simmonds@demon.siemens.com (Tom Simmonds) (01/16/90)
I would like to build a circuit to digitize an audio signal, possibly in PCM form, and record it on my VCR, and also to play it back. The video bandwidth should make it easy, but I don't know enough about video signals and VCR's. Does anyone know what I have to do to record a PCM signal on a VCR? Specifically, do I have to add a synch pulse in order to make it record, or can I just take the PCM signal and put it on some carrier frequency (channel 3, for instance) and feed that directly into the VCR without simulating NTSC format? Is there anything, besides the synch pulse, that I have to do to the signal to make it record? Thanks, in advance, for any help you may be able to offer. Please email your response to: simmonds@demon.siemens.com If I get any useful answers, I'll post a summary. ==================================== Tom Simmonds ============================
sorka@ucscb.UCSC.EDU (Alan Waterman) (01/17/90)
Several companies make a product that does what you want. It made vcr's the DAT before DAT.
toddpw@tybalt.caltech.edu (Todd P. Whitesel) (01/18/90)
speaking of which, does anyone know what the restrictions on vcr video signals are? besides sync, is there a voltage limit (i suppose there is one because the line in/out says 1.0v peak-to-peak on everything i have). me and a friend have wondered how tough it would be to record a stream of digital pulses on a vcr tape and play them back (i.e. cheap HD backup, speed doesn't really matter). We tried putting the serial port though an op-amp and recording it on cassette tape, however we had some trouble reading the whole text file back reliably. are there any bizarre restrictions on the inputs to a tape recorder? Todd Whitesel toddpw @ tybalt.caltech.edu
henry@utzoo.uucp (Henry Spencer) (01/19/90)
In article <13400@cit-vax.Caltech.Edu> toddpw@tybalt.caltech.edu (Todd P. Whitesel) writes: >me and a friend have wondered how tough it would be to record a stream of >digital pulses on a vcr tape and play them back (i.e. cheap HD backup, speed >doesn't really matter). We tried putting the serial port though an op-amp >and recording it on cassette tape, however we had some trouble... VCRs are not like audio recorders; they know that their input is a video signal and tinker accordingly. (For example, as I recall, they record sound and picture separately on the tape, meaning they know how to take a video signal apart.) You're going to have to make your digital data look like video, at least to the extent of having sync pulses, I'd guess. -- 1972: Saturn V #15 flight-ready| Henry Spencer at U of Toronto Zoology 1990: birds nesting in engines | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
phupp@warwick.ac.uk (S Millington) (01/19/90)
Devices which provide HD backup on standard VCR's are available, in the UK at least - I think I also saw an add in Byte so probably in the US aswell. As far as I remember they put a few hundred megabytes on a short tape and cost about 200 pounds. Unfortunately the only versions I've seen were with PC Card interfaces. Stuart Millington. phupp@poppy.
maj@hpfinote.HP.COM (Mike Jassowski) (01/20/90)
/ hpfinote:sci.electronics / henry@utzoo.uucp (Henry Spencer) / 9:46 am Jan 18, 1990 / >In article <13400@cit-vax.Caltech.Edu> toddpw@tybalt.caltech.edu (Todd P. Whitesel) writes: >>me and a friend have wondered how tough it would be to record a stream of >>digital pulses on a vcr tape and play them back (i.e. cheap HD backup, speed >>doesn't really matter). We tried putting the serial port though an op-amp >>and recording it on cassette tape, however we had some trouble... I had some luck recording digital on audio tapes. I had to modulate the digital information. Audio recorders have trouble with DC; if you have several ones/zeros in a row, it starts to look like DC. A little filtering the output restored the informtion. > >VCRs are not like audio recorders; they know that their input is a video >signal and tinker accordingly. (For example, as I recall, they record sound >and picture separately on the tape, meaning they know how to take a video >signal apart.) You're going to have to make your digital data look like >video, at least to the extent of having sync pulses, I'd guess. Most VCRs have separate "video in" and "audio in" ports, as well as the RF connection. If you used these, there may be less artificial video stuff that needs to be done. My thesis advisor claimed that an audio type signal into the video port should work, but you would still have to modulate any digital information (although I never tried it). To give this a try, you might just attempt an audio recording through the video input, and see if it is distorted on playback. >-- >1972: Saturn V #15 flight-ready| Henry Spencer at U of Toronto Zoology >1990: birds nesting in engines | uunet!attcan!utzoo!henry henry@zoo.toronto.edu ----------
john@frog.UUCP (John Woods) (01/20/90)
In article <1990Jan18.164648.15896@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: > VCRs are not like audio recorders; they know that their input is a video > signal and tinker accordingly. (For example, as I recall, they record sound > and picture separately on the tape, meaning they know how to take a video > signal apart.) You're going to have to make your digital data look like > video, at least to the extent of having sync pulses, I'd guess. As I understand it, this is roughly how it *is* done: you make a TV picture where the image is something that you can tear apart digitally (shades of the old CRT computer memories !-) For a while, WGBX TV Boston was running an experimental encoding system where they would transmit digital audio in the picture frames, with the audio from WGBH FM for reference in the audio channel. You could actually SEE the bits. Very entertaining watching (for a few seconds anyway). -- John Woods, Charles River Data Systems, Framingham MA, (508) 626-1101 ...!decvax!frog!john, john@frog.UUCP, ...!mit-eddie!jfw, jfw@eddie.mit.edu Happiness is Planet Earth in your rear-view mirror. - Sam Hurt
