Lightning Detector. Make sure to see the several readers' versions

Transcription

1 Lightning Detector Make sure to see the several readers' versions The following circuit is an improved version of my original Lightning Detector designed to run on a 5 volt supply. The new circuit features a superior RF section with a single resonance near 300kHz and plenty of sensitivity. The potentiometer was eliminated; simply adjusting the length of the telescopic antenna will give the desired sensitivity. The circuit supply voltage was increased to 5 volts to allow the use of commonly available molded power supplies instead of batteries. Another not-so-obvious feature is that I have plenty of the inductors! (For inductors charles@wenzel.com.) The basic receiver is shown below. The antenna is a telescopic antenna that extends to two or three feet, the length is not critical. A high-value resistor (270k) is connected from the antenna to ground to control the Q and this value may be lowered if the circuit seems unstable but too low a value will destroy the sensitivity. The 10 mh and 1 mh ( not uh) chokes are molded types but most moderately high-q inductors will work fine and the rest of the parts are run-of-the-mill and not particularly critical. The transistors are all general-purpose types. Note: This circuit is intended to be used with one of the lamp options and any or all of the other options. If no lamp is desired, add a 1 k resistor from the "pulses" output to 5 VDC.

2 Below is an experimental version with an additional diode across the 82k. The diode helps the flasher to trigger on smaller pulses. the 82k may be 100k, if desired. Theory of operation: The antenna, 10 pf capacitor, and the two inductors form a resonant tank at about 300 khz, a good frequency for receiving energy from lightning. The two series inductors act as a matching network, feeding Q1 with a lower impedance version of the signal received by the antenna. The 270k resistor lowers the Q of the resonant tank to prevent oscillation. Q1 amplifies the 300 khz bursts and applies the larger signal to the base of a PNP transistor that forms a monostable "flasher" circuit with the last NPN transistor. When the RF signal pulls the PNP base voltage below the voltage on the 10 uf capacitor (plus about 0.6 volts) the PNP turns on, turning on the NPN. Since the NPN is connected to the base of the PNP through the 82 k resistor, the PNP turns on even harder. This regenerative action causes the circuit to turn on quickly and fully, pulling the "pulses" line to nearly zero volts. The circuit stays on until the 10 uf capacitor discharges at which point a similar reverse regenerative action causes the circuit to quickly switch off. The capacitor then quickly charges through the 1k resistor (in one of the lamp circuit options) and the diode and is ready for another pulse. The prototype is built into a phenolic box using point-to-point wiring. The power switch is a single pole, double throw type with a center-off position. The power supply is connected to the center terminal and the speaker is connected to one of the outer terminals. Both of the outer terminals are also connected to the other circuitry through a couple of silicon diodes, one from each terminal. One diode keeps the speaker from getting power in the 'speaker off' position and the other diode is simply there so that the circuitry sees the same voltage in both 'on' positions. Alternately, a switch could be added in series with the speaker to turn it off. After one storm, you will add the switch if you don't include it at first!

3 The basic circuit above is combined with any of the following circuits to complete the lightning detector. The prototype used the 5 volt lamp driver, meter circuit, and speaker circuit. Lamp Circuits The second circuit will drive higher current lamps, up to 500mA. Flashlight bulbs make a bright flash. Meter Circuit The meter sensitivity may be altered by changing the 5.1k resistor.

4 Speaker Circuit No volume control is included but the sound level is not particularly loud. Choose any or all of the above circuits and connect them across the indicated terminals on the basic receiver. An alarm, buzzer, or other load may be activated when the lightning activity exceeds a preset level using the following circuit: A different op-amp or comparator may be used, as long as it is "ground sensing". Look for single-supply types for substitutes. The '339 requires a pull-up resistor on the output but op-amps will not require this part (the 1k resistor). The power supply may be the same 5 volt supply or a different voltage as long as the voltage is within the operating range of the op-amp or comparator. The VMOS transistor may be any type sufficient for driving the load. A VN10KM is a typical part for lower current loads. Add a power switch in series with the load, if desired.

5 5V Power Supply for Lightning Detector Power 9V + Battery 100uF uf + 5 VDC to circuit Gnd External 9VDC Above is an example of a suitable 5V power supply operating from either a 9V battery or an external 9V wall wart power supply. If a higher voltage (eg 12V) is used, a heat-sink is required for the Use a coaxial power jack that switches from battery to external power when the external power is plugged in. Note that many power jacks switch the ground rather than the hot. If you plan on only using the lightning detector while plugged into an AC outlet, then the above power supply is not needed; instead use a regulated 5VDC wall wart connected to the circuit pin out

6 Parts list for basic lightning detector circuit 1 2x3 inch single-hole proto board 1 10 mh choke 1 1 mh choke 2 270K resistor 1 1M resistor 1 10K resistor 1 82K resistor 1 3.9K resistor 1 10pF capacitor 1.001uF capacitor pf capacitor 1 10uF capacitor 1 100uF capacitor 2 2N4401 NPN 1 2N4403 PNP 2 1N914 diode Parts list for light flasher circuit 1 super bright LED 1 1K resistor ohm resistor Parts list for speaker circuit 1 SPST or SPDT switch 1 miniature 16 to 39 ohm speaker 1 150K resistor 1 33K resistor 1 270K resistor pf capacitor 1 0.1uF capacitor 1 100pF capacitor 1 TL431 shunt regulator

7 Parts list for lightning activity meter circuit 1 100uA meter 1 1N914 diode 1 2N4403 PNP 1 1M resistor 1 10M resistor 1 100K resistor 1 5.1K resistor 1 1K resistor 1 47uF capacitor Parts list for power supply V regulator 1 9V battery 1 SPST or SPDT toggle switch 1 100uF capacitor 1 0.1uF capacitor

8 Lightning Detector - modified