Digital oscilloscope and Function generator

. INTRODUCTION

So many of the experiments in the advanced labs make use of oscilloscopes and function generators that it is useful to learn their general operation. Function generators are signal sources which provide a specifiable voltage applied over a specifiable time, such as a “sine wave” or “triangle wave” signal. These signals are used to control other apparatus to, for example, vary a magnetic field (superconductivity and NMR experiments) send a radioactive source back and forth (Mossbauer effect experiment), or act as a timing signal, i.e., “clock” (phase-sensitive detection experiment). Oscilloscopes are a type of signal analyzer—they show the experimenter a picture of the signal, usually in the form of a voltage versus time graph. The user can then study this picture to learn the amplitude, frequency, and overall shape of the signal which may depend on the physics being explored in the experiment. Both function generators and oscilloscopes are highly sophisticated and technologically mature devices. The oldest forms of them date back to the beginnings of electronic engineering, and their modern descendants are often digitally based, multifunction devices costing thousands of dollars. This collection of exercises is intended to get you started on some of the basics of operating ’scopes and generators, but it takes a good deal of experience to learn how to operate them well and take full advantage of their capabilities.

1.2 Objectives

The goal of this project is to design an oscilloscope and function generator. The designed instrument is a low cost, highly effective and portable device. Here are some of the objectives of our project:-
• To view different waves on the monitor.
• Easy to handle
• Portable during handling
• Accurate detection of signals
• Real time hand held implementation

1.3. Scope and application

Oscilloscope is commonly used in the lab to view different signals. Some of the scopes of this project are as follows:-
• In medical field
• Engineering labs
• Research centers
1.4 Statement of problems

Digital oscilloscope, nowadays available in market is very costly that it is un-affordable to every persons. Affordable can be made only by the institution for students. But this is hand held oscilloscope and can be affordable by everyone. It works as both oscilloscope and function generator. While the Digital Oscilloscopes and Function Generators in lab are functionally useful, nowadays digital oscilloscope do not make for portable or cost-effective products. Digital Oscilloscope and Function Generator provides a simple, easy to use alternative that provides the functionality from both these devices for less amount. Digital Oscilloscope and Function Generator can used in lab and anywhere.

1. LITERATURE REVIEW

A digital oscilloscope is a complex electronic device composed of various software and electronic hardware modules that work together to capture, process, display and store data that represents the signals of interest of an operator. Digital oscilloscopes are often referred to as digital storage oscilloscope (DSO) or digital sampling oscilloscopes (DSO).
In its simplest form, a digital oscilloscope features six elements — the analog vertical input amplifiers, analog-to-digital converter and a digital waveform memory, a time base which features a triggering and clock drive, the circuits for waveform display and reconstruction, the LED or LCD display, and the power supply. Digital oscilloscopes periodically samples a time varying analog signal and stores in the waveform memory the signal’s values in correlation with time. Using an internal clock, digital oscilloscopes chops input signals into separate time points. The instantaneous amplitude values are then quantized by the oscilloscope at those points. The resulting digital representations are then stored in a digital memory.
At a predetermined clock rate, the display is regenerated from the device’s memory and is consequently viewed as connected dots or a series of dots. Digital Oscilloscopes provides powerful features on how they trigger the digitized data from its memory. Some of the advantages of a digital oscilloscope over analog often referred to as digital storage oscilloscope (DSO) or digital sampling oscilloscopes (DSO).
In its simplest form, a digital oscilloscope features six elements — the analog vertical input amplifiers, analog-to-digital converter and a digital waveform memory, a time base which features a triggering and clock drive, the circuits for waveform display and reconstruction, the LED or LCD display, and the power supply. Digital oscilloscopes periodically samples a time varying analog signal and stores in the waveform memory the signal’s values in correlation with time. Using an internal clock, digital oscilloscopes chops input signals into separate time points. The instantaneous amplitude values are then quantized by the oscilloscope at those points. The resulting digital representations are then stored in a digital memory.
At a predetermined clock rate, the display is regenerated from the device’s memory and is consequently viewed as connected dots or a series of dots. Digital Oscilloscopes provides powerful features on how they trigger the digitized data from its memory. Some of the advantages of a digital oscilloscope over analog oscilloscope include the scope’s ability to store digital data for later viewing, upload to a computer, and generate a hard copy or store on a diskette and its capacity to instantly make measurements on the digital data. After a trigger event, digital oscilloscopes can be made to display the waveforms as compared to an analog oscilloscope that needs to be triggered first before it starts a trace. A digital oscilloscope also has the ability to examine digitized information stored in its memory and make automatic measurements based on the selected parameters of the user, such as voltage excursion, frequency and rise times. It can also display similar captured data in various ways. This capability is attributed to the presence of more captured data than what shown on the screen. It also offers the flexibility of providing a vast array of storage, processing and display options, such as graphics and one-quarter and one-half screen displays and multiple step processing programs.
A digital oscilloscope is ideal for displaying intricate signal waveforms where calculations and measurements on specific portions of the waveforms must be made to provide numerical and waveform output displays which reflects the chosen parameters of the waveforms. The two general categories of digital oscilloscopes are single shot oscilloscopes and random interleave or equivalent time sampling oscilloscopes.
Single shot oscilloscope starts real-time sampling of an event after a trigger condition has been satisfied. The speed of the analog-to-digital converter determines the limitations of the sampling speed of single shot oscilloscopes. The size of the device’s acquisition memory, which receives the output from the converter, limits the time on which a single event can be sampled. Meanwhile, random interleave oscilloscope or equivalent time sampling oscilloscope relies on sampling repetitive events at different points over certain periods of time. The hand held oscilloscope is simple to take care and it is portable to carry from place to place. The price for this machine can be affordable for every individuals.

