spacially distributed feedback
nick bernard
Posts: 329
hail
i'm considering using a shift register to sample a byte of data with my sx28. the register could be up to 500ft away from the sx28. will a sample rate of 1million per second be too high considering the distance of the cable?
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If I lived back in the wild west days, instead of carrying a six-gun in my holster, I'd carry a soldering iron. That way, if some smart-aleck cowboy said something like "Hey, look. He's carrying a soldering iron!" and started laughing, and everybody else started laughing, I could just say, "That's right, it's a soldering iron. The soldering iron of justice." Then everybody would get real quiet and ashamed, because they had made fun of the soldering iron of justice, and I could probably hit them up for a free drink. - Jack Handy
i'm considering using a shift register to sample a byte of data with my sx28. the register could be up to 500ft away from the sx28. will a sample rate of 1million per second be too high considering the distance of the cable?
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If I lived back in the wild west days, instead of carrying a six-gun in my holster, I'd carry a soldering iron. That way, if some smart-aleck cowboy said something like "Hey, look. He's carrying a soldering iron!" and started laughing, and everybody else started laughing, I could just say, "That's right, it's a soldering iron. The soldering iron of justice." Then everybody would get real quiet and ashamed, because they had made fun of the soldering iron of justice, and I could probably hit them up for a free drink. - Jack Handy
Comments
If you mean 1 million samples of 8 bits each, implying 8 megabits/second coming at the SX on a continuous streaming basis, then you might have your hands quite full.
So, it all depends on other things, specifically how you trigger the sample event. Specifically, if the SX is to send out a sample trigger to the remote 500 ft away, that will take about 500 nsec to get there in round numbers. If then the bits are to be clocked from the SX, that clock is also disturbed by a 500 nsec delay. This might be OK, or not, it all depends......
So some more information is required such as the where does the clocking and triggering or framing come from, and is this truly a streaming situation.
Potentially, with some restrictions this is possible. However have you thought of what needs to go on in the SX to deal with such a streaming rate? At 50 MHz that is only 6 instructions per bit.
It CAN get quite complicated, but it might be possible.
Cheers,
Peter (pjv)
Post Edited (pjv) : 7/19/2005 9:15:50 PM GMT
i based the rate on a parrallel project, where ra & rb were the input bytes and no shift registers were needed. the control algorithm is remarkably simple so i was able to get over 1 million samples per sec. 1MSPS is not a programming requirement. adding shift-in routines will lower the sample rate and that is entirely acceptable. i will eventually lower the sample rate to 10-100SPS just to implement a discrete time control algorithm. i just would like to know if the hi frequency of the shifting routine will fail because of the long distances. given the noisey environment and line impedance?
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If I lived back in the wild west days, instead of carrying a six-gun in my holster, I'd carry a soldering iron. That way, if some smart-aleck cowboy said something like "Hey, look. He's carrying a soldering iron!" and started laughing, and everybody else started laughing, I could just say, "That's right, it's a soldering iron. The soldering iron of justice." Then everybody would get real quiet and ashamed, because they had made fun of the soldering iron of justice, and I could probably hit them up for a free drink. - Jack Handy
Other than for purists, practical line impedance is not much of an issue if the transit time for the electrical length is much·less than the shortest pulse duration; at·more than 10 times, I would start to become concerned.
Noise?....... well differential is always good. RS485 can work reliably to 10 Mbits/sec.
So the quick answer; given your relaxation on the constraints, yes this can now readily be done.
Cheers,
Peter (pjv)
Post Edited (pjv) : 7/20/2005 2:53:50 PM GMT
i considered using differentials, i'll research it a little more
rox on
nick
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If I lived back in the wild west days, instead of carrying a six-gun in my holster, I'd carry a soldering iron. That way, if some smart-aleck cowboy said something like "Hey, look. He's carrying a soldering iron!" and started laughing, and everybody else started laughing, I could just say, "That's right, it's a soldering iron. The soldering iron of justice." Then everybody would get real quiet and ashamed, because they had made fun of the soldering iron of justice, and I could probably hit them up for a free drink. - Jack Handy