mark Posted July 29, 2005 Report Share Posted July 29, 2005 Hi we would like to ask if it is right to use frequency to voltage converter to be connected to the AGC circuit of TV and the output of that converter will be connected to A/D converter before interfacing to microcontroller? the purpose of frequency to voltage converter is to convert the frequency coming from the AGC circuit of the TV to voltage signal. thanks we are hoping for your response Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 29, 2005 Report Share Posted July 29, 2005 Hi Mark,The AGC circuit of a TV controls its gain (Automatic Gain Control). It is well-filtered so that it doesn't have any AC signal which would modulate the picture. Therefore it doesn't have a frequency, just a DC voltage that varies with RF signal strength.What is your microcontroller going to do in a TV? ??? Quote Link to comment Share on other sites More sharing options...
mark Posted July 30, 2005 Author Report Share Posted July 30, 2005 hi, You mean it is unnecessary to place a frequency to voltage converter? The microcontroller will serve as a driver for "automatic positioning of antenna"... Our project is all about signal sensing antenna which automatically rotates and select for proper angle to where the signal is strength. Then after positioning the antenna, the channel frequency, channel number, and power output of each TV stattion will be displayed on the LCD. Another part of the design which makes it difficult to us is the communication between the microcontroller and TV... the microcontroller must determined the the selected channel so that it can display it to the LCD.we would like to ask to your opinion about this subject... Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 30, 2005 Report Share Posted July 30, 2005 You mean it is unnecessary to place a frequency to voltage converter?That's correct. AGC is a DC voltage, not a frequency. But it is more complicated because there is one AGC voltage for a TV's IF amplifier that stops at a certain high level, then a 2nd AGC voltage takes over to feed the tuner for higher levels. The AGC voltages might have opposite polarities and voltage ranges.The microcontroller will serve as a driver for "automatic positioning of antenna"... Our project is all about signal sensing antenna which automatically rotates and select for proper angle to where the signal is strength. Then after positioning the antenna, the channel frequency, channel number, and power output of each TV stattion will be displayed on the LCD. Another part of the design which makes it difficult to us is the communication between the microcontroller and TV... the microcontroller must determined the the selected channel so that it can display it to the LCD.we would like to ask to your opinion about this subject...Good luck. 8)All TV models use different circuitry. Maybe you should have a 2nd identical TV as backup, in case the 1st one fails.I hope you finish your project before antennas there become obsolete. Cable and satellite TV here is so popular that almost nobody uses an antenna anymore. ;DAbout 40 years ago I had a very high gain TV antenna with a rotator. I could get up to 3 distant stations on the same channel from their 3 different directions. The antenna had a very narrow angle for best reception but the rotator was accurate and repeatable so after tuning each channel accurately only 1 time, I marked its dial and reception was fine unless a tall building got built near me.I had best reception of some local channels from reflection from buildings. ;D Quote Link to comment Share on other sites More sharing options...
mark Posted August 3, 2005 Author Report Share Posted August 3, 2005 hi sir! Quote Link to comment Share on other sites More sharing options...
mark Posted August 3, 2005 Author Report Share Posted August 3, 2005 hi sir! Thanks for your reply, can i get your email address so that i could send to you a copy of our system block diagram? and if you dont mind please help us correct our system diagram.. Together with the diagram we will have a brief discussion regarding this... Also, i would like to ask if the Tuner circuit of TV will be advisable to use so that the channel can be display on the LCD.... What we are going to do is to top some wire to the output of the tuner of TV and that output will be connected to the frequency to voltage converter and obviously the output is voltage then connected again to A/D converter so that the microcontroller can interpret the selected channel. is it correct? here's what i want to say........tuner circuit of TV ===> freq to voltage converter ===> A/D converter ==> microcontroller since the tuner circuit selects the desired station and reject the unselected station.. we decided to get its output so that the microcontroller can determined the selected station. Quote Link to comment Share on other sites More sharing options...
elect Posted August 3, 2005 Report Share Posted August 3, 2005 Hi to all..Mark, can U atach a jpg. block diagram of your project in the next reply. I am confused about your ambition... And interest too. Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 3, 2005 Report Share Posted August 3, 2005 What we are going to do is to top some wire to the output of the tuner of TV and that output will be connected to the frequency to voltage converter and obviously the output is voltage then connected again to A/D converter so that the microcontroller can interpret the selected channel. is it correct? here's what i want to say........tuner circuit of TV ===> freq to voltage converter ===> A/D converter ==> microcontroller Quote Link to comment Share on other sites More sharing options...
elect Posted August 3, 2005 Report Share Posted August 3, 2005 4 audioguru:How is modulated video signal. Can U atach a grafics if U have some. Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 3, 2005 Report Share Posted August 3, 2005 Hi DR,TV in North America has its luminance (brightness) single-sidband amplitude-modulated with a small vestigial sideband. Its colour is red and blue quadrature phase-modulated 3.79159Mhz higher and the sound is frequency-modulated 4.5MHz higher.The picture is vertically interlaced and each half-frame's frequency is slightly less than 60Hz, and the horizontal scan rate is slightly less thn 15,750Hz.Whew. I haven't talked about this stuff for about 40 years.A graph of luminance and audio carriers is here: Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 3, 2005 Report Share Posted August 3, 2005 OOps, I forgot. :-[The colour quadrature phase modulated carrier is suppressed, and a 9-cycle burst of its carrier is added to the back porch of the horizontal sync pulse to sync the colour TV's colour demodulator. ;D Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted August 4, 2005 Report Share Posted August 4, 2005 Since you've used a Howstuffworks graphic it'd be only right to link the article. ;D Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 4, 2005 Report Share Posted August 4, 2005 Hi Alun,I didn't link to the article 'cause it talks more about our vision and CRT's and not much about modulation nor how TV's actually work.I wanted to link to the application note from National Semi in their Analog Handbook called "A color TV primer for engineers" but couldn't find it on their website. ;D Quote Link to comment Share on other sites More sharing options...
elect Posted August 4, 2005 Report Share Posted August 4, 2005 Thank U Audioguru... Thank's Alun too, but I have allredy red the artical in HowStuffWorks, but I didn't faund all what I am looking for. Now, when I know how is modulated video signal, can someone tell me how video signal look's in function of time, V=f(t)? For adequate anology U can use audio signal. - Audio signal is like alterning nonharmonic voltage.Is video signal have same shape???What is a frequency range of visible video signal, but not in microwave form (like light), then in transformed (by a camera) voltage form??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 4, 2005 Report Share Posted August 4, 2005 A video signal is made of individual horizontal lines of video, followed by a horizontal sync pulse, then another line of video followed by another sync pulse etc for about 262.5 lines in North America, then the horizontal sync pulses are modified to produce a vertical sync pulse.Audio is completely different since it is continuous without sync pulses.The frequency range from a video camera is about 60MHz, about the same as your computer monitor, but is reduced to about 4MHz for broadcasting over ordinary television. The frequency range broadcast for High Definition TV is about 20MHz. Quote Link to comment Share on other sites More sharing options...
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