SERIAL
PORT 100KHz FREQUENCY COUNTER
Self powered frequency counter
plugged into the serial port. Included a Visual Basic (VB6) code, PIC code, and a circuit diagram. The PIC16F628A microcontroller is programmed to count the input frequency and transmit
it serially to the serial port. The microcontroller is powered
by the signals of the serial port, so no external power supply is
needed. The counter is 17 bit (16 bits + overflow). The crystal
can be changed to a ceramic resonator if accuracy isn't essential.
The signal input is connected via the chip comparator to allow sensitivity down to 100mV.
You can read more about serial interface in http://www.beyondlogic.org/spp/serial.htm
You are free to use the circuit diagram and the software with no
limitations.
Software includes PIC code and VB6 code. You are free to use the circuit diagram and the software with no
limitations.
The VB6 application
Circuit Description
See also Technical Tips
Pin 4 at the serial port is
turned to +12V by the software enabling RTS. It is regulated to
5V by 78L05. The 5V is the supply to the microcontroller.
Pin 3 is at -12V and pin 7 at +12V
constantly and they are used to drive RX input between -9V (input
HIGH) and +8v (input LOW) . These levels are sufficient to drive
the RS232 input.
PIC16F628A contains a UART for serial comm and a 16
bit counter.
Input signal can be 0.1 to 5 vollts peak to peak.
Pin 17 is the frequency input, it's the PIC comparator input. Referance voltage to the comparator is 2.5V at pin 1. Output of the comparator at pin 2 is linked to the PIC counter input at pin 12.
Pin 8 is the UART output, it transmits the 16 bit count and overflow
in three 8 bit words in RS232 format.
The other pins are not in use but must be left open circuit. |
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