Readouts

A project that includes a stage with three selectable gains (0.1, 1.0, and 10) requires that the rotary-gain switch also function to illuminate one of three LEDs. These panel-mounted LEDs serve to indicate the gain in use. This arrangement requires two switch sections—one for selecting the op amp’s gain-set resistor and one to light the corresponding indicator LED. The circuit in Figure 1 requires only one more switch section to provide a true, two-digit, seven-section numeric LED display. The circuit needs no active driver-decoder circuitry.

The circuit in Fig 1 has two sections: an interface/transmitter board and a receiver/display board. On the interface/transmitter board, controller IC1 contains an address decoder and a synchronous state machine. IC2 and IC3 are identical, registered seven-segment HEX transcoders. Listings 1 and 2 contain these PLDs' specifications. You can download the compressed ZIPfile attached to Edn's FTP Site which contains documentation, circuit diagrams, and listings.

Prototyping this simple circuit for my mother to use as a Christmas decoration has reminded me of several useful lessons, the most important of which is "trust the hardware!". You would not believe how many times I went over the wiring of this project looking for problems and subtle trickery, only to find that I had made a silly logical error in the firmware and that the hardware was in fact working perfectly. This illustrates the crucial importance of the First Law of Digital Circuit Design: Everything is a software problem.

The indirect addressing method is the way of doing the reading/the writing from/to the memory by setting the address of the memory to the FSR register. When using this method, the access address of the memory can be calculated by addition or subtracting and the processing of access to the continued memory is possible to do easily.

On this page, I will introduce the electronic signboard with PIC16F84A. 112 LEDs are used for message display and 50 LEDs are used for around. Latch registers by CPLD are used for the display of the LEDs. So, LEDs can be brightly lit up compared with "Signboard". For the details of CPLD, refer to the following. "7bits x 16rows Latch Register for Signboard" "5bits LED Shifter for Signboard"

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.

You must be able to recognise components such as capacitors, diodes, zeners, transistors and resistors to build 5x7 Display project. This information is covered in our BASIC ELECTRONICS course and a complete set of circuit symbols can be found HERE.

This sign I designed uses no microprocessor. It has an eprom and multiple counters. As in most electric signs, the LEDs are matrixed, and strobed very quickly to make it possible for all 70 LEDs to appear lit. This sign is strobed horizontally, unlike most large signs which are strobed vertically. I did it this way because electrically it was simpler. The eprom has 8 outputs, of which I used 7 of them to drive the 7 horizontal rows. The eprom outputs are not strong, so they are buffered. The 10 vertical columns are activated in sequence, giving a 1/10 duty cycle.

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.

HamCam-ID'er is a tiny digital voice playback device that is designed to announce your personal ham call letters every few minutes. Its small size is perfect for mounting on video equipped R/C model aircraft.

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.

The circuit uses a serial-in-parallel out shift register, 74HC595 for receiving serial data from uController board. See example of U5 in the schematic, SER is for data input, SRCLK is shift clock and RCLK is Latch clock. Each data bit is shifted into the register on rising edge of the shift clock. When all data bits are shifted into the 8-bit register, the rising edge of RCLK will clock the data to be latched at each output bit, i.e. QA - QH.

This holiday season, I was asked by a colleague to build him a LED flasher for a Christmas card he is giving his significant other. As usual, I got a little carried away with this project :-) The result is a "Saturday arvo project" circuit which may be of interest to beginner hobbyists keen to experiment with the popular PIC16C84/16F84 microcontroller. Briefly, it's a 4x4 pixel animated LED billboard of the type commonly seen at railway stations, in store windows and so on - only much smaller, of course.

This sign I designed uses no microprocessor. It has an eprom and multiple counters. As in most electric signs, the LEDs are matrixed, and strobed very quickly to make it possible for all 70 LEDs to appear lit. This sign is strobed horizontally, unlike most large signs which are strobed vertically. I did it this way because electrically it was simpler. The eprom has 8 outputs, of which I used 7 of them to drive the 7 horizontal rows. The eprom outputs are not strong, so they are buffered. The 10 vertical columns are activated in sequence, giving a 1/10 duty cycle.

The circuit in Figure 1 uses a PIC16C55 µP to read 10-bit binary data and directly display the data in decimal format on three common-cathode LED displays. If value of the data exceeds 999, the displays show three hyphens (---) to represent overflow. The PIC16C55 has high drive capability. Each output pin can source 20 mA and sink 25 mA; the outputs can thus directly drive the LED display.

This is one of the most accurate and simplest LC inductance / capacitance Meters that one can find, yet one that you can easily build yourself. This LC Meter allows to measure incredibly small inductances starting from 10nH to 1000nH, 1uH to 1000uH, 1mH to 100mH and capacitance from 0.1pF up to 900nF. LC Meter's circuit uses an auto ranging system so that way you do not need to spend time selecting ranges manually. Another neat function is the "Zero Out" switch that will reset the initial inductance / capacitance, making sure that the final readings of the LC Meter are as accurate as possible.