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#1
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Pretty accurate zero-crossing detector, just for fun.
Needs a little work, but the concept is that the mains is full-wave
rectified and compared with a reference. On the downward slope, when the mains-derived signal crosses the reference, the counters are enabled and a single RESET pulse generated and sent to the up counter, clearing it. It then counts clocks until the mains derived signal goes to zero and starts rising again, and when it crosses the reference this time the counters are disabled and a single pulse generated which broadside loads the Q outputs of the up counter into the D inputs of the down counter, but shifted one bit to the right, (MSB to the left) with the result being that a quantity with a magnitude half that of the up counters contents will be loaded into the down counter. Now, when the mains signal peaks and starts falling again, it will again intercept the reference. When it does, the counters will be enabled, the up counter will be cleared and will start incrementing again, and the down counter will start decrementing until it gets to zero, when a single pulse will be generated. Since the quantity loaded into the down counter was half of the quantity accumulated by the up counter between the two excursions across the reference, then it would take the down counter half that time to time out, and the pulse generated at timeout should be located precisely at the zero crossings of the mains cycles. Well, within 10 microseconds anyway... :-) It takes a few minutes for the sim to run, but I think you'll enjoy it. :-) BTW, copy all the files into a single folder and then click on the ..asc file to run it. LTspice should find it and launch it. -- JF |
#2
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Pretty accurate zero-crossing detector, just for fun.
On Thu, 23 Feb 2012 15:52:38 -0600, John Fields wrote:
Needs a little work, but the concept is that the mains is full-wave rectified and compared with a reference. On the downward slope, when the mains-derived signal crosses the reference, the counters are enabled and a single RESET pulse generated and sent to the up counter, clearing it. It then counts clocks until the mains derived signal goes to zero and starts rising again, and when it crosses the reference this time the counters are disabled and a single pulse generated which broadside loads the Q outputs of the up counter into the D inputs of the down counter, but shifted one bit to the right, (MSB to the left) with the result being that a quantity with a magnitude half that of the up counters contents will be loaded into the down counter. Now, when the mains signal peaks and starts falling again, it will again intercept the reference. When it does, the counters will be enabled, the up counter will be cleared and will start incrementing again, and the down counter will start decrementing until it gets to zero, when a single pulse will be generated. Since the quantity loaded into the down counter was half of the quantity accumulated by the up counter between the two excursions across the reference, then it would take the down counter half that time to time out, and the pulse generated at timeout should be located precisely at the zero crossings of the mains cycles. Well, within 10 microseconds anyway... :-) It takes a few minutes for the sim to run, but I think you'll enjoy it. :-) BTW, copy all the files into a single folder and then click on the .asc file to run it. LTspice should find it and launch it. Three phase? Grant. |
#3
Posted to alt.binaries.schematics.electronic
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Pretty accurate zero-crossing detector, just for fun.
On Sat, 25 Feb 2012 00:09:01 +1100, Grant wrote:
On Thu, 23 Feb 2012 15:52:38 -0600, John Fields wrote: Needs a little work, but the concept is that the mains is full-wave rectified and compared with a reference. On the downward slope, when the mains-derived signal crosses the reference, the counters are enabled and a single RESET pulse generated and sent to the up counter, clearing it. It then counts clocks until the mains derived signal goes to zero and starts rising again, and when it crosses the reference this time the counters are disabled and a single pulse generated which broadside loads the Q outputs of the up counter into the D inputs of the down counter, but shifted one bit to the right, (MSB to the left) with the result being that a quantity with a magnitude half that of the up counters contents will be loaded into the down counter. Now, when the mains signal peaks and starts falling again, it will again intercept the reference. When it does, the counters will be enabled, the up counter will be cleared and will start incrementing again, and the down counter will start decrementing until it gets to zero, when a single pulse will be generated. Since the quantity loaded into the down counter was half of the quantity accumulated by the up counter between the two excursions across the reference, then it would take the down counter half that time to time out, and the pulse generated at timeout should be located precisely at the zero crossings of the mains cycles. Well, within 10 microseconds anyway... :-) It takes a few minutes for the sim to run, but I think you'll enjoy it. :-) BTW, copy all the files into a single folder and then click on the .asc file to run it. LTspice should find it and launch it. Three phase? Grant. --- I don't understand. -- JF |
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