Touch Switch Circuit

Describe:
This circuit uses a 555 timer as the bases of the touch switch. You can learn more about 555 timers in the Learning section on my site. When the plate is touched the 555 timer is triggered and the output on pin 3 goes high turning on the LED and the buzzer for a certain period of time. The time that the LED and the buzzer is on is based on the values of the capacitor and resistor connected to pin 6 & 7. The 10M resistor on pin 2 causes the the circuit to be very sensitive to the touch.

4 Transistors Tracking Transmitter

DESCRIPTION:

This tracker works with your regular AM/FM radio or car stereo. Car stereo would be best because it is designed to perform optimum in all conditions.

Real distance is unknown at this time because I never measured it accurately but guess about 300 feet (100 meters). The reception of the signal also depends on the surroundings like tall buildings etc. Most likely the best performance is optained with line-of-sight.

If you can somehow use a longer antenna and beef up the supply voltage to 12V, the performance will be a lot better, just make sure the electrolytic capacitors have the correct working voltage (25V) 1/8" (" = inch) is approximately 3.5mm. 22 ga (USA gauge) is approximately 1.5mm. Antenna: 10 - 12" is approximately 25 to 30cm. A "Non-conductive" core means: wooden dowel, plastic, paper, etc.

47K means 47,000 ohms. The 'K' stands for '1000'. C2/C5: .001uF is the same as 0.001uF or 10nF (nanoFarad). A 'trimmer' capacitor (C3) is an adjustable air capacitor (available everywhere).

The 'ground' symbol shown at the end of Q2's emitter (e) is the negative side of the battery supply.

This circuit belonged to the collection of Art Swan's "Circuit Land".

Sun-Up Alarm

The Sun-Up Alarm can be used to provide a audible alarm for when the sun comes up or it can be used in a dark area and detect when a light comes on. It can also be used to detect a light beam, headlights etc. The circuit works as follows. The phototransistor is very sensitive to light. (Any phototransistor will work fine) The sun shining on this device will provide a high to one of the NAND gates. This will cause another NAND gate to oscillate which will drive another gate to output a 100hz tone. The transistor provides drive for the speaker.

IR Remote Control Jammer

Description:
Don't like your little brother's TV channel selection? Hate the volume your wife sets the stereo at? Want to just annoy someone? This circuit does all that and more by jamming most IR remote signals. The circuit releases a flood of pulsing IR light that confuses the reciever by corrupting the data stream.
Notes:
You may need to adjust the value of R3 for the right frequency. A pot can be used.
You may only need one IR LED.
It goes without saying that this circuit should be used with descretion.
The value of R5 depends on your supply voltage and LED. For a standard 4.5V supply and standard IR LED, use 22 Ohm as specified on the parts list.

AM reciever

Description:
This is a compact three transistor, regenerative receiver with fixed feedback.
It is similar in principle to the ZN414 radio IC which is now no longer available. The design is simple and sensitivity and selectivity of the receiver are good.

Notes: All general purpose transistors should work in this circuit, I used three BC109C transistors in my prototype.The tuned circuit is designed for medium wave. I used a ferrite rod and tuning capacitor from an old radio which tuned from approximately 550 - 1600kHz. Q1 and Q2 form a compund transistor pair featuring high gain and very high input impedance. This is necessary so as not to unduly load the tank circuit.

The 120k resistor provides regenerative feedback,between Q2 output and the tank circuit input and its value affects the overall performance of the whole circuit. Too much feedback and the circuit will become unstable producing a "howling sound". Insufficient feedback and the receiver
becomes "deaf". If the circuit oscillates,then R1's value may be decreased; try 68k. If there is a lack of sensitivity, then try increasing R1 to around 150k. R1 could also be replaced by a fixed
resisor say 33k and a preset resistor of 100k. This will give adjustment of sensitivity and
selectivity of the receiver.

Transistor Q3 has a dual purpose; it performs demodulation of the RF carrier whilst at the same time, amplifying the audio signal. Audio level varies on the strength of the received station but I had typically 10-40 mV.
This will directly drive high impedance headphones or can be fed into a suitable amplifier.

Construction:
All connections should be short, a veroboard or tagstrip layout are suitable. The tuning capacitor has fixed and moving plates. The moving plates should be connected to the "cold" end of the
tank circuit, this is the base of Q1, and the fixed plates to the "hot end" of the coil, the juction of
R1 and C1. If connections on the capacitor are reversed, then moving your hand near the capacitor will cause unwanted stability and oscillation.

Finally here are some voltage checks from my breadboard prototype. This should help in determining a working circuit:-
All measurements made with a fresh 9volt battery and three BC109C transistors with respect to the battery negative terminal.
Q1 (b) 1.31V
Q2 (b) 0.71V
Q2 (c) 1.34V
Q3 (b) 0.62V
Q3 (c) 3.87V