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Portable Function Generator and Power Supply

Portable Function Generator and Power Supply. Suketu Kamdar Philip King Ryan Wang Professor Gary Swenson TA: Jon Wheeler. 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

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Portable Function Generator and Power Supply

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  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

  6. 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.

  7. Power Supply (cont’d) • 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

  8. 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

  9. Function Generator (cont’d) • 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

  10. 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

  11. Our Project

  12. Circuit Diagram

  13. 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

  14. Example Waveforms Sine Square Triangle 5 Hz

  15. Example Waveforms (cont’d) Sine Square Triangle 500 KHz

  16. Waveform on Oscilloscope Max Noise: 1 MHz noise, 20 mV in amplitude SNR = 1 V / 20 mV = 50 = 17 dB

  17. 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

  18. 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 don’t provide desired voltage drop • Noise due to wires • Inductance/Capacitance EM noise • Solved using multiple capacitors for filtering

  19. 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

  20. 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

  21. 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

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

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