Portable Function Generator and Power Supply

1
Portable Function Generator and Power Supply

• Suketu Kamdar
• Philip King
• Ryan Wang
• Professor Gary Swenson
• TA Jon Wheeler

2
Motivation

• Build a power supply and function generator for
  use in lab courses such as ECE110 and ECE249
• Allow easier circuit debugging outside of lab
• Create a cheaper solution for student use

3
Objective

• Design a practical tool that provides the
  functionality of multiple components in the lab
• Make it lightweight and portable
• Keep cost down

4
Description

• Power Supply
• 1.5-15V DC, 1A
• Positive/Negative DC Voltages
• Function Generator
• 1Hz-900KHz
• Sine, Square, Triangle Waveforms
• Duty Cycle and DC Offset
• Simple LCD Interface for control

5
Technology

• PIC Microcontroller
• Controls all functionality
• Creates extensive versatility/programmability
• Waveform Generator IC
• Multi-faceted integrated solution
• LCD display-driven interface
• Simple, User-friendly, Optimal

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Power Supply

• Transformer
• Transforms 120V/AC down to ?15V/AC
• Rectification
• Converts AC to DC using diode bridge and
  capacitors
• Voltage Regulation
• Used Voltage Regulator ICs to keep voltages
  constant and steady across loads.

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Power Supply (contd)

• Variable DC Voltages
• 1.5,3,5,9,10,12,15 Volts
• Switched between using PIC microcontroller
• Implemented using a resistor/transistor array
• Output Isolation and Stability
• Diodes used for isolation of outputs
• Capacitors ensure low-noise voltage outputs
• Current-limited output

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Function Generator

• Specifications
• Waveforms Sine, Square, Triangle
• Frequencies 1,2,3,4,5,6,7,8,9 Hz, x10 Hz,
  x100 Hz, kHz, 1MHz
• Duty Cycle Adjust 20-80, stepsize 1
• Waveform Generation IC
• Provides specified waveforms, frequencies, and
  duty cycle
• Controlled by input currents and voltages set by
  digital-to-analog converter (DAC) IC
• Frequency range adjusted using switched capacitor
  array

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Function Generator (contd)

• Digital-to-Analog Converter IC
• Used to control input parameters to waveform
  generator IC
• Controlled by PIC microcontroller
• 8-bit voltage representation between 0 and 2.5
  volts or 5 volts depending on specific use
• reference voltage for waveform generator IC
• Filtering
• Chip Inputs low-passed filtered using capacitors
  to produced cleaner signals

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Control and Display Components

• PIC Microcontroller
• Controls entire unit and functionality
• Routines implemented using assembly code
• LCD Display
• Driven by PIC controller
• Used for menu-driven user-interface
• Simple two button user input
• Toggle and select button system

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Our Project
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Circuit Diagram
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General Functionality Tests

• Compared power supply output to bench supplies in
  the lab using oscilloscope to analyze noise
• Used voltmeter to measure accuracy of output
  voltages
• Similarly compared waveforms to function
  generators in the lab

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Example Waveforms

Sine
Square
Triangle
5 Hz
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Example Waveforms (contd)
Sine
Square
Triangle
500 KHz
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Waveform on Oscilloscope
Max Noise 1 MHz noise, 20 mV in amplitude SNR
1 V / 20 mV 50 17 dB
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Original Design

• Differences
• Used resistors instead of digital potentiometers
  to create variable DC voltages
• Used single PIC Microcontroller chip for manual
  control
• Used switches to select capacitors instead of
  transistors

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Problems and Challenges

• Digital potentiometer
• Allows only a 5 volt drop across the resistor (at
  any pin) 15 volt drop desired
• Surface mount solution too tedious
• Capacitors selected by switches
• Transistors dont provide desired voltage drop
• Noise due to wires
• Inductance/Capacitance EM noise
• Solved using multiple capacitors for filtering

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Successes

• Successfully implemented a power supply and
  function generator
• Improved project design over time while
  overcoming original design problems and
  challenges
• Attained high levels of quality
• Learned a great deal through project
• Cost significantly reduced

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Parts Cost

• Waveform Generator IC 40
• PIC Microcontroller
  4
• LCD Module
  5
• Transformer
  18
• Digital Potentiometer
  12
• DAC, Demux, D-Latches, Relays
  20
• Circuit Components 25
• (transistors, resistors, capacitors,
• voltage regulators, op-amps diodes)
• Miscellaneous 10
• Total Parts Cost 134

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Total Costs

• Labor 96 hours x
  30/hr x 3 people 8640
• Parts Cost 134
• Total Cost 8774

22
Competitive Analysis

• Competitors
• Hewlett Packard/Agilent,Philips, Tektronix
• Strengths
• Affordable, portable, easy to use, software
  upgradeable
• Weaknesses
• Limited but ample functionality

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Improvements

• Apply variable amplitude adjustment
• Allow finer output voltage and frequency
  adjustment
• Offer higher frequencies by using faster op-amps
• Implement adjustable current limiting