PIC Projects
WiFi, Ethernet
Doorbell with SD / EEPROM
SD FAT16/32 for .bmp
TFT Egg Timer
LCD TFT Oscilloscope
SD Talking Clock
SD Sound Recorder,
    FAT32 wav Player
LED Thermometer
LED Egg Timer
LCD Egg Timer

Frequency Counters
100KHz For PC
1MHz For PC
8 Digits LED 50 MHz
Scope Screen Display
LCD Module 10MHz
6MHz for Android
USB PIC18F2550
USB TFT display BMP
USB DS18B20 Sensor
USB Thermometer
USB Counter
USB Meter
USB Oscilloscope
USB Input-Output
USB 16x2 LCD

COM & LPT Ports
MCP3201 on LPT
Serial TFT Text
Serial Inputs Outputs
Serial Port LCD
Analogue Signal to LPT
MCP3201 on Serial Port
Serial Thermometer
Analogue Signal to Serial
LCD Display on LPT
Serial Thermostat

Water Softener
HP Stream 7 docking
3.7V to 5V
Solar Charger

Infrared Decoder
PIC Music

Code Lock
Code Lock with LCD


Self powered frequency counter plugged into the serial port. Included a Visual Basic (VB6) code and .EXE file, PIC assembly, PIC C code, and a circuit diagram. The PIC16F628A microcontroller is programmed to count the input frequency and transmit it serially to the serial port. The micro controller is powered by the signals of the serial port, so no external power supply is needed. The counter is 20 bit transmitted by the UART in 3 bytes. The crystal can be changed to a ceramic resonator if accuracy isn't essential.

You can read more about serial interface in

Code is for MPLAB, MPLABX and compilers HI TECH or XC8.

The VB 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 RS242 input.

Pin 12 is the frequency input, input signal has to be TTL type.
Pin 8 is the UART output, it transmits the 20 bit count in three bytes in RS232 format. When pin 8 is high both transistors conduct and voltage at pin 2 of serial port is at -9V.
The other pins are not in use but must be left open circuit.


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