AC coupled video signal grounding
day376
Posts: 24
This my first cry for help on the forums, so forgive me if I post wrong.
I am currently in the process of building and interfacing a Closed Captioning Decoder to a basic stamp PX module mounted on a BOE board.· The Closed Captioning Decoder circuit is based on a Microchip PIC16F628A MCU and accepts a composite video output signal from a VCR or TV.· Specific video data·will be·processed and outputted as serial data (to Bspx)·19.2k,8,n,1.·
This is the first time Ive dealt with·AC coupled and DC Restored signals. And my greatest fear is that I have not properly grounded the·coupled AC signal of the·Closed Captioning circuit·and when I connect my cherished BSpx, it'll go up in a cloud of smoke.
I have full confidence that this Closed Captioning circuit works, what I fear is that I have read the circuit design Wrong.· I have included a link to the Closed Captioning Decoder schematic and theory of design.
Closed Captioning Schematic
http://www.brouhaha.com/~eric/pic/caption/ccap628b.pdf
Theory of Design
http://www.brouhaha.com/~eric/pic/caption.html
My questions
This may be a stupid question, but I dont see how the AC coupled video signal, which is fed into the PIC16F628· at PB0(pin6) and the DC Restored Video signal which is fed at PA2 (pin1) can escape through·the video's·AC ground.· Can AC and DC circuits share a common ground node or plane?· And could this seemingly 'lost'·AC coupled signal·harm my new BSpx?·
I've Googled and Asked Jeeves for a week straight for any hints on how to handle this situation with no avail.· Perhaps this is a subject over my head but I've come to far to quit NOW.· I'm not too worried about frying the circuit components, but I MUST draw the line at my BSpx.· My personal circuit has the ground of C9, C10, and R2 going back to Video ground (J2).· The Q1·emitter follower·and R1 are going to the supply ground at (J1).
Is·there any advice or precaution you can offer?
Thanx for anything
Day376
·P.S. Oh and by the way I'm not planning to use the charge pump or the op amp (TLC232) on the right of the schematic when communicating with BSpx, since the PIC's·TX and·DCD·at CMOS level and Rx at TTL.·
I am currently in the process of building and interfacing a Closed Captioning Decoder to a basic stamp PX module mounted on a BOE board.· The Closed Captioning Decoder circuit is based on a Microchip PIC16F628A MCU and accepts a composite video output signal from a VCR or TV.· Specific video data·will be·processed and outputted as serial data (to Bspx)·19.2k,8,n,1.·
This is the first time Ive dealt with·AC coupled and DC Restored signals. And my greatest fear is that I have not properly grounded the·coupled AC signal of the·Closed Captioning circuit·and when I connect my cherished BSpx, it'll go up in a cloud of smoke.
I have full confidence that this Closed Captioning circuit works, what I fear is that I have read the circuit design Wrong.· I have included a link to the Closed Captioning Decoder schematic and theory of design.
Closed Captioning Schematic
http://www.brouhaha.com/~eric/pic/caption/ccap628b.pdf
Theory of Design
http://www.brouhaha.com/~eric/pic/caption.html
My questions
This may be a stupid question, but I dont see how the AC coupled video signal, which is fed into the PIC16F628· at PB0(pin6) and the DC Restored Video signal which is fed at PA2 (pin1) can escape through·the video's·AC ground.· Can AC and DC circuits share a common ground node or plane?· And could this seemingly 'lost'·AC coupled signal·harm my new BSpx?·
I've Googled and Asked Jeeves for a week straight for any hints on how to handle this situation with no avail.· Perhaps this is a subject over my head but I've come to far to quit NOW.· I'm not too worried about frying the circuit components, but I MUST draw the line at my BSpx.· My personal circuit has the ground of C9, C10, and R2 going back to Video ground (J2).· The Q1·emitter follower·and R1 are going to the supply ground at (J1).
Is·there any advice or precaution you can offer?
Thanx for anything
Day376
·P.S. Oh and by the way I'm not planning to use the charge pump or the op amp (TLC232) on the right of the schematic when communicating with BSpx, since the PIC's·TX and·DCD·at CMOS level and Rx at TTL.·