Sajjad,

Tuner in satellite receivers are equipped with built in PLL ic usually
5511 from philips. Micro controller can communicate with tuner thru I2C
bus to select the frequency desired. 5511 also has a built in ADC for
auto scanning, where mcu programs tuner PLL from starting and read back
the ADC output thru I2C bus and decides when a valid channel is found.

Motor used in polariser is not the stepper motor. The motor reuires
continous 5 V pulses. The motor position is decided by the pulse
width/duty cycle.

I have programmed mcu's for commercial receiver and can provide more
details, if required.


Vinay Chaddha


Sajjad.akhtar wrote:
>
>
>      Last weakened my bro showed me a little circuit that was to control
>      the polarize in the LNB and tuner in the dish receiving unit.
>
>      That was equipped with a microcontroler 8051. I am interested in
>      building my own. But i dont know how servo moter in polarizer is
>      controled and what sort of signal is used to control the tuner circut.
>      (Same tuner comes in many dishreciever circut like winer sat etc)
>      I was asuming that signal should be of analog but both the digitizer's
>      servo motor and tuner were directly controled from the microcontroler
>      output (no capacitors for pwm ... DAC) and that version of 8051 doesnt
>      contians any DAC.
>
>      This means they were using digital signal. Can any one help me that
>      what kind of signals both the units uses.
>
>