Microwatt Meter with 50 MHz Frequency

Overview

The project was designed to create a simple microwatt meter that has an input range of -75dBm to +5dBm and a frequency range from 2 to 50MHz.

Explanation

The meter utilizes a PIC16C84 as controller, an AD606 as log converter, a MAX186 as ADC, and a HD44780 type LCD. The level and frequency of the input signal is being measured by the PIC and then calculating the level in dBm using frequency-dependent factors. The PIC16C84 microcontroller has simple architecture, cheap, 1024 words of EEPROM program memory, and easy to program. The LCD character displays is made possible using a Hitachi HD44780 controller. A simple C program was used to test the LCD displays connected to a PC parallel port.

The device is using the AD606 while the PIC controls an ADC to measure the AD606 output voltage and also count the AD606 limiter pulses to give an indication of the signal frequency. The frequency is measured by counting pulses during one millisecond which is determined by a delay loop. The counter is activated during this time by three-stating another pin connected to the counter pin. Pulling this pin low will stop the counter.