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Computer Interface Circuits

Computer Interface: 
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Last Updated: October 24, 2017 02:54 PM

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

PreAmplifier Computer Microphone This circuit was submitted by Lazar Pancic from Yugoslavia.  The sound card for a PC generally has a microphone input, speaker output and sometimes line inputs and outputs.  The mic input is designed for dynamic microphones only in impedance range of 200 to 600 ohms.  Lazar has adapted the sound card to use a common electret microphone using this circuit __ Designed by Lazar Pancic from Yugoslavia

Precision level shifter has excellent CMRR 15-Apr-04 EDN-Design Ideas Most designers make level shifters with op amps and 1%-tolerance discrete resistors.  Discrete-resistor mismatching limits the op amp's CMMR(common-mode rejection ratio] to 40 dB, so you cannot use op amps in circuits that require high CMRR.  Differential amplifiers contain precision matched internal resistors, so ICs such as the INA133 can readily achieve CMRRs of approximately 90 dB __ Circuit Design by Ronald Mancini, Texas Instruments, Bushnell, FL

Precision peak Detector uses no precision components 10-Jun-04 EDN-Design Ideas When you need a precision peak detector, you would usually implement it with one or several op amps and a few other associated components.  This technique usually works well unless your design requires operation higher than a few kilohertz.  In designs requiring such operation, the accuracy of the circuit severely deteriorates unless at least one of the amplifiers has a high slew rate and frequ __ Circuit Design by Jim McLucas, Longmont, CO

Preprocessor for rotary encoder uses PAL 08/04/01 EDN-Design Ideas Rotary encoders usually provide quadrature pulses that indicate both the amount of rotation and the direction(Figure 1).  A microcontroller can calculate the rotation direction and keep track of angular movement.  Many microcontrollers' interrupt inputs, such as those on the Zilog Z86C90, can detect only a falling edge __ Circuit Design by David Rathgeber, Alles Corp, Toronto, ON, Canada

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Printer port activates CMOS switches 05/02/02 EDN-Design Ideas The cost-effective design in Figure 1 provIdeas control for CMOS switches without the need for an external power supply.  Analog switches such as those in the MAX4663 are ideal for use in low-distortion applications.  They are preferable to electromechanical relays in automatic test equipment or other applications in which you need current switching __ Circuit Design by J Jayapandian, IGCAR, Tamil Nadu, India

Printer Port Controls A/D Conversion 12/19/96 EDN-Design Ideas The circuit in Figue 1 uses a microcontroller (PIC16C71] as an A/D converter and a data organizer.  The circuit plugs directly into a PC printer port and needs no external power supply.  Under the control of the Borland C program in __ Circuit Design by Yongping Xia, Philips Lighting Electronics Co, Torrance, CA

Printer Port Controls A/D Conversion 12/19/96 EDN-Design Ideas The circuit in Figue 1 uses a microcontroller(PIC16C71] as an A/D converter and a data organizer.  The circuit plugs directly into a PC printer port and needs no external power supply.  Under the control of the Borland C program in Listing 1, the µC selects one of three analog channels, performs A/D conversion, sends low and high nibbles of converted data back to the printer port, and waits for the next command __ Circuit Design by Yongping Xia, Philips Lighting Electronics Co, Torrance, CA

Printer Port Controls Amplifier's Gain 10/26/95 EDN-Design Ideas The circuit in Fig 1 lets you use a PC's printer port to set the gain of an inverting amplifier.  The circuit uses a 4-to-1 analog multiplexer, IC1, to select a pair of external resistors.  The multiplexer's connection scheme ensures that the on-state resistance of the analog switches does not affect the performance of the circuit.  The on-state series resistance is negligible in comparison with the high input impedance of the op amp.  The op amp's gain is, thus, the ratio of the two network resistances R2/R1 __ Circuit Design by Bogdan Manolescu, Gunicom Professional, Bucharest, Romania

Printer port controls reference generator 09/28/00 EDN-Design Ideas Figure 1 shows a programmable, precision reference-voltage generator.  A PC's printer port controls the generator.  The voltage range is 0 to 4.0955V in __ Circuit Design by Yongping Xia, Teldata Inc, Los Angeles

Printer port controls video multiplexe 08/01/96 EDN-Design Ideas The circuit in Figure 1 is a four-channel video-signal multiplexer.  Eight-bit binary data(of which only 3 bits are used] from a PC's parallel printer port controls the multiplexing operation.  The inputs for all the channel __ Circuit Design by Shyam Tiwari, SR&HPG, IGCAR, Kalpakkam, India

Printer Port hosts precision analog I/O board 02/02/95 EDN-Design Ideas The 12-bit analog I/O board in Fig 1 plugs into a PC's printer port.  Thus, you can move the board around your laboratory more easily than you can exchange A/D boards that plug into the PC's backplane.  The board handles eight 1-kHz input signals ranging from 0 to 5V max.  IC1 is a serial, 12-bit A/D converter having an internal 4.096V reference and an internal track-and-hold circuit.  Op-amp IC2 provIdeas a low-impedance source for IC1.  IC2 has a VOS of 70 µV,  __ Circuit Design by Huw Jones, Gyrus Medical Ltd, Cardiff, Wales, UK

Printer Port Records Digital Waveforms 06/18/98 EDN-Design Ideas (File includes several circuitsscroll to find this one)  To record or capture special waveforms, those that appear once or have no fixed frequency, the usual technique is to use a logic analyzer or a storage oscilloscope.  However, these tools are very expensive.  Moreover, because of limited memory, a storage scope can record fewer than 1000 samples.  The technique presented here provIdeas an alternative method to recording digital waveforms.  The idea is to use the PC's printer port to sample waveforms, and the PC's memory to store data.   __ Circuit Design by Dean Shen, Dycam Inc, Chatsworth, CA 

Printer Sharing Switch I had two computers, a Mac Mini and a generic Windows computer.  Both were on different networks, but in the same room, and I wanted to share a Lexmark USB laser printer between the two of them.  I ended up making this switch to share the printer between the two computers __ Designed by Dick Cappels

Printer-Port Data Appears as Bar On PC Screen 06/09/94 EDN-Design Ideas Using the circuit in Figure 1, a PC's printer port can accept 8-bit parallel data.  The 74HC241 in the circuit is a data buffer as well as a high/low nibble selector.  The Borland C program in Listing 1 reads the high and low nibbles, reforming the 8-bit data and converting them to a vertical bar on the PC's screen.  Moreover, the program can compare the input data with preset high and low limits, sending the results of this comparison back out through the printer port. __ Circuit Design by Yongping Xia, EBT Inc, Torrance, CA

Program “Excelerates” Microcomputer-I/O Allocation 112/05/08 EDN-Design Ideas Use Microsoft Excel to organize how you assign I/O functions to microcontroller pins __ Circuit Design by Aubrey Kagan, Emphatec, Markham, ON, Canada

Program Converts Hex to Floating Point 07/20/95 EDN-Design Ideas You might need to use floating-point variables in some embedded software algorithms.  You'll find this easy to do because all modern C compilers come with a floating-point library.  However, when you're debugging a routine, you sometimes need to "peek" or "poke" a floating-point variable when all you have available is a hexadecimal interface.  This scenario __ Circuit Design by John Santic, Consultant, Frederick, MD

Program converts temperature from RTD sensor 06/05/97 EDN-Design Ideas   100V, platinum resistance-temperature-detector(RTD]sensor provIdeas an accurate means of obtaining temperature readings.  Platinum sensors have a nonlinear resistance-vs-temperature characteristic; therefore, for __ Circuit Design by Robert Ruehle, Relco Products, Denver, CO

