Post by thread:[EE]: Detecting Vertical Sync

Hi there. I’m playing around with video and PICs, and I’d like to overlay signals on the video. Question is: How do I detect the VSYNC and if possible HSYNC signals? **** I don’t want to use ICs like LM1881 or EL4581, because I can’t get them at my local electronics store, and I have to order them from somewhere else (and wait!). **** Is there a way of doing that with op-amps or something? All I want is a pulse on the PIC port when VSYNC is present, so I can trigger the software. (BTW, the circuit would be for PAL-N). Hernan Freschi -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

>> Hi there. I'm playing around with video and PICs, and I'd like to overlay signals on the video. Question is: How do I detect the VSYNC and if possible HSYNC signals? **** I don't want to use ICs like LM1881 or EL4581, because I can't get them at my local electronics store, and I have to order them from somewhere else (and wait!). **** Is there a way of doing that with op-amps or something? All I want is a pulse on the PIC port when VSYNC is present, so I can trigger the software. << This is like asking is it possible to heat food without a microwave oven. Early TVs are an existance proof that this can be done with analog electronics without any integrated circuits. You first have to detect Hsync. This is easy as it is the deliberately the most negative point of the waveform. Next low pass filter the Hsync pulses and compare to a threshold. That will be Vsync. The Hsync pulses are stretched during the vertical blanking interval. If you don't want the lag from a low pass filter, just look at the length of Vsync pulses. Hsync starts at the first long Vsync pulse. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On 16 Sep 2002, at 15:05, Olin Lathrop wrote: > This is like asking is it possible to heat food without a microwave oven. > Early TVs are an existance proof that this can be done with analog > electronics without any integrated circuits. > > You first have to detect Hsync. This is easy as it is the deliberately the > most negative point of the waveform. Next low pass filter the Hsync pulses > and compare to a threshold. That will be Vsync. The Hsync pulses are > stretched during the vertical blanking interval. If you don't want the lag > from a low pass filter, just look at the length of Vsync pulses. Hsync > starts at the first long Vsync pulse. > Good reply. I have just had to do something similar with AVR. The pcb was already designed! They just used a LM31x (I forget) comparator with a pot to set the trip level in the centre of the sync pulse. I interrupted on each sync pulse and checked for a timer overflow - the timer is reset for 40uS so you can see if time between sync pulses was more or less than this.. The mark 2 pcb *WILL* use an LM1881 or Elantec equivalent to do the work fom me and remove the preset pot adjustment (user twiddle) problem. George Smith -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Hi Hernan Freschi If you don't want to use the 1881 (great ic!) you could grab a 12C508 and program it for detect the pulses, I think that the best would be something like the 16c621 (they have 2 comparators built in, but are more expensive) the 12C508 are very cheap, and you could make it to detect the vertical and horizontal sync and let you know to a bigger IC via another pin. a good source to figure it out how to do it is looking for the tv decoding cable circuits (a.k.a. "Decos" in my country ;-), those usually detect, using operational amps, the supressed sync of the video encoded signal to lock on, the code is very interesting to take a look, there are over there a lot of that, but you could start looking for the "3chi" code Decos. if they can lock on a supressed sync video signals, do that with a good video signal it's far to easy :-). BTW: if you use Pal-N, are you from Argentina?, if so, did you try to find the LM1881 in GM Electronica or CIKA ?, I usually get this ic from those stores. If you can't find any 3chi code, i can look for it, contact me via private and I'll send you the asm if you need it. good luck Leo At 03:35 PM 9/16/02, you wrote: {Quote hidden}>Hi there. I'm playing around with video and PICs, and I'd like to >overlay signals on the video. >Question is: How do I detect the VSYNC and if possible HSYNC signals? > >**** I don't want to use ICs like LM1881 or EL4581, because I can't get >them at my local electronics store, and I have to order them from >somewhere else (and wait!). **** > >Is there a way of doing that with op-amps or something? All I want is a >pulse on the PIC port when VSYNC is present, so I can trigger the >software. > >(BTW, the circuit would be for PAL-N). > >Hernan Freschi > >-- >http://www.piclist.com hint: The PICList is archived three different >ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Check the schematics on page 6 from this PDF http://www.national.com/ds/LM/LM1881.pdf It is the LM1881 datasheet Francisco Hernan Freschi wrote: {Quote hidden}>Hi there. I m playing around with video and PICs, and I d like to >overlay signals on the video. >Question is: How do I detect the VSYNC and if possible HSYNC signals? > >**** I don t want to use ICs like LM1881 or EL4581, because I can t get >them at my local electronics store, and I have to order them from >somewhere else (and wait!). **** > >Is there a way of doing that with op-amps or something? All I want is a >pulse on the PIC port when VSYNC is present, so I can trigger the >software. > >(BTW, the circuit would be for PAL-N). > >Hernan Freschi > >-- >http://www.piclist.com hint: The PICList is archived three different >ways. See http://www.piclist.com/#archives for details. > > > > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

