Pocket oscilloscope up to 1 MHz. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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By replacing the PIC1F16A microcontroller with the PIC873F18 [4550, 2] in the pocket oscilloscope described in [3], and the K140UD608 operational amplifier with the TDA8708A analog video interface chip [4], it was possible to reduce the sweep duration by 150 times, to 21 µs for the entire screen width, and increase the maximum frequency of the input signal to 1 MHz. This greatly expanded the capabilities of the oscilloscope.
Main Specifications
- Beam deflection voltage for the entire height of the screen, V ....... 0,2; 1; 3; 10; thirty; 30
- Maximum frequency of the studied signal, MHz ......1
- Horizontal sweep duration, µs ......21, 170, 1000, 10-103, 30-103, 100-103, 300-103, 106
- Screen resolution, px ...... 128x64
- Supply voltage, V ....... 5
- Current consumption, mA.......115
- Dimensions, mm ......80x62x30
- Weight, g.......110
The oscilloscope circuit is shown in fig. 1. The input signal is sent to pin 20 (ADCIN - ADC input) of the DA1 chip (TDA8708A). To start its ADC, the DD1 microcontroller generates clock pulses at pin 17. The binary codes of the signal samples are sent to port B of the microcontroller DD1, which, according to the program, writes them to the RAM, and then displays them on the graphic LCD HG1 in the form of an oscillogram. A general description of the MT-12864J-2FLA LCD can be found in [5], and its use can be found in [6].
Rice. 1. Oscilloscope circuit (click to enlarge)
On fig. 2 shows an oscillogram of a signal with a frequency of 100 kHz. The variable resistor R6 shifts the scan line vertically, setting it to the most convenient position for observing the waveform. A selection of resistor R12 achieves the best image contrast on the LCD screen.
Rice. 2. Oscillogram of a signal with a frequency of 100 kHz
The oscilloscope sweep works in single trigger mode by pressing the SB1 button. By pressing the button SB2, change the duration of the sweep. After each pressing of this button, the value of the new sweep duration is displayed for some time (Fig. 3).
Rice. 3. The value of the new sweep duration
The microcontroller program can be downloaded from ftp://ftp.radio.ru/pub/2015/10/osc4550.zip.
Literature
- Pichugov A. Pocket oscilloscope. - Radio, 2013, No. 10, p. 20, 21.
- PIC18F2455/2550/4455/4550 Data Sheet. - URL: www1.microchip.com/downloads/en/DeviceDoc/39632e.pdf.
- Yatsenkov VS Microchip microcontrollers with USB hardware support. - M.: Radio and communication, 2008.
- TDA8708A. Video analog input interface. - URL: doc.chipfind.ru/pdf/philips/tda 8708a.pdf).
- Liquid crystal module MT-12864J. - URL: melt.com.ru/files/file2150172.5.pdf.
- Milevsky A. Using a graphic LCD MT-12864A with a Microchip microcontroller. - Radio, 2009, No. 6, p. 28-31.
Author: A. Pichugov
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