Program Designs single-supply op-amp 10/26/95 EDN-Design Ideas Mathematically, there is no difference between single- and dual-supply op-amp designs, except for the signal reference.  Dual-supply designs inherently reference signals to ground.  However, you must use biasing to reference signals to ground in a single-supply design, because the signals are inherently referenced to VCC/2.  This requirement for external bias schemes complicates the design procedure.  The Basic program, which you can download from.    __ Circuit Design by Ronald Mancini and Dave Culver, Harris Semiconductor, Melbourne, FL

Program Excelerates Microcomputer-I/O Allocation 12/15/08  EDN-Design Ideas Use Microsoft Excel to organize how you assign I/O functions to microcontroller pins __ Circuit Design by Aubrey Kagan, Emphatec, Markham, ON, Canada

Program Flags Dangerous DOS Commands 02/02/95 EDN-Design Ideas Windows users still perform many small housekeeping tasks, such as renaming, moving, or deleting files, by switching to DOS, because DOS is much faster than the time-consuming, icon-driven facilities of Windows.  However, you shou __ Circuit Design by M N Jayaram, BARC, Bombay, India

Program generates Braille dot code 12/19/96 EDN-Design Ideas The Basic training program in Listing 1  helps visually handicapped people easily learn Braille dot code with the help of a trainer.  The trainer generates six-pin Braille code using six solenoids operating on an LPT1/2 either by directly connecting the low-power solenoids to the data bits of the parallel port or by driving solenoid pins(pull-out type] using an UN2003 power driver(Figure 1).  Push-in type solenoids require complemented(0 for 1 and 1 for 0] Braille-code data bits or an extra inverter on the LPT1 port __ Circuit Design by Jose Carlos Cossio, Santander, Spain

Program Helps Convert Orcad Libraries 09/14/95 EDN-Design Ideas A simple Borland Turbo C 2.00 program, BIT2VEC.   C, is useful for anyone using OrCAD SDT CAE software.  The program, which you can download from EDN's FTP server(DI #1755], helps to convert OrCAD libraries from bit map to vector format __ Circuit Design by Vincenzo Carlotti, Roland Europe SPA, Acquaviva Picena, ITALY

Program Matches Filter-Network Impedances 07/20/95 EDN-Design Ideas In RF circuits, it's often necessary to match one impedance to another.  The program in the Listing 1 can design a network to match any resistive impedance R1 to another R2(where R1 is less than R2] at a specified frequency and specified Q.  The program employs a lossless(in theory] network that uses just capacitors and inductors.  Five matching networks __ Circuit Design by David Kirkby, University College, London, UK

Program provides integer to binary Conversion 03/02/98 EDN-Design Ideas (File had multiple circuit ideas.  Scroll to find this one.)Binary numbers rarely appear in applications of C or C++ programs, so any reference to converting from an integer to a binary number is usually relegated to a few simple examples in the appendix.  However, when you're working with codes for communication systems, terms such as parity, checksum, distance, weight, and block codes are much easier to verify with a check solution when they are in binary form.   __ Circuit Design by Bert Erickson, Fayetteville, NY

Program provides ISA-Bus DLL for Window 09 May- 96 EDN-Design Ideas Windows commonly uses a dynamic link library(DLL]to create subroutines and procedures that all compatible software can call.  A DLL is an executable file, with extension.   DLL, that a program can load and unload as required.  However, not all Windows-based software can read from and write to the ISA bus in a PC.  The DLL described here provIdeas 8- and 16-bit I/O reads and writes to the ISA bus __ Circuit Design by Paul Kemp, NASA Johnson Space Center  Houston, TX

Program the AT89S8252 & 89S53 with Easy-Downloader V2.0 Upgraded EZ52 to EZ53.  hex enabling the Easy-Downloader to program 89S8252 and 89S53 chips without any modifications __ Designed by Wichit Sirichote

Program turns PC sound card into a function generator 09/02/99 EDN-Design Ideas You can use a low-cost PC sound card as an analog-function generator by controlling the PC with the program "SoundArb.   " [To obtain SoundArb, download di2409setup.   exe, a 1.06-Mbyte self-extracting installation program.   ] __ Circuit Design by David Sherman

Programmer for Atmel AVR Controllers USBasp is a USB in-circuit programmer for Atmel AVR controllers.  It simply consists of an ATMega48 or an ATMega8 and a couple of passive components.  The programmer uses a firmware-only USB driver, no special USB controller is needed.  

