I want to tune the TV tuner/ 89C52 project

[Madanlov]

Hello

I need to tune the channels using 89c52. The tuner needs 0 to 33 volts, and steps should be very fine (in some milivolts) I believe.

Have tried 16 bit ADC but results are poor. All the channels cant' be tuned.

Can anyone help:?:

I checked up in the TV, which uses Phillips TV processor. That processor used some intelligent algorithm and generates complicated PWM. Works marvellous.

I tried to write the software to generate the waveform. But the execution time required is high even after running the 89C51 at 40MHz.

Thanks
Madan

 

[Nigel Goodwin]

Hello

I need to tune the channels using 89c52. The tuner needs 0 to 33 volts, and steps should be very fine (in some milivolts) I believe.

Have tried 16 bit ADC but results are poor. All the channels cant' be tuned.

Can anyone help:?:

I checked up in the TV, which uses Phillips TV processor. That processor used some intelligent algorithm and generates complicated PWM. Works marvellous.

I tried to write the software to generate the waveform. But the execution time required is high even after running the 89C51 at 40MHz.

Thanks
Madan

As you say, TV tuners are usually fed from a PWM output followed by filtering, I suspect this is a hardware feature of the chips - which are specifically designed for TV use.

Does your processor have any hardware PWM channels?. If so you could try two of them, one for coarse tuning and one for fine tuning. Sum the outputs together using an opamp adder - with the fine tuning input having less gain (obviously) - effectively doubling your resolution.

You could try monitoring the existing TV tuning voltage while you fine tune, that way you can find the actual steps required.

 

[Madanlov]

Thanks.

I would try that. Yeah the PWM generated is from TV processor IC specifically designed for TV. Also, the type of pulses are totally different from traditional PWM.

It's difficult to explain, in words. I would probably draw it and scan the image and post.

On the processor, I dont have any PWM channels. Otherwise it would have been simple.

regards
madan

 

[Matt(Pic progger)]

:idea:

Maybe you can use a 12f675 or similar to generate the pwm, as a stand alone chip. Talk to this via you existing control PIC....

Just an idea.....

 

[Nigel Goodwin]

Thanks.

I would try that. Yeah the PWM generated is from TV processor IC specifically designed for TV. Also, the type of pulses are totally different from traditional PWM.

It's difficult to explain, in words. I would probably draw it and scan the image and post.

All the TV's I've looked at (which use this type of tuning) use standard PWM out of the processor - I've scoped quite a few over the years, when looking for tuning faults. Most modern TV's now use digital tuning, with the tuning voltage generated inside the tuner PLL and controlled by an I2C bus.