ELECTRICAL ENGINEERING TECHNOLOGY PROGRAM EET 331 – ELECTRONIC DESIGN LABORATORY EXPERIENCES LABORATORY EXPERIENCE: DIGITAL CONTROL OF AMPLITUDE In recent years we have witnessed an explosion of personal communication and entertainment devices. Cellular phones, MP3 players among others are part of our regular lives. All these device need to be able to adjust the volume of the sound they produce. Years ago, volume control was done using potentiometers that modified the gain of an amplifier. We can see the volume control knobs in some car and household stereos, radios, etc. But if we examine a cell phone, a MP3 player, newer car stereos, we will not find any knobs or potentiometers but pushbuttons. How is then volume control done in these modern devices? How can a pushbutton change the gain of an amplifier? One of the most commonly used solution is to use an integrated circuit that has a resistance digitally controllable instead of the traditional potentiometers that need to be mechanically adjusted. This laboratory exercise will explore the characteristics and possibilities of incrementally controlled digital potentiometers. The goal of this laboratory exercise is to design an amplifier (inverter, non-inverter, differential... you choose) with the following characteristics as shown in the figure below: * Gain of +10 or -10 * 2 control buttons: - Button 1: - Will hold the value of the signal independently of Button 2 or - Will allow the signal to increase or decrease - Button 2: - Will control the direction of the gain (increase or decrease) * Output signal with no DC component * Minimize the number of components used EET 331 – Digital potentimeters 1/3V input V out AMPLIFIER G = 10 CHANGE/ INCREASE/ HOLD DECREASE DIGITAL CONTROL The following are the steps to facilitate the design of the circuit. SECTION 1. ANALYZING THE DIGITAL POTENTIOMETER 1.1 Download the specifications of the Dallas Semiconductor™ DS1804 NV Trimmer Potentiometer (distributed by Maxim semiconductor) and read them. Briefly explain how this device operates. In the laboratory experiment, we will use the DS1804-010 - What is the maximum amount of resistance for this chip? - What is function of each one of the pins? - What is the minimum resistance increment for this chip? SECTION 2. CHARACTERIZING THE DIGITAL POTENTIOMETER ******************************************************************************* IMPORTANT: ALWAYS USE THE TTL OUTPUT OF THE FUNCTION GENERATOR TO DRIVE THE CLOCK SIGNAL FOR THE DS1804 CHIP Use a clock signal between 0.5Hz and 10Hz to observe the effects of the changes of resistance on the signal ******************************************************************************* EET 331 – Digital potentimeters 2/3EET 331 – Digital potentimeters 3/3 2.1 Build a voltage divider circuit in which the Digital Potentiometer is one of the resistors. (Use an AC signal around 1 kHz as the signal to be divided) 2.2 Manipulate the control signals as needed to observe the changes of resistance at both extremes. Using the oscilloscope, estimate the resistance at both extremes. What are those values? What are the values specified by the manufacturer? Are they different? Why? 2.3 Are there any distortion effects? If so, what is the maximum amplitude before distortion becomes noticeable? Why does this happen? 2.4 Evaluate the effect of frequency on the DS1804 chip. Repeat the measurements at different frequencies through all the range provided by the signal generator. Is the DS1804 chip affected by frequency? Can can you be sure that any changes observed are due to the chip and not to the oscilloscope? Devise and explain a method to be sure that the changes are due to the oscilloscope or to the chip. SECTION 3. DIGITAL POTENTIOMETER APPLICATIONS: VARIABLE GAIN AMPLIFIER 3.1 Design, build and characterize the amplifier with the specifications stated at the beginning of this laboratory exercise. 3.2 The majority of the commercial devices will use a pushbutton for increasing and decreasing the volume of the device. The previous system is just a crude approximation. How could you improve the interface to make it more similar to commercial systems? 3.3 Based on your opinion and experience, what are the advantages and disadvantages of using Digitally-controlled potentiometers? SECTION 4. Laboratory report - Create an individual lab report using the guidelines provided in the course’s website. Include all the information that you believe is necessary. - Once again, please comment on the difficulties and challenges of this laboratory work (i.e. what worked, what did not work, what you liked, what you didn’t like, etc.). Be assured that the grade for your laboratory work or your course will not be affected at all by your positive or negative comments. - Comment on the benefits and problems of using these new devices that we have studied in this