Simple Parallel (Printer) Port Interface

Schematic

Parallel Port Pin Assignments

Parts

Part Total Qty. Description Substitutions U1, U2, U3 3 74LS367 Buffer IC 74367, 74HC367 MISC 1 Case, Wire, Sockests, 18 Pin Socket (For Output), 25 Pin Connector (For Parallel Port), Ribben Cable

Notes

1. I built the interface on a piece of universal solder board due to the large number of wires that must cross. It is also much easier to fix mistakes then on a PC board. I also used a 25 pin crimp connector to connect it to the parallel port. 26 conductor ribben cable was used to link the connector to the board.
2. This interface only offers 5 inputs (on some computers it may be less). For more inputs, see Computerize Your Room/House. If you choose to use the inputs, remember that the voltage level can not exceed 5 volts or fall below ground.
3. This circuit is TTL and therefor must be powered by no more then 5 volts.
4. You can download control software from my files section.
5. For more information on programming the parallel port, see Programming The Parallel Port In QBasic or Programming The Parallel Port In Visual Basic.

Computer Controlled Frequency Counter/Logic Probe

Computer Controlled Frequency Counter/Logic Probe

Schematic

Parts

Part Total Qty. Description Substitutions R1,R2,R3,R4 4 100K 1/4W Resistor R5 1 10M 1/4W Resistor R6, R7 2 3.3K 1/4W Resistor R8 1 390 Ohm 1/4W Resistor R9 1 1M 1/4W Resistor C1, C4 2 0.1uF Ceramic Disc Capacitor C2, C3 2 100uF 16V Electrolytic Capacitor D1 1 1N4148 Signal Diode Any 200mA silicon signal diode D2, D3 2 3.3V Zener Diode D4 1 6.2V Zener Diode U1 1 74HC00 Quad Highspeed NAND Gate U2, U3, U4 3 4021 8 Stage Shift Register U5 1 74HC393 Dual Highspeed 4 Bit Counter U6 1 4040 12 Stage Binary Counter MISC 1 PC Board, Wire, Suitable Probe, DB9/DB25 Connector

Notes

1. Email Richard van Wyk with questions, comments, etc.
2. The software to use this probe can be downloaded using the following link. Note that this software is compiled for Intel x86 platforms and runs under DOS, Win95, Win98 and WinMe. It does not run under any Windows version based on NT including Windows NT 3.51, WinNT4, Win2K, Win2K3, WinXP and Windows Vista. This is because NT based operating systems do not allow direct hardware access.Download Probe Software, Zipped, 19K
   
3. SETPROBE.EXE is the frequency counter calibration program. To give accurate readings the Probe must be calibrated to your PC. SETPROBE.EXE calculates the constant error correction factor for the particular PC serial card the probe is to be used on. The frequency counter corrects for this slight constant error in crystal frequency by using the correction factor contained in PROBE.DAT. To calculate this correction factor, a reliable oscillator of known frequency (eg 2MHz Crystal Oscillator) is required. When CALIBRAT.EXE is run, the Probe will sample the frequency and then ask for the true frequency value in HZ. The frequency entered must be to 1 Hz accuracy (no decimal points) or an error will occur (for example "200123" not "200123.34" or "2003.421 kHz"). The program then calculates constant error correction factor and stores it to PROBE.DAT. Calibration is only necessary once.
4. LPROBE92.EXE is the logic analysis program . Logic states are displayed in real time. This program runs best under DOS (not a DOS window). The sampling speed is adjusted by using the left and right arrow keys.The three triggering modes are:
   
   • TRIG: Starts each scan (left-right of screen) on a negative going edge of logic signal.
   • KEY TRIG: Waits for a key to be pressed before beginning each scan.
   • FREE RUNNING: Not triggered.
   To Toggle between these use the UP / DOWN arrow keys. To quit from LPROBE press escape.
   
5. FPROBE92.EXE is the frequency counter program. The measured frequency is displayed in Hz with commas indicating KHz and MHz. To quit from FPROBE press any key.
6. Serial port pinouts are as follows.
   

   Line	9 Pin	25 Pin
   TD	3	2
   RTS	7	4
   DTR	4	20
   DSR	6	6
   CTS	8	5
   SG	5	7