digi mul ppt

Project on
DIGITAL MULTIMETER DESIGN
(USING VHDL)
Presented by:
o Mohit Mukul 1104030
o Harsh Prakash Singh 1104062
o Rahul Kumar 1104063
Under the supervision of : Mr. Bibhuti Bikramaditya
(TekBrains Pvt.ltd.) and
Dr. Bijay Kumar Sharma
Deptt. Of ECE, NITP
DEPARTMENT OF ELECTRONICS & COMMUNICATION
ENGINEERING,
NIT PATNA

 Introduction
 Objectives
 Platforms used
 Mechanism
 Working parts
 Work done
 Conclusion
 Future scope
 References
Phases of the project

1.1 Digital Multimeter(DMM)
 An electronic measuring instrument that combines several measurement
functions in one unit, viz. voltage, current, resistance, beta of the
transistors, etc.
 Display the measured value in numerals
 More common than the analog multimeters.
 The signal under test is converted into voltage and an amplifier with
electronically controlled gain preconditions the signal.
Introduction

1.2 VHDL
 VHDL stands for VHSIC (Very High Speed Integrated Circuits) Hardware Description
Language
 A hardware description language which describes the behaviour of the circuit based
on the logic implemented
 Intended for circuit synthesis and circuit simulation
 A standard, technology/vendor independent language and so is portable and
reusable.
 Applications in the field of Programmable logic devices(PLD’s)
-- Complex Programmable Logic Devices (CPLD’s)
-- Field Programmable Gate Arrays (FPGA’s)
and in the field of Application Specific Integrated Circuits (ASIC’s)
 Statements are concurrent i.e., executed parallely. So VHDL is sometimes also called
code.
 In VHDL, statements inside a PROCESS, FUNCTION and PROCEDURES are processed
serially.
Contd.

Summary of VHDL design flow:
Contd.

1.3 FPGA
 FPGA stands for Field Programmable Gate Array
is an IC designed to be configured by a designer
after manufacturing. So, Field Programmable.
 Configured using a HDL
 An array of programmable logic blocks
which can be reconfigured
 Perform complex combinational functions or
simple logic gates and even include simple
flip-flops
Contd.

 To design, build and test a multimeter comparable in performance to
some extent with the multimeters available at the ECE laboratories.
 Use a FPGA kit to implement the logic component of our circuit
(programmed via VHDL) and also for its LED and LCD displays to
showcase the functionalities of our multimeter.
 The basic design of the VHDL code is a system to :
-- Control the flow of the following states- Reset/Display, Count-
Up, Set-Sign, Countdown and Binary-BCD Decoding
-- Manipulate the four registers to fluctuate between the
ohmmeter, voltmeter, ammeter and the Beta calculations.
-- Use the LCD drivers to signal the current state.
Objective

 Xilinx Vivado 2014.1
 ModelSim SE 6.2g (Mentor Graphics)
 Xilinx SDK 2014.1
 Windows 7
Platforms used

Modes of DMM:
1. Voltmeter 2. Ammeter
3. Ohmmeter 4. Beta calculator
 Built by chip soldering on the Electric Circuit Board (ECB)
 Run by FPGA kit, which is controlled by the VHDL code
 FPGA sends the signals to the ECB contained in a black box
Main parts of the DMM:
1. VHDL code 2. Power Supply
3. Voltmeter circuit 4. Ammeter circuit
5. Ohmmeter circuit 6. Beta calculator circuit
7. Metal enclosure
Mechanism

 The FPGA is sync. with the fundamental Voltmeter circuit to perform as
per the VHDL code
 Voltmeter circuit is the basic circuit and serves as a platform
 Ohmmeter uses the voltmeter to know the unknown R by passing a
small constant current
 Ammeter uses the voltmeter and a difference and inverting amplifier to
find the current
 Power supply steps down the AC voltage and converts it into DC.
Contd.

 VHDL code
 Power supply
 Voltmeter
 Ammeter
 Ohmmeter
 Beta calculator
 Metal enclosure
Working parts

-- serves as the brain of the DMM
-- works as counters, registers, decoders, multiplexers, range
checkers, drivers and state machines
Modules of the VHDL code:
-- up and down counters
-- range check modules (not a part of the State machine)
-- binary to BCD converter
-- LCD driver
-- 4 bit register to store the current mode
VHDL code

States of the state machine:
1. reset/display 2. count up 3. set sign 4. count down 5. binary-bcd decoding
Reset mode:
1. Resets all registers to store new BCD value for display
2. Resets the integrator by shortening the capacitor
Count up mode:
1. Up counter measures a particular time(say 500ms) while Vin is enabled and passed
to integrator
2. After time, counter signals to pass to next state
Set sign mode:
1. Output from the voltmeter comparator is inverted and saved in a latch
2. If Vcomparator>Vg, Vin is –ve or vice versa
3. Output of latch is passed to mux to decide the Vref (+5/-5 volts)
State machine

Count down mode:
1. Stays in this mode until Vcomparator changes from high to low or vice
versa
2. Down counter is enabled to store time in binary
Binary to BCD converter mode:
1. Time in binary is converter to BCD
2. Binary is used for easier computation
 Working of State machine is based on the Moore’s style state principle
Contd.

Voltmeter circuit consists of:
1. Integrating op-amp
2. Comparator
3. Multiplexer
4. Relay switches
 Integrator and Comparator form the main part of the ADC
 Multiplexer provides the Vref as per the sign of Vin
 Relay switches are used to choose between Vin and Vref and to reset
the integrator
 Circuit communicates with the FPGA to work as a full voltmeter
Voltmeter

Ammeter circuit consists of the following chips:
1. Difference amplifier
2. Inverting amplifier
3. Multiplexer
4. Resistors of diff. values
 Difference amplifier amplifies [Vth-Vin] and is then inverted
 When Vth is 0, ouptut from inverting amplifier is +ve
 Multiplexer switches between diff. channels to get the output voltage
in the desired range
Ammeter

 Different constant current sources for different range of the resistances
 4 to 1 multiplexer to choose a range
Schematic diagram of Ohmmeter circuit:
Here, Re is calculated by the formula:
 (5-0.7)/Re=0.00001 as Vref=5V and
Vbe=0.7 V and constant current=0.01mA
 Measuring the drop across the passive
element and multiplying by 10000, we get the load resistance.
Ohmmeter

 Constant base current is sent using a constant current source
 Ib=0.1mA for both types npn and pnp transistors
 Variable resistor is used to make accurate value of resistor
 Transistor acts as current amplifier Ic= β x Ib
 Voltage across the collector resistance is measured to get the Ic
Beta (β) Calculator

Circuit diagram for β calculator

Written VHDL codes for the following registers and simulated and
synthesized them on Xilinx.
--Flip-flops --Binary-BCD converter
--Latches -- Ranger checker modules
--Comparators -- LCD driver
--Encoders -- State machines
--Decoders
--Multiplexers
--Demultiplexers
--Counters
Work done

 Complete replacement of analog multimeters due to:
-- higher accuracy
-- higher durability
-- no parallax error
 Modern DMM’s have a no of measurement enhancements which include:
-- Auto ranging
-- Auto polarity
-- Sample and hold
--Graphical representation of the quantity under test
-- A low bandwidth oscilloscope
-- Simple data acquisition features
Future Scope

 We use VHDL to run the FPGA kit to control the different modes of
DMM
 Channel to these circuits is switched when button on the board is
pressed
 Power supply provides the various voltages to the chips in the circuits
 Combining these circuits together and putting them in a black box, we
build our DMM using VHDL.
Conclusion

 "Slope (integrating) ADC." : DