as3935
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| as3935 [2024/04/12 04:26] – river | as3935 [2024/07/25 22:33] (current) – [Calibration] river | ||
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| A badly designed, pulled, aged, uncompensated crystal oscillator might be 50ppm off, so much better than needed as a calibration standard for this application. Therefore can use a µC to calibrate it automatically. I don't see this done in the Sparkfun library even though it seems obvious. | A badly designed, pulled, aged, uncompensated crystal oscillator might be 50ppm off, so much better than needed as a calibration standard for this application. Therefore can use a µC to calibrate it automatically. I don't see this done in the Sparkfun library even though it seems obvious. | ||
| - | The chip can the calibrate its clocks from the above value, so antenna should be trimmed first. | + | The chip can then calibrate its clocks from the above value, so antenna should be trimmed first. |
| Clocks calibration must be repeated after power loss. | Clocks calibration must be repeated after power loss. | ||
| Line 80: | Line 80: | ||
| I wrote a program to test and tune it. Initially found: | I wrote a program to test and tune it. Initially found: | ||
| + | < | ||
| [016412] [D] measure_frequency(): | [016412] [D] measure_frequency(): | ||
| [016412] [D] Trimcap: 0pF, Error: 30214 Hz, 6.0% | [016412] [D] Trimcap: 0pF, Error: 30214 Hz, 6.0% | ||
| Line 112: | Line 113: | ||
| [031442] [D] measure_frequency(): | [031442] [D] measure_frequency(): | ||
| [031442] [D] Trimcap: 120pF, Error: 4244 Hz, 0.8% | [031442] [D] Trimcap: 120pF, Error: 4244 Hz, 0.8% | ||
| - | [031444] [D] Lowest error: 0.848800%. Using 120pF. | + | [031444] [D] Lowest error: 0.848800%. Using 120pF.'' |
| + | </ | ||
| Added 2x 6.8pF NPO caps, soldered on top of and beside the existing caps. Then measured: | Added 2x 6.8pF NPO caps, soldered on top of and beside the existing caps. Then measured: | ||
| + | < | ||
| [020013] [D] measure_frequency(): | [020013] [D] measure_frequency(): | ||
| [020013] [D] Trimcap: 0pF, Error: 9631 Hz, 1.9% | [020013] [D] Trimcap: 0pF, Error: 9631 Hz, 1.9% | ||
| Line 149: | Line 152: | ||
| [035045] [D] Trimcap: 120pF, Error: -13223 Hz, -2.6% | [035045] [D] Trimcap: 120pF, Error: -13223 Hz, -2.6% | ||
| [035047] [D] Lowest error: 0.034200%. Using 48pF. | [035047] [D] Lowest error: 0.034200%. Using 48pF. | ||
| + | </ | ||
| Cleaned off flux and got: | Cleaned off flux and got: | ||
| + | < | ||
| [021200] [D] measure_frequency(): | [021200] [D] measure_frequency(): | ||
| [021200] [D] Trimcap: 0pF, Error: 13863 Hz, 2.8% | [021200] [D] Trimcap: 0pF, Error: 13863 Hz, 2.8% | ||
| Line 185: | Line 190: | ||
| [036237] [D] Trimcap: 120pF, Error: -10133 Hz, -2.0% | [036237] [D] Trimcap: 120pF, Error: -10133 Hz, -2.0% | ||
| [036239] [D] Lowest error: 0.144200%. Using 64pF. | [036239] [D] Lowest error: 0.144200%. Using 64pF. | ||
| + | </ | ||
| I don't know why added the caps seemed to add way more capacitance then expected. It looks like I added more like 80pf rather than the 13.6pF expected. | I don't know why added the caps seemed to add way more capacitance then expected. It looks like I added more like 80pf rather than the 13.6pF expected. | ||
| Line 191: | Line 197: | ||
| Over the next hours I noticed the capacitance drifted back down again, needing more from the trimcaps. Maybe board drying out or cooling down? The next day it was using 96pF or 88pF trimcaps. | Over the next hours I noticed the capacitance drifted back down again, needing more from the trimcaps. Maybe board drying out or cooling down? The next day it was using 96pF or 88pF trimcaps. | ||
| + | |||
| + | Next day, added 51pF. Now it gets: Trimcap: 0pF, Error: -134 Hz, -0.0% | ||
| + | |||
| + | Also added 22uF ceramic to power socket pins, and 1nF from IRQ to ground. Removed electrolytic. Also modified µC board - added bigger 3.3V regulator with ceramic caps and 470uF input cap. | ||
| + | |||
| + | Get occasional QRM reports but nothing like without any caps that started with. | ||
| ===== Noise ===== | ===== Noise ===== | ||
| Line 210: | Line 222: | ||
| (Not extensively tested, maybe reading other registers works too.) | (Not extensively tested, maybe reading other registers works too.) | ||
| - | I read than some boards have wrong tuning caps. I couldn' | + | I read that some boards have wrong tuning caps. I couldn' |
| ===== Links ===== | ===== Links ===== | ||
as3935.1712895993.txt.gz · Last modified: by river