On Thu, 18 Sep 1997 08:07:52 -0500 GERALD LEWIS writes: > I want to use a VCR to record audio only. However, the audio >track > will not record unless a baseband video signal is present. It >does not > have to be modulated. Does anyone know of a source for a >portable > baseband sync generator. I do not have the time to build one. > > Tnx. Gerald Lewis > Most VCR's of the "hi-fi" (not "HQ") type have a circuit which allows them to record audio only. Of course you want to use a hi-fi VCR anyway since the audio quality is much higher. The one I have also has a switch that lets you take video from the tuner and audio from the line inputs. So you could tune in a strong TV station for the video reference. VCRs that don't have a "Input : Tuner/Line" switch on the panel usually have the switch in the input jacks. When a plug is inserted, the tuner is switched off and the line input becomes active. Possibly just plugging in the audio cable but not the video will let you use video from a TV station along with external audio. Exhausting these possibilites, the quickest way to improvise a sync generator from mass-market items would be an inexpensive CCD camera and some black tape (for the lens). As for hommemade there is an old RCA CMOS chip designed to do exactly this but it is somewhat expensive. It would also be a not too complicated PIC project. The NTSC horizontal rate is 4.5 MHz / 286. This video signal would be somewhat nonstandard since you'd be using the color frequency but not transmitting any color bursts. This is how many B&W movies were broadcast (back when there was such a notion as broadcasting a B&W movie) so VCR's should accept it. Unfortuantely 286 / 4 = 71.5 so a 9 or 18 MHz PIC crystal would be needed to make the frequency come out to an integer number of PIC instructions. The 18 MHz frequency seems to be most readily available, but it is too fast for a 16X84. Of course a VCR would lock to frequencies that are a little off so uisng whatever crystal you have and the closest integer would likely do.