FM Telephone Bug

Description:

Here is a simple transmitter that when connected to a phone line, will transmit anything on that line (execpt the dial tone) to any FM radio. The frequency can be tuned from 88 to about 94Mhz and the range is about 200 feet. It is extremely easy to build and is therefore a good, useful beginner project.

Notes:

1. L1 is 7 turns of 22 AWG wire wound on a 9/64 drill bit. You may need to experiment with the number of turns.

2. By stretching and compressing the coils of L1, you can change the frequency of the transmitter. The min frequency is about 88 Mhz, while the max frequency is around 94 Mhz.

3. The green wire from the phone line goes to IN1. The red wire from the phone line goes to IN2. The green wire from OUT1 goes to the phone(s), as well as the red wire from OUT2.

4. The antenna is a piece of thin (22 AWG) wire about 5 inches long.

5. All capacitors are rated for 250V or greater.

6. The transmitter is powered by the phone line and is on only when the phone is in use. S1 can be used to turn the transmitter off if it is not needed.

7. If you have problems with the LED burning out, then add a 300 ohm 1/4W resistor in series with it.

Parts:

Part Total Qty. Description
R1 1 180 Ohm 1/4 W Resistor
R2 1 12K 1/4 W Resistor
C1 1 330pF Capacitor
C2 1 12pF Capacitor
C3 1 471pF Capacitor
C4 1 22pF Capacitor
Q1 1 2SA933 Transistor
D1,D2,D3,D4 4 1SS119 Silicon Diode
D5 1 Red LED
S1 1 SPDT Switch
L1 1 Tuning Coil
MISC 1 Wire, Circuit Board

7 Segment LED Counter

This simple counter can be used to count pulses, as the basis for a customer counter (like you see at the doors of some stores), or for anything else that may be counted. The circuit accepts any TTL compatible logic signal, and can be expanded easily.

Schematic

7 Segment Display Reference

Parts:

Part	Total Qty.	Description	Substitutions
R1-R7	7	470 Ohm 1/4 Watt Resistor
U1	1	74LS90 TTL BCD Counter IC	7490,74HC90
U2	1	74LS47 TTL Seven Segment Display Driver IC	7447,74HC47
DISP1	1	Common Anode 7 Segment LED Display
MISC	1	Board, Sockets For ICs, Wire

1. All pulses to be counted are to be TTL compatible. They should not exeed 5V and not fall below ground.

2. You can add more digits by building a second (or third, or fourth, etc...) circuit and connecting the pin 11-6 junction of the 74LS90 and 74LS47 to pin 14 of the 74LS90 in the other circuit. You can keep expanding this way to as many digits as you want.