Circuit Project Electronic

If you need to add simple data acquisition capabilities to your PC, then look no further than the Analog Interface Unit. The Analog Interface Unit (AIU) is a simple circuit that connects to a PC parallel port, and allows you to sample and output 8-bit analog signals under software control. Here are some of the features : * 8-bit ADC and DAC * Powered from the parallel port * 1Mohm input impedance. * Software selectable +/-1.25V or +/-2.5V input and output ranges

Read more source:
http://www.alternatezone.com/electronics/aiu.htm
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This small realization, based on one of the most common IC (MAX232) is designed to create a small and convenient TTL to RS232 and vice versa converter. All you need is 4 caps, one IC and 2 connectors. If you want to add a small regulator on the board (already foreseen on the PCB) you just need to add a 78L05 regulator and a cap.

Read more source:
http://users.picbasic.org/Howto/TTL-RS232/ttl.htm
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USB to Serial Adapter RS-232 Serial Port to USB The USB to Serial adapter (converter) lets you use a serial PDA, GPS, cell, etc. with a standard USB port. This adapter is the easiest way to add a serial port to your computer. Many PDAs, digital cameras, GPS units, barcode scanners, and other equipment require a serial connection, and many newer computers don’t have serial ports.

Read more source:
http://electronics-diy.com/electronic_schematic.php?id=565
Thank you.