“51 High-tech practical jokes for the Evil Genius” written by Brad Graham and Kathy McGowan is one of the multiples books that we can find inside the “Evil Genius collection” dedicated to electronic circuits, schematics and learning.
As the title shows, this one is dedicated to practical jokes which believe me, some can be very funny, some others are pretty scaaary and others can be really painful!…jjj
Evil Genius has a long collection of pdf related to sciences, knowledge and practical projects documented achieving theoric and practical aspects and focused on the learning by doing, that will make your learn fast, accurate and having some fun.
Just be careful, cause some pdf of this collection are out-of-time such as the Spy Gadgets pdf where they use VHS to develop a video project. :SS
For this time I wanted to leave here the schematics from Voices from the Grave circuit found in the pdf up here. (project 22)
This device is supposed to scare all your visitors, friends and w/e cause from any sound source , mp3, radio, or microphone … will generate a scary and horrible noise that will sound just as if the sound was coming from hell, as if the voice talking was from 15 feet under.
So, the responsible to produce this effect is that the signal is carried on a beam of weak infrared light and detected by a phototransistor in the receiver circuit producing that the received audio will seem to fade in and out with a ghostly static.
In this device, we will have 2 circuits that use the same IC (LM386 integrated circuit) both working with 9V batteries power supply.
TRANSMITTER (that has an audio input and takes sound from a mp3 source, and that has an infrared led as output)
The 100ohm resistor can also be swapped for a lower value between 10 & 50 ohms if you want to try pumping up the output from the infrared led. This circuit is so easy that I did not use a circuit board, I just soldered them directly. If you do so, add a bit of hot glue to the components after the unit has been tested.
RECEIVER (that has a phototransistor as input that detects the modulated signal sent by the transmitter and amplifies the signal having as an output a jack or minijack end.)
The output signal sent by the infrared led in the transmitter circuit is detected by a NPN Phototransistor becoming the modulated voltage for the input in the receiver circuit. Doesn’t matter which type, just a standard one. The 10microF capacitor can be removed from the circuit or added to a switch if you find that the receiver’s output is too loud, as this controls the gain of the amplifier. You can also add a 50Kohm potentiometer soldered in series with one of the headphone wires that will become the volume control.
Because of the extreme sensitivity of the phototrans to any light changes, the unit will also pick up all ambient light sources resulting in some ghostly crazy sounds.
LM386 pin-out: (always check on the datasheet)
LM386 is an op amp that can amplify signal input til a gain of 200 if we connect some components around it. Internally has a gain of 20 already, but we can stronger its capacity by building this next schematic circuit down here:
Other posible (between many) circuit to build with LM386 is a Low Distorsion Power Wienbridge Oscillator:
And last but not least: A square wave oscillator:
Here is a pdf to play with: http://www.nari.ee.ethz.ch/wireless/education/PPS/PPS02/doc/LM386.pdf