jazz 209 Posted February 3, 2013 Share Posted February 3, 2013 I made simple frequency meter with basic MSP430F550x board without any other parts. Only 24MHz XT2 is used. XT1 is not used, but it can stay on board, no problem. Firmware size is 1.5 kB, and it is starting from $E000, so it will work with any MSP430F550x familly member. Measuring pin is TA1CLK, sequence takes 1 second, and resolution is 1 Hz. Don't have some precize clock source for calibration, so I used for checking PCM2707 3.3V USB to I2S audio bridge that I have on hand. By default word select frequency is 48 kHz, and clock is 64 * 48 kHz = 3.072 MHz. For calibration use presize MHz clock. First byte in firmware file (default $7D), at location $E000 is used for calibration. If mesuring result is lower than real value, increase calibration byte value, and opposite. The Best way is to change calibration byte value by one (not +/- 10) with each step. When board is pluged to USB port it will be enumerated as CDC (virtual serial port), and measured results will be displayed by any terminal tool (Hyper Terminal for Win32). Measuring results with measuring pin connected to ground:  0 Hz  0 Hz  0 Hz Measuring results with measuring pin connected to 48 kHz:  48000 Hz  48000 Hz  47999 Hz  48000 Hz  48000 Hz Measuring results with measuring pin connected to 3.072 MHz:  3071997 Hz  3071998 Hz  3071998 Hz  3071997 Hz  3071995 Hz  3071995 Hz  3071995 Hz  3071995 Hz  3071995 Hz  3071995 Hz  3071995 Hz  3071995 Hz  3071997 Hz  3071996 Hz Firmware: fm.zip RobG, jsolarski and larsie 3 Quote Link to post Share on other sites
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