88 108 mhz pll controller for fm

Posted on Feb 7, 2014

This circuit will explain the PLL controller unit for the FM transmitter. It is very important since the transmitter frequency is digitally controlled and thereby very stable. The heart of this unit is a PIC processor called PIC16F870, a 2 x 16 char display and four buttons. If jumper J1 is disconnected the LCD will have soft backlight because a l

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ow current will pass through R6. If jumper J1 is connected you will have strong backlight. The component are not critial at all, the Pot (P1) can be from 1k-22k and (R1-R5) resistor can be changed to 1k-10k. The orange squars are the input from the buttons to select frequencies. The green squars are connection to the PLL at the VCO. The display has 2 lines with 16 Chars. The first line of the display show "FM Radio station", next line will show the frequency. If you want, you can write your own text on the first line. To modify the test, you press Inc 50 kHz button or Dec 50kHz button during power up. You can change the chars up/down with the two buttons. When you find thechar you like you press Inc 1Mhz button to go to next char. When all 16 Char is entered, the unit restart with the new text.

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