Programmer Hardware Tester Notice that the schotty diode allows the DIY Programmer to feed its VCC without its VCC being shorted to the PIC's normal power supply.  A tiny DIP switch will also work in place of the diode.  NOTE : the diode is very convenient when developing the code, but it drops about 100mV of the VCC provided (but was never an issue in my designs.  Simply do NOT power the PIC while programming it

Programming adaptor for 8 & 28 pin AVR Microcontrollers using ISP Okits not pretty, but its practical.  The 20 pin connector at the far right is left over from a diffferent project and is no longer used.  This adaptor lets me program 8 or 20 pin DIP devices using the In-System Programmer   (ISP) described in Atmel's AVR910 application note.  This circuit provides power and clocks for the part to be programmed and power to the ISP circuit.  When programming 8 pin devices, the part is positioned toward pins 1 and 20 of the socket such that the 8 pins of the chip occupy the pins 1, 2, 3, 4, 17, 18, 19, abd 20 of the programming socket.  In the case of an 8 pin part being programmed, the SPST switch that grounds pin 4 must to be closed.  Conversely, when programming a 20 pint part, the switch on pin 4 must be open so the crystal can be used for the clock for the part being programmed.   __ Designed by Dick Cappels

ProgrAmpredicts VSWR-mismatch RF uncertainties 02/01/01 EDN-Design Ideas Hewlett-Packard(now Agilent Technologies] once offered a useful little cardboard slide rule for calculating the uncertainty in RF  measurements stemming __ Circuit Design by Steve Hageman, Agilent Technologies, Santa Rosa, CA

Protect Computer's Input 05/26/94 EDN-Design Ideas The circuit in Fig 1 performs input protection, level translation, isolation, and debouncing.  The circuit allowed the output of a relay driver to connect to a computer even though the relay driver delivered a voltage as  __ Circuit Design by Ang Tzu Seng, Halliburton Drilling Systems, Singapore

Provides 4- to 20-mA loop for microcontrollers 05/27/04  EDN-Design Ideas The 4- to 20-mA current loop is ubiquitous in the world of controls in manufacturing plants.  Discrete logic, microprocessors, and microcontrollers easily cover the digital portions of control schemes, such as limit switches, pushbuttons, and signal lights.  Interfacing a 4- to 20-mA output to a rudimentary microcontroller can be problematic __ Circuit Design by Robert Most, Dow Corning Corp, Auburn, MI

PS/2 Keylogger based on PIC12F675 This is a keylogger based on PIC12F675 with 64K eeprom (24LC512).  When keylogger is connected between PC and keyboard it will record every keypress to memory.  By pressing a button recorded data will be sent back to PC so user can read it.  No need

PTT & soundcard interface for the TM255/455 Ham RadioModems and Soundcard interfaces __ Designed by Guy Roels ON6MU

PTT and/or soundcard interface Ham RadioModems and Soundcard interfaces __ Designed by Guy Roels ON6MU

Pulse-Modulated Interconnect Cuts PLD Pinout 03/28/96 EDN-Design Ideas The number of output pins available often places limits on erasable-PLD(EPLD] designs.  These limitations are especially true when a number of multibit signals emanate from the same device.  An N-bit signal and its data strobe take up N+1 output pins.  This number of pins can sometimes take a disproportionately large amount of I/O resources compared __ Circuit Design by V Krishnamurthy, Naval Physical and Oceanographic Laboratory, Kochi, India

Push Button Switch Debouncer This circuit will remove the transient spikes and contact bounces from a non-latching push button switch.   __ Designed by Andy Collison

Pyranometer to Current Converter Simple circuit that enables long cable wiring for pyranometer.  Built with TI rail-to-rail opamp, TLV2451.   __ Designed by Wichit Sirichote

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