A simple terminal program on a PC can have a lot of uses. The hang-up is that most of those uses involve communicating with a device running on 5 volts. I've done several schemes over the years but this one is my favorites. [img:60e1b47cb8]http://www.circuitdb.com/download.php?fileID=139[/img:60e1b47cb8] So I built it into a stand-alone box. This design steals the +12 and -12 power from the computer's serial port. It puts out a very clean rs-232 level signal back to the computer. The output of this device is open-collector with no pull-up to +5. The pull-up is the job of the other...

I noticed allot of people like to use the 7V fan mod, this is fine I suppose but it is very inefficient, and it doesn't allow for RPM monitoring. I have Built a fan controller out of fairly cheap and readily available parts that is extremely efficient, reliable and doesn't endanger your computers PSU. I feel very sure that anyone who knows how to solder can build this device, whether they understand the electronic workings behind it or not. For those of you who don't know what Pulse Width Modulation is and why it is more efficient than voltage drop speed control read the following...

The diagram below shows 5 switches connected to the 5 input lines of the parallel port. An external 5 volt power supply is used to provide high logic levels to the input pins when the switches are open. Three 1.5 volt batteries in series can be used to obtain 4.5 volts which is close enough. The 330 ohm resistors in series with the port connections provide some protection in case a connection is made to the wrong pin. If you are sure of the connections, the 330 ohm resistors can be left out and the switches connected directly to the input pins. The negative side of the power supply should be...

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...

This circuit was designed to control a 32 channel Christmas light show from the PC serial port. Originally designed with TTL logic, it has been simplified using CMOS circuits to reduce component count. It is a fairly simple, reliable circuit that requires only 4 common CMOS chips (for 8 outputs), an optical isolator, and a few discrete components. The schematic diagram illustrates the circuit with 16 outputs which can be expanded with additional 8 bit shift registers. [b:22d2c00d68]Disclaimer[/b:22d2c00d68] This circuit requires physical connections be made to the computer's serial...

This regulator uses a P-FET to change the positive supply voltage to a FAN an NTC resistor mounted on the device that needs cooling will change the fan speed, the temperature on the heat sink will therefore be constant, while the FAN speed will change, depending on power disipated The RPM output signal from most FAN types will continue to function, due to the positve voltage regulation. There is many other ways to do this, but since I have fine access to P-FETS and they have super hight gain, a perfect solution! The Fan regulator schematic, the gate capasitors filter the NTC voltage...

This is a simple I/O interface using an AVR microcontroller. The i/o pins are controlled by the AVR and can be used to drive LEDs, control RC servos, etc. Using the attached relay circuit it can also be used to control relays. This schematics also provides a programming interface....