ECE 110/120 Honors Lab Section : Digital Multimeter

Introduction

Statement of Purpose

• The overall aim of this project is to build a digital multimeter using analog to digital converters, a decoder and a seven segment digital display. Our initial goal is simply to have a working digital voltmeter that can measure DC voltages with a degree of accuracy around 10 mV, but if that ends up taking less time than expected, we want to add further functionality in the form of an ammeter and potentially an ohmmeter

Background Research

• As of right now, the vast majority of the research that we have done is related to constructing a digital voltmeter because this is our initial goal (the ammeter and ohmmeter are still under consideration). We have looked into several other projects focused on making a digital voltmeter, but many of them were either using some sort of microcontroller and/or integrated ADC chip to convert the analog signal and display it. With our project, we want to approach the idea of a digital voltmeter from a slightly lower level and will be constructing our digital ramp ADC from smaller components. The ADC will then give us the binary output that we need to read the voltage using traditional display hardware (decoder, 7-segment display, etc).

Design Details

Block Diagram / Flow Chart (Voltmeter Only)

System Overview

The first step in measuring the voltage across a given element is inputting the analog signal into the ADC that we will construct. The ADC will then convert the analog signal to a digital one that can be interpreted by the decoder. Next, the digital signal, a binary representation of the analog signal, is input into the decoder. The decoder takes the binary signal and turns it into a value for each LED element of the 7-segment display. This allows the display to actually interpret the output of the ADC and thus show correct values.

Parts List (tentative)

1. Counter
2. Discrete DAC
3. SRG
4. PWM Generator for the Clock Pulse (possibly a relaxation oscillator)
5. Comparator Op-Amp

6. Binary decoder

7. Three 7-segment digital displays (one with a decimal point)

Possible Challenges

• One of the challenges that we can already see from the very beginning is the issue of accuracy in the readings that our multimeter will be making. Due to the fact that we are building the ADC ourselves for this project (i.e. no microcontroller), our ability to capture voltages precisely on a very small scale might be limited by the relative crudeness of our design (e.g. the lower resolution that we might get out of the ADC we are making).

References

• [0] Allaboutcircuits.com. (2018). Introduction to Digital-Analog Conversion | Digital-Analog Conversion | Electronics Textbook. [online] Available at: https://www.allaboutcircuits.com/textbook/digital/chpt-13/digital-analog-conversion/  [Accessed 16 Feb. 2018].
• [1] "Simple Digital Voltmeter Circuit Diagram using ICL7107", Circuitdigest.com, 2018. [Online]. Available: https://circuitdigest.com/electronic-circuits/simple-digital-voltmeter-circuit-diagram [Accessed: 16- Feb- 2018].

Atharva Sehgal (atharva2) (ECE120)

Can Gulseren (cang4) (ECE120)

Benjamin Cross (bc8) (ECE 120)