1. METHODOLOGY
   3.1 BLOCK DIAGRAM
   
   Fig3.1: Block diagram of Oscilloscope and Function Generator

3.2 Block diagram description

Fig (3.1) shows block diagram of oscilloscope and function generator consists of two block raspberry pi (HDMI output, USB input, SPI master) and PIC 32 (SPI slave, ADC, SPI master).
USB input connected to mouse and keyboard to get input and HDMI output connected to monitor. SPI master of Raspberry pi is bi-directional connected to SPI slave of section PIC 32. SPI master joined to digital to analog connector generator voltage waveforms joined to ADC and input voltage is connected here. Raspberry pi free to monitor waveform and produce digital display and interface. To perform the plotting voltage signal in input of ADC. The PIC 32 read voltage then send voltage information after converted in digital raspberry pi over SPI connection.

1. HARDWARE COMPONENTS

4.1 Raspberry pi

The Raspberry Pi is a series of small single-board computers developed in the United Kingdom by the Raspberry Pi foundation to promote the teaching of basic computer science in schools and in developing countries. The original model became far more popular than anticipated. Raspberry Pi is an open-source development environment and programming language. While it's very flexible and powerful, it's mainly used in the realm of visual arts.
Fig4.1: Raspberry pi

4.2 DAC and ADC

In electronics, a digital-to-analog converter (DAC) is a device that converts a digital signal into analog signal and analog-to digital converter is a device that performs analog signal to digital signal. There are several DAC architectures, the suitability of a DAC for a particular application is determined by three main parameters: resolution, maximum sampling frequency and accuracy. Due to the complexity and the need for precisely matched components, all but the most specialized DACs are implemented as integrated circuits. DACs can degrade a signal, so a DAC should be specified that has insignificant errors in terms of the application. DACs are commonly used in music players to convert digital data streams into analog audio signals. They are also used in televisions and mobile phones to convert digital video into analog video signals which connect to the screen drivers to display monochrome of color images. These two applications use DACs at opposite ends of the speed/resolution trade-off. The audio DAC is a low speed high resolution type while the video DAC is a high speed low to medium resolution type.

4.3 PIC-32 Microcontroller

PIC is a family of microcontrollers made by Microchip Technology. Derives from the PIC1650 originally developed by General Instrument’s Microelectronics Division. PIC stands for Peripheral Interface Controller. The first parts of the family were available in 1976. Early models of PIC had read only memory (ROM) of field programmable EPROM for program storage, some with provision for erasing memory. All current models use flash memory for program storage and newer models allow the PIC to reprogram itself. Some of the specifications are:-
• Floating Point Unit for fast single- and double-precision math
• 16 KB to 2 MB Flash
• Fast interrupts and context switch

4.4 Potentiometer

A potentiometer is used to test the design initially when the function generator was not working. This was set so that we could sweep the voltage between 3.3 and 0 V. It was connected to the analog to digital converter in the PIC32. This served as a quick way to verify the oscilloscope functionality of our device.

4.5. Monitor

Monitor is an instrument or device used for observing, checking or keeping a continuous record of a process or quality. Originally, computer monitors were used for data processing while television receivers were used for entertainment. From the 1980s onwards, computers (and their monitors) have been used for both data processing and entertainment, while televisions have implemented some computer functionality. The use of monitor in this project is to display the wave shapes transmitted by raspberry pi.

1. Tools and technique

5.1 Raspberry-pi

Python is a wonderful and powerful programing language that’s easy to use (easy to read and write) and with Raspberry Pi 3 lets our project to the real world. Raspberry pi 3 being very cost productive can be located in large numbers in underdeveloped and developing countries, to schools and colleges and to everyone who is interested in computer and electronics. It can be used to handle small servers. It can be also used in engineering robotics for efficient results and in medicinal fields also. We are using in this project for plotting the waveform.

5.2 SPI communication

SPI stands for Serial Peripheral Interface. Here in this project we are going to use the spider library to run SPI communication on the raspberry pi. It would first set the chip select low to indicate the start of a transaction, send the data was given as the argument of the function and then read data from the SPI. It then set the chip select high to end the transaction and returned the voltage that it received via SPI .

1. Expected output

SPI (Serial Port Interface) is used bi-directional in nature one master and slave nature. Voltage waveform from DAC is joined to ADC along with potentiometer. Finally, combined function of oscilloscope and function generator is display waveform accurate.

References

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[5]. "C2G | Shop For A/V, PC, Rapidrun And Networking Cables And Devices". Cablestogo.com. N.p., 2017. Web. 17 Mar. 2017.