wiml@blake.acs.washington.edu (William Lewis) (01/30/90)
On the subject of recording info onto an audio tape, has anyone tried using a modem to recored onto a cassette? My "original Hayes" had some pretty odd commands, designed for use in radioteletype and such, that should make it quite easy to do this. (Alas, my newer modem has twice the speed but 1/100 the nifty options. "Hayes compatible", my foot. Did you know a Hayes has special commands for sending Morse code?) On the other hand, modems are designed for the comparitively narrow bandwidth of a phone line, so it should be possible to get higher data rates on a VCR tape, even without all the fancy 0.0001 degree phase encoding ... -- wiml@blake.acs.washington.edu (206)526-5885 Seattle, Washington
strong@tc.fluke.COM (Norm Strong) (01/31/90)
In article <15880005@hpfinote.HP.COM> maj@hpfinote.HP.COM (Mike Jassowski) writes: }/ hpfinote:sci.electronics / henry@utzoo.uucp (Henry Spencer) / 9:46 am Jan 18, 1990 / }>In article <13400@cit-vax.Caltech.Edu> toddpw@tybalt.caltech.edu (Todd P. Whitesel) writes: }>>me and a friend have wondered how tough it would be to record a stream of }>>digital pulses on a vcr tape and play them back (i.e. cheap HD backup, speed }>>doesn't really matter). We tried putting the serial port though an op-amp }>>and recording it on cassette tape, however we had some trouble... } }I had some luck recording digital on audio tapes. I had to modulate the }digital information. Audio recorders have trouble with DC; if you have }several ones/zeros in a row, it starts to look like DC. A little filtering }the output restored the informtion. }> }>VCRs are not like audio recorders; they know that their input is a video }>signal and tinker accordingly. (For example, as I recall, they record sound You could buy a Toshiba DX-900. It has built in digital audio capability. -- Norm (strong@tc.fluke.com)
annala@neuro.usc.edu (A J Annala) (02/11/90)
In article <13400@cit-vax.Caltech.Edu> toddpw@tybalt.caltech.edu (Todd P. Whitesel) writes: > >me and a friend have wondered how tough it would be to record a stream of >digital pulses on a vcr tape and play them back (i.e. cheap HD backup, speed >doesn't really matter). I have an eight channel sequentially multiplexed analog-to-digital converter in my lab hooked up to a SONY PCM-F1 digital audio signal processor. This unit converts 16 bit ADC samples at 88.2 KHz and stores them on just about any cheap commercially available low end consumer grade VCR. It works just as well in extended play mode as it does at higher speeds. The SONY PCM-F1 generates a standard digital recording format called EIAJ PCM. The trouble comes when you try to hook this device up to an IBM PC/AT. My simple minded 16 bit wide synchronously clocked digital input board talks to channel 6 of the second 8237A DMA chip just fine. However, I am unable to write any data to the hard disk (via turbo/microsoft c io library calls, msdos file services, or direct calls to the hard disk read/write bios ints. Does anyone have a clue why a DMA interface accepting 16 bit wide data at 88.1 KHz would interfere with access to my hard disk? Does the controller for the hard disk assume no dma cycles are present on the bus while it is trying to write data to the disk? Is there any solution that would allow simultaneous DMA input and file oriented or raw hard disk output? The only solution I have at the moment is to build a buffered digital interface containing a FIFO chip (IDT7202 -- any know what this is -- where to buy a few of them -- where to get a spec sheet -- how large a buffer memory is available) that will hold data while I mask (disable) DMA input long enough to write to my hard disk. This buffering scheme was presented (but only briefly discussed) in Dr. Dobb's Journal Jan90 pp. 28-37, pp.94-95 with a hardware outline and supporting MSC5 code. Does anyone make clocked digital input boards with large fifo buffers for commercial purchase? Thanks, AJ Annala, USC Neuroscience Program, HNB-534A, LA, CA 90089-2520 Telephone: (213)743-3251 (office) (213)743-8868 (lab) ------------------------------------------------------------------------- For further information on constructing multi channel analog/digital to VCR adaptors the following articles are quite helpful and detailed: Bezanilla, Francisco. A high capacity data recording device based on a digital audio processor and a video cassette recorder. Biophys. J. 47:437-442 (1985). Lamb, T. D. An inexpensive digital tape recorder suitable for neurophysiological signals. Journal of Neuroscience Methods 15:1-13 (1985). Chiang, R. G. et al. Recording electrophysiological data on video tape: a superior and less costly alternative to conventional tape recorders. Journal of Neuroscience Methods 15:15-20 (1985). Blaettler, Markus et al. Data recording and playback on video tape -- a multi-channel analog interface for a digital audio processor system. J. Neuroscience Methods 23:139-148 (1988). These systems are also available commercially from a number of sources. Medical Systems Corp, One Plaza Road, Greenvale, NY 11548 (516)621-9190. Vetter Instruments ... your neuroscience people get advertisements from these people all of the time ... some of their adaptors are just simple FM modulated carriers representing analog signals on modified VCR's ... other adaptors are analog to digital --> multiplexed --> digital to PCM --> recorded as bright spots on VCR.