OBSTRONICS SYSTEM: CIRCUIT DIAGRAM(1)

The ASIC Transmitter IC has four inputs and only one output pin. The four inputs are for the frequency range of 17 KHz, 19 KHz, 22 KHz and 25 KHz and four switches are provided for each range. When any one switch is selected, that frequency is added to the Transmitter circuit as data frequency and transmitted in the air. The Crystal X1 with two coupling capacitor provides the working oscillator frequency to the circuit. The Capacitors C6 and C7 are to stabilize the crystal oscillator frequency.The ASIC output is added to the transmitter circuit’s oscillator transistor T1s base. The data frequency is added with carrier frequency  147 MHz and aired for transmitting purpose.

The transistor T1 is heart of the Hartely Oscillator and oscillates at carrier frequency of 147 MHz along with tuned circuit formed by coil L1 and capacitor C4. The Data frequency is fed to T1 on base through resistors R4 and R5. Capacitors C1 and C3 and for stabilizing the tuned circuit along with resistor R3To increase the range of the circuit, transmitting signals must be strong enough to travel the long distance [i.e., upto 100 meters in this prototype]. So the generated signals are made strong by amplifying to certain level with the help of Transistor T2 and associated circuit.The Radio frequency thus generated is fed to pre-amplifier transistor T2 on base terminal. The resistor R6 provides the bias voltage to T2 and capacitors C5 & C7 removes the noise and harmonics present in the circuit. The antenna coil L2 transmits the radio frequency in the air.
Fig2Obstronics System With_decrypted
FIG2. CIRCUIT DIAGRAM