Frequency Meter and Pulse Generator with RS232 Interface

An Atmel AT90S2313 microcontroller is used to build this RS232 frequency meter which can communicate at 9600 baud through an RS232 terminal program which eliminates the use of any front panel controls.

The internal UART of AT90S2323 is the serial interface that is connected to the outside world through RS232 where a MAXIM MAX232 chip is used. The RS232 drive voltages are derived from the 5V supply. A 7805 5V voltage regulator is used to supply the power input. Connected between the 5V supply and ground is a pair of LEDs along with current limiting resistors in series. The current through one LED or the other is shunted by one pin on the AT90S2313. The chip flips between the combined counter and frequency meter.

The device is ready when one LED is ON which does not measure input frequency and does not generate pulses on the output. The device is actively measuring frequency or generating pulses when the other LED is ON. This causes one of the LEDs to be ON at a time wherein quick visual confirmation that power is applied and the state of the device are allowed.

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