module to the Parallel Port. These LCD Modules are very common these days, and are quite simple to work with, as all the logic required to run them is on board.

A very simple circuit to experiment with AT90S2313, 2x16 LCD display and 4x4 keypad. The clock based on 4 MHz crystal, but you can use anyone crystal between 1-4 MHz. The keys with the name "A", "B" ... "F" are typed to the LCD with numbers 10-16. Because the AVR have only 15 I/O pins we are working the LCD display with 4-bit databus. The 4 resistors (10K) are to protect the AVR from the shortcuts as the coloumn of the keypad is change. I make the source code with a simple form, that its mean I don't make any economy to the memory, to understand the beginner how does the circuit its working.

The circuit in Fig 1 provides digital control and automatic thermal compensation for LCD contrast bias. This control and compensation eliminates the need for panel-mount hardware and frequent manual adjustment of LCD contrast in changing temperature environments. Major components in Fig 1 include an inverting current-mode PWM regulator, a programmable digital potentiometer, and a negative-temperature-coefficient (NTC) thermistor. The 5V single-supply circuit consists of all surface-mount components and occupies approximately 6.25 sq cm of board space.

Alphanumeric LCD displays have become very popular for microcontroller applications because they can add a lot to a project in a variety of different ways. A text message giving the user instructions as well as feedback can make the application seem much more "professional" and easy to use. I like to use LCD's to help debug applications, with breakpoints set to display variable and I/O conditions and they are a lot cheaper than using a microcontroller emulator. To top it off, surplus LCD's can be found for a dollar or less.

Almost any 2x16 character LCD module with Hitachi HD44780 controller chip will work. The LCD pin numbers on the schematic are not valid for all LCD modules. Please check the actual signal names on your particular LCD module. The selected DFCW frequency offset will be added to the output frequency when the DFCW input is grounded. This input has a weak pull-up in the PIC.

White LEDs find wide use in backlighting color-LCD screens in most portable devices, such as cellular phones, PDAs, and MP3 players. Multiple LEDs often connect in series to ensure that the same current flows through every LED. To forward-bias these LEDs, a voltage of 10 to 16V comes from an inductor-based boost regulator, such as an SP6690. However, white LEDs are behind the display, whereas boost regulators are on the main pc board, and it is important to minimize the number of interconnects.

A speedometer measures a wheel's rotational speed. Unlike conventional mechanical and moving-magnet designs that use analog moving-pointer displays, the electronic speedometer in this Design Idea features a digital readout and a power-saving device that uses few components. Figure 1 shows the digital speedometer's circuit design. An Atmel AVR AT90S2313 microcontroller, IC1, drives IC3, a 16-character, two-row LCD.

This project demonstrates the use of 16x1 line LCD module to interface with Nitron 16-pin MCU, 68HC908QY4. The original idea came from one evening I went out with my son to the park near my home in Korat. The park has a nice walking way for people to exercise.

The LCD thus saves power by a factor of approximately 1000. Checking an LED is as simple as checking a semiconductor diode but, in the case of LCDs, involves some added complexity. An LCD requires an ac electric field to excite the organic compound in the display. Applying a dc voltage could permanently damage the LCD. The circuit in Figure 1 is a simple configuration to test the performance of an LCD. The circuit produces biphase square waves with negligible dc content. The circuit is based on a CD40106 hex Schmitt-trigger inverter.

The LX1970 light sensor can be used in conjunction with an LCD Front or Back Light Controller such as the LX1992 for LEDs or the LX1689 for CCFLs. This application note describes how to design in the LX1970.

Almost any 2x16 character LCD module with Hitachi HD44780 controller chip will work. The LCD pin numbers on the schematic are not valid for all LCD modules. Please check the actual signal names on your particular LCD module. The selected DFCW frequency offset will be added to the output frequency when the DFCW input is grounded. This input has a weak pull-up in the PIC. The encoder inputs also have internal pull-ups in the PIC. The switches "LOCK", "DFCW" and "CAL" are momentary pushbuttons.

It is sometimes desirable to display the output of a PIC µC graphically, rather than numerically. However, the operation increases system complexity and expense. In addition to the LCD itself, you usually need a graphics controller and at least 1 kbyte of RAM. However, you can obtain a satisfactory plot (Figure 1) without the use of a controller or any RAM. At first glance, the parameters seem daunting.

Vacuum fluorescent displays, known as VFDs(because both vaccuum and fluoroscent are hard to spell) are commonly used in VCRs and microwaves. They are relatively bright and have a low power consumption. Some older calculators used them before LCDs became popular. Having obtained a few Futaba VFDs from a surplus dealer, I went about trying to interface it to a PIC. A plea went out on the PIC list and was soon answered by Kalle Pihlajasaari with a few details on VFDs.