Frequency is used to measure the frequency in the range of 4 MHz to 160 MHz and may be used as a radio frequency meter. To be precise, the Exclusive bit pattern works correctly over a wide range of 3,8 MHz to 162 MHz.
- frequency measuring range 4-150 MHz
- readings are displayed through the LCD display
- counter sensitivity 700 mV
- maximum input voltage <30 AT
- very simple circuit, minimum amount of elements, Easy commissioning
- power supply: 8 … 15 In DC.
The scheme shows the frequency nand Figure 1.
The heart of the device is a microcontroller ATTINY2313. Its advantage is the ability to operate at frequencies up to 20 MHz. The model used by the resonator 16 MHz. In this way, microcontroller itself should theoretically correct measure input frequencies up 8 MHz. often, what 8 MHz – This frequency is too low. Increasing the upper frequency measurement may be achieved via frequency divider. The scheme uses frequency divider LB3500, which allows measurements to 150 MHz. LB3500 Degree of separation system is 8. Without using an additional divider circuit must measure the frequency to about 64 MHz. Adding additional divider in the form of binary counter 74LS293 IC1 allows to increase the measurement range of up to about 150 MHz (maximum for LB3500). IC1 divides the frequency of 4. In this way, all the pre-scaler (IC1 and IC4) divides the input frequency on 32. A transistor T1 with C7 elements, R2, R3 acts as a source follower, providing a high input resistance of the system. The input signal after isolation is input LB3500. at the conclusion 9 IC4 you get a signal with 8-fold lower rate, than the inlet. Unfortunately, LB3500 output signal system does not allow for direct control of TTL systems (output has a DC component of about 3 AT, supplied with the variable waveform with amplitude of about 1 AT). The transistor T2 acts as a buffer, circuit IC4 is coordinated with the input circuits IC1. PR1 potentiometer enables precise adjustment. The output signal QB of the counter IC1 is input to the counter T1 IC2. microcontroller program calculates the signal frequency, multiply it by 32, and the measurement result is displayed on the LCD display. PR2 potentiometer allows to adjust the display contrast.
Installation and assembly
The printed circuit board of the frequency of the sample is shown in Figure 2.
Properly assembled scheme should be adjusted potentiometer PR1. Connect the generator (For example, quartz) to the circuit and replace the output 10 chip IC1 (74LS293N) stress about 1,4 B 1.6 B, the system was immediately before the switching state. If the input signal from the oscillator frequency is displayed, the device is ready for operation. The sensitivity of the meter is about 700 mV. Remember, that should not supply more voltage 30 In the input of the meter as this can damage the transistor T1. Frequency meter is powered with stabilized voltage … 8-15AT.