Computer Interface

Parallel Port Interface with relay

Below are three examples of controlling a relay from the PC's parallel printer port (LPT1 or LPT2). Figure A shows a solid state relay controlled by one of the parallel port data lines (D0-D7) using a 300 ohm resistor and 5 volt power source. The solid state relay will energize when a "0" is written to the data line. Figure B and C show mechanical relays controlled by two transistors. The relay in figure B is energized when a "1" is written to the data line and the relay in figure C is energized by writing a "0" to the line. In each of the three circuits, a common connection is made from the negative side of the power supply to one of the port ground pins (18-25). ..

SmartCard adapter / interface for PC

This smartcard adapter follow exactly the specification ISO 7816. Also, the protocol is the "asynchronous half duplex T=0 protocol" with "active low reset" and "inverse convention" as defined in this standard. The following description may be used in order to connect computers to ISO 7816 compatible chip card systems (e.g. GSM mobile phones or other pay-TV decoding systems) if they also use asynchronous transmission. For smart card systems which use synchronous transmission (e.g. most phone cards) the interface described here will need some modifications. ..

PC RS232 Frequency Counter

This circuit is a stable frequency counter accurate to 5 significant digits. The range is 0 - 30MHz with an input sensitivity of greater then 100mV. The probe connects to the PC serial port. So by using the crystal oscillator already present on your PC serial card and software calibration, the Probes' external circuitry is kept to a minimum. Probe 9 can also be used as a logic probe/analyzer using included software (LPROBE92.EXE)...

PC terminal using a TV

When you use microcontrollers in your designs, sometime you face a problem how to show user required data. Several LEDs, 7 segment display or LCD module can be solution. But if you must show a lot of information simultaneously, it can be difficulty. Large LCD modules are expensive and graphic modules require complicated control. You can solve it with a help of PC. Just send data via serial line to the computer and display everything on computer's display. I have had to solve the same problem some time ago. I have chosen normal small TV set for that. A lot of families change TV in this time because of digital broadcasting or modern flat and slim LCD and plasma displays. So they put older TV set away and it is dormant somewhere. Or you can buy older TV very cheap...

DVI to PAR digital video interface with LCD

This page describes a cheap and simple yet flexible HDMI to parallel 3.3v interface. This allows to connect most LCDs frames to the beagleboard without any further interface required. I am using this myself with some 7inch 800x480 displays which i am using to run Angstrom Linux as well as the maemo on beagleboard project. I have used these lately for some work on Meego. The hardware is rather simple and doesn't consist of much more than the TFP101A panel link receiver from TI. This chip directly outputs 3.3V signals. The dvi2par routes these signals though 22R resistor arrays to reduce reflections. The resulting signals can be fed directly into a LCD screen as depicted below...

If you want a powerful, free and portable compiler for the AVR you'll end up with gcc. Fortunately, gcc is supporting the AVR cpu for quite some time now and e.g. the WinAVR toolchain for AVR development under windows is based on this compiler. Many people have already ported these compilers to MacOS X incl. the fink project and others. Unfortunately i had either trouble getting some parts to install properly (fink didn't offer to install all the required libs) or the compilers were just outdated versions and a long time ago updated to the latest gcc version. I therefore tried my install_avr_gcc.sh script that i am using to achieve the same under linux. ..

Ethernet board for C64 and SX-64

Once i had my SX-64 repaired i wanted to do something cool with it. I learned about people who added ethernet interfaces to their C64 and since i had some spare ones of the required ethernet chips, i decided to build the net64 cartridge. See the image above for my SX-64 with the net64 cartridge installed. The net64 cartridge is compatible to the final ethernet cartridge and can be operated with software developed for the tfe...