>Is there a way of doing that with op-amps or something? All I want is a >pulse on the PIC port when VSYNC is present, so I can trigger the >software. Well you should be able to do it in software without too much trouble. You are going to need the HSYNC signal in the PIC anyway, and all you need to do is look for when the pulse has the inverted width to know when you are in the VSYNC time. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

On Mon, 16 Sep 2002 20:41:27 +0100 Geo <.....lintechKILLspam@spam@BLUEYONDER.CO.UK> writes: > On 16 Sep 2002, at 15:05, Olin Lathrop wrote: > > > This is like asking is it possible to heat food without a > microwave oven. > > Early TVs are an existance proof that this can be done with analog > > electronics without any integrated circuits. > > But, you've gotta use vacuum tubes! Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com Reach broadcasters, engineers, manufacturers, compliance labs, and attorneys. Advertise at http://www.hallikainen.com/FccRules/ . ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Well, considering that the microwave IS a vacuum tube (have you ever heard the word MAGNETRON?) -----Mensaje original----- De: pic microcontroller discussion list [.....PICLISTKILLspam.....MITVMA.MIT.EDU] En nombre de Harold M Hallikainen Enviado el: Martes, 17 de Septiembre de 2002 01:22 p.m. Para: EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU Asunto: Re: [EE]: Detecting Vertical Sync On Mon, 16 Sep 2002 20:41:27 +0100 Geo <lintechspam_OUTBLUEYONDER.CO.UK> writes: > On 16 Sep 2002, at 15:05, Olin Lathrop wrote: > > > This is like asking is it possible to heat food without a > microwave oven. > > Early TVs are an existance proof that this can be done with analog > > electronics without any integrated circuits. > > But, you've gotta use vacuum tubes! Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com Reach broadcasters, engineers, manufacturers, compliance labs, and attorneys. Advertise at http://www.hallikainen.com/FccRules/ . ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/web/. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

On Mon, 16 Sep 2002, Geo wrote: *>Good reply. I have just had to do something similar with AVR. The pcb was *>already designed! They just used a LM31x (I forget) comparator with a pot to *>set the trip level in the centre of the sync pulse. I interrupted on each sync Come on, everyone knows about clamping and using the peak rectified voltage from clamping to feed the other side of the comparator. Or amplify the clamped video 8-10 times and feed directly to digital input (clamped 0.3Vpp sync pulses become 0.3*8 = 2.4Vpp pulses and the rest of the picture only raises the voltage more). The amplifier does not need to have video bandwidth. You can use the clamping circuit I sent to the list in a previous thread (using bipolar current mirror as clamp). Peter -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

On 17 Sep 2002, at 1:13, Peter L. Peres wrote: > On Mon, 16 Sep 2002, Geo wrote: > > * The pcb was > *already designed! They just used a LM31x (I forget) comparator with a pot to > *set the trip level in the centre of the sync pulse. > > Come on, everyone knows about clamping and using the peak rectified > voltage from clamping to feed the other side of the comparator. As I said - the pcb was already designed - I was presented with a loaded board to get going. George Smith -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body