Computer Controlled Frequency Counter/Logic Probe Circuit

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).

Schematic-

Parts List-
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 or 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) 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

2) 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.

3) 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.

4) 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.

5) Serial port pinouts are as follows.
9pin - 25 pin
TD - 3 - 2
RTS - 7 - 4
DTR - 4 - 20
DSR - 6 - 6
CTS - 8 - 5
SG 5 7

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Car Alarm Arming Horn Beep Canceller Circuit

It's a great convenience that most modern cars come with a built in alarm, however it is nothing but noise pollution that the horn sounds when the alarm is armed. Disconnecting the alarm system from the horn relay will eliminate this, but prevent the horn from sounding in the even of an actual alarm. This circuit serves to silence the arming beep yet maintain the alarm by introducing a small delay into the signal. It sits between the alarm and horn relay. The alarm must provide a constant horn signal for at least 3 seconds before the horn relay is activated. That way the quick "beep" will never activate the horn relay, while the constant alarm signal will.

Schematic-

Parts List-
C1 - 1 - 0.01uF Ceramic Disc Capacitor
C2 - 1 - 100uF 35V Electrolytic Capacitor
R1 - 1 - 1K 1/4W Resistor
R2 - 1 - 10K 1/4W Resistor
R3 - 1 - 15K 1/4W Resistor
R4 - 1 - 470 Ohm 1/4W Resistor
D1, D3, D4 - 3 - 1N4004 Rectifier Diode
D2 - 1 - Red LED
U1 - 1 - 555 Timer IC
K1 - 1 - SPST 12V Automotive Relay
MISC - 1 - Board, Wire, Socket For U1, Case

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Automatic Headlight Brightness Switch Circuit

Driving the highway with your high-beam headlights can really increase your visibility, but can be a blinding hazard for other drivers. This simple circuit can be wired into your headlight switch to provide automatic switching between high and low beam headlights when there is oncoming traffic. It does this by sensing the lights of that traffic. In this way, you can drive safely with your high-beams on without blinding other drivers.

Schematic-

Parts List-
R1 - 1 - 5K 1/4W Resistor
R2, R3, R4 - 3 - 5K Pot
Q1 - 1 - NPN Phototransistor
Q2 - 1 - 2N3906 PNP Transistor
K1 - 1 - Low Current 12V SPST Relay
K2 - 1 - High Current 12V SPDT Relay
S1 - 1 - SPST Switch
B1 - 1 - Car Battery
MISC - 1 - Case, wire, board, knobs for pots

Notes-
1) Q1 should me mounted in such a way so it points toward the front of the car with a clear line of site. Suitable places are on the dashboard, in the front grill, etc.

2) Adjust all the pots for proper response by testing on a deserted road.

3) S1 enables and disables the circuit.

4) B1 is, obviously, in the car already.

5) Before you try to connect this circuit, get a wiring diagram for your car. Some auto manufacturers do weird things with wiring.

6) Connection A goes to the high beam circuit, B goes to the headlight switch common and C connects to the low beam circuit.

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Solid State Tesla Coil/High Voltage Generator Circuit

This is a fun and useful circuit for demonstrating high frequency high voltge. It can produce up to about 30KV, depending on the transformer used. It is cheap and easy to make, thanks to the standard TV flyback transformer used. It can power LASERS (although I have never tried), and even cause a fluorescent bulb to light from as much as 2 feet away.

Parts List-
R1 - 1 - 27 Ohm 5W Resistor
R2 - 1 - 240 Ohm 5W Resistor
BR1 - 1 - 50 Volt, 6 Amp Bridge Rectifier
C1 - 1 - 8000uf, 35 Volt Capacitor
Q1, Q2 - 2 - 2N3055 NPN Power Transistor
T1 - 1 - 24V 5A Transformer (See "Notes")
T2 - 1 - TV Flyback Transformer (See "Notes")
S1 - 1 - 115V 3A SPST Switch
MISC - 1 - Case, Wire, Heatsinks, Line Cord

Notes-
1) T2 is a high voltage flyback transformer salvaged from an old TV, or ordered from Fair Radio Sales (see Where To Get Parts). Look for the biggest, most intimidating transformer you can find. Old tube TV's are a good place to look. The transformer should not have a rectifier built in.

2) You will need to rewind the transformer's primary. First, remove the old primary, being careful not to damage the high voltage secondary. If the transformer is wound with all windings incased in plastic, use another transformer. Second, wind on 5 turns of 18 AWG wire, twist a loop (center tap), and then wind on 5 more turns. This becomes winding C-D. Now, wind on 2 turns of 22 AWG wire, twist a loop, and wind on 2 more turns. This becomes winding A-B.

3) Q1 and Q2 will run HOT if not used with a large heatsink. After the circuit has been running for a minute or two, you should still be able to put your finger on the transistors without being burnt. Also, R1 and R2 will run hot.

4) If you experience arcing on the exposed transformer leads, select a lower voltage for T1. If you are powering the circuit with a power supply (see Power Supply), just crank down the voltage.

5) For a real high voltage output, connect a voltage multiplier (from an old TV or computer monitor) to the output of T2.

6) If the circuit does not work, reverse connections A and B.

7) I finally got around to taking some pictures of the circuit in operation. Here they are:

The first picture is the high voltage generator without the voltage multiplier. Notice how hot the arc looks. The second picture is the high voltage generator with a voltage multiplier installed. Notice how much brighter the arc is.

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Dual Polarity Power Supply Circuit

When working with electronics, you always need one basic thing; power. This power supply is great for powering all kinds of electronic projects. It produces a well filtered, variable 1.2-30 volts at 5 amps. It is easy to build and the parts are realitively easy to find.

Schematic-

Parts List-
C1 - 1 - 14000uF or 10000uf 40 VDC Electrolytic Capacitor
C2 - 1 - 100uF 50Vdc Electrolytic Capacitor
C3 - 1 - 0.1uF Disc Capacitor
C4 - 1 - 0.01uF Disc Capacitor
R1 - 1 - 5K Pot
R2 - 1 - 240 Ohm 1/4 W Resistor(See Notes)
U1 - 1 - LM338K 1.2 to 30 Volt 5 Amp Regulator
BR1 - 1 - 10 Amp 50 PIV Bridge Rectifier
T1 - 1 - 24 V 5 Amp Transformer
S1 - 1 - SPST Toggle Switch
MISC - 1 - Wire, Line Cord, Case, Binding Posts (for output)

Notes-
1) The regulator comes in a TO-3 case and MUST be used with a LARGE heatsink. You may want to mount a small fan to blow air across the regulator (I did).

2) The filter capacitor is large. It won't fit on any board so bolt it to the case.

3) You can, of course, add a volt and amp meter.

4) Since this project operates from 120 VAC, you must include a fuse and build the project in a case.

5) R2 may need to be decreased to 120 Ohm if you experience voltage drift at light loads. 240 Ohm may not load the output appropriately on some regulators. The datasheet for the LM338K does specify 120 Ohm (I suggest you use a 1/2W unit) so you may just want to use 120 Ohm and not bother with the 240 Ohm resistor showin the parts list.

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