Light intensity wireless measurement FM transmitter circuit analysis

The machine first transmits the light intensity change signal after awakening the high frequency FM modulation and multiplying the frequency. By accepting this signal, an FM receiver (FM radio) can be used, and then a side frequency circuit is used to obtain a frequency display signal reflecting the light intensity.
The circuit is shown in Figure 17.7, the photodiode when PD. The 7555 constitutes a light control frequency oscillator. 2833 is an FM high-frequency transmitting circuit with internal audio limit amplification, FM reactance modulation high-frequency oscillation, and frequency multiplying amplifier circuit.
Light enhancement causes a change in PD current, causing the 7555 oscillation frequency to vary from 100 Hz to 5 kHz. This oscillation signal is sent to the 5833 pin 5, first through the limiting amplification, 10kΩ potentiometer amplitude adjustment, enter the 3 feet to complete the FM modulation, from the 14th foot to the 13th foot to 6 times the frequency amplification, into the 8th foot After further amplification, a 98 MHz FM signal is output from the 9th pin.
There are two tuning loops, all of which need to be tuned at 98MHz. Both can be wound with the same miniature high-frequency magnetic core frame and around 0.12mm. The B1 primary is wound around 10 turns and the secondary is wound around 3 turns. The B2 primary is wound around 10 turns and the secondary is wound around 7 turns. L can be adjusted with the same magnetic core skeleton with a 0.1mm enameled wire around 30匝, with a crystal of 16.605MHz.
The power supply voltage ranges from 3 to 9V, and the total current consumption is within 10mA. It can be supplied with battery. The current consumption of the 7555 and 2833 is about 3 mA each.