Schematic of FM stereo encoder with discrete components
Xiao Xiao recently discovered an experiment that he once did from old materials. At that time, Xiao Xiao did not have a 38KHZ crystal. Later, I found this picture from a friend. If you are interested, you may wish to try it.
Circuit schematic diagram IC1-4069 Y1, Y2 form an oscillator with a frequency of 76KHZ, after Y3-Y6 isolation and shaping, it is sent to a two-component frequency circuit composed of IC2 double JK trigger CD4027, resulting in a symmetrical +/- 38KHZ And 19KHZ square wave, of which +/- 38KHZ square wave is used to control the IC3 analog switch CD4066, the input stereo audio signal is modulated by the switch and mixed with the 19KHZ frequency signal, and then isolated by the transistor 9014 and sent to the FM modulator . The FM modulator circuit can refer to various FM transmitting circuits in this site. This article is not drawn, the purpose is to make it easy for fans to use this encoder, not only can add stereo function for your previous FM transmission, but also can be used as a general equipment.
Connect the FM modulator and the five-volt power supply according to the figure, and measure the IC1CD4069 pins and IC2 CP, Q, Q, and pins with a multimeter, which should be half of the power supply voltage, indicating that the oscillator has started. If there is a digital frequency meter, measure the output frequency of IC1, adjust RW1 so that the frequency is 75KHZ +/- 10HZ. If not, you can tune the radio first, and then adjust RW1 halfway, then adjust RW1 to make the radio stereo indicator light, and there is no temple howling in the speaker. Then input the stereo audio signal (1.5Vpp, available power amplifier output) from the input terminal, then you can receive the stereo broadcast in the radio. The input signal can also be obtained from the line, but at this time R7 should be changed accordingly. Finally, you can also adjust R7 to minimize high-frequency noise. In fact, R6 and R7 are equivalent to the external components in pins 13 and 14 of BA1404. It is a mixed circuit of pilot signal and composite signal, and then input into the amplifier. It is 9014, and the BA1404 enters from the 12-pin. I think there are many places to be improved in this circuit. If you are interested, you may wish to develop it.
4066 internal block diagram:
4069 internal block diagram:
4027 internal block diagram:
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