Acceleration sensing USB interface

The TiltStick is a small acceleration sensing device in form of a USB stick. It's using a two axis acceleration sensor to measure acceleration (caused e.g. by motion and tilt). The device is emulating a USB joystick and can thus be used in conjunction with any USB equipped host (e.g. a standard PC or the Nokia N8XX family) without any special drivers. The TiltStick is the successor of the Tilt Dongle for Palm OS. Two versions of the TiltStick have been designed based on different 2D accelerometer chips. The slightly smaller one is based on the Analog Devices XL203 (the XL202 may also be used). ..

i2c interface to USB interface

The i2c-tiny-usb project is an open source/open hardware project. The goal of i2c-tiny-usb is to provide a cheap generic i2c interface to be attached to the usb. It is meant as a replacement for those simple and cheap printer port to i2c adapters. A USB solution has several advantages incl. the built-in power supply and a more future proof interface. Furthermore no cpu intense bitbanging is required on the host side. This USB solution even requires less parts than some printer port solutions. While the i2c-tiny-usb was developed under and for Linux it also works under Windows and MacOS X. A windows demo driver and demo application is included to get you started immediately...

80x32 LED matrix display

I recently purchased 10 SLM1608 (SLM1606) LED matrix display units from Ebay (you might also contact the seller directly at op16@gmx.de). These are 16x16 LED matrix units with a green and a red LED per pixel allowing each pixel to be switched to either green, red, amber or off. The goal of this LEDMATRIX project was to build a 80x32 pixel display by arranging the displays in two rows with 5 displays each giving a total of 16*16*2*2*5 = 5120 LEDs to be controlled individually. Fortunately these displays come with interated controllers and the data can be shifted into a single display using as few as 6 digital signals. By multiplexing some of the select signals all 10 displays can be controlled with a total of ten wires. Using a cheap ATmega32 microcontroller all ten displays can easily be controlled and updated in real time...

LCD to USB interface

LCD2USB is a open source/open hardware project. The goal of LCD2USB is to connect HD44780 based text LCD displays to various PCs via USB. LCD2USB was meant to be cheap and to be made of easily available parts. It is therefore based on the Atmel AVR Mega8 CPU and does not require any difficult to obtain parts like separate USB controllers and the like. The total cost (without display and pcb) are about 5 to 10 Euros. LCD2USB currently comes with a simple demo application that works under Linux, MacOS X and Windows...

Frequency Meter using PC

Here is a simple technique for measuring frequencies over quite a wide frequency range and with acceptable accuracy limits using a PC. It follows the basic technique of measuring low frequencies, i.e. at low frequency, period is measured for a complete wave and frequency is calculated from the measured time-period. Cascaded binary counters are used for converting the high-frequency signals into low-frequency signals. The parallel port of a computer is used for data input from binary counters. This data is used for measuring time and calculating the frequency of the signal. The block diagram shows the basic connections of the counters and parallel port pin numbers on 25-pin D connector of a PC (control register 379 Hex is used for input)...

IR remote control for PC

This simple circuit allows you to record any IR remote control signal on your PC, and then play it back. This is particularly useful if you want to control appliances such as TVs, VCRs, CDs etc. from your computer. The device simply connects to the parallel port of your PC. You can also use this circuit to analyze the waveform from any IR remote control. The circuit consists of two parts. The first part is the IR receiver made up of a OP-505 IR photo transistor. This signal is buffered and squared up by the Schmitt trigger inverters (74HC14). The output of this inverter goes directly to the Acknowledge line (pin 10) of the parallel port. The software polls this line in the recording mode and stores the incoming data sequence...

Dive Computer interface RS232

This circuit represents a Dive computer interface for RS232. Uses the MAX232A...

RS-232 Laser Transciever circuit

Laser based projects used to be expensive, until the development of solid state lasers. This project is designed for the entry level laser experimenter. The circuit allows any two computers with serial (RS-232) communication capability to communicate over 200 meters using a laser beam. A low cost transmitter only circuit is also presented here for use in one way communication and other laser based projects. If you are like me and always wanted to buy a laser pointer to play with, but could never find practical uses for one, here are a couple of circuits to convince you to finally make that purchase. Before we begin, however, it is necessary to give a word of warning: Never look directly into the laser beam as eye damage may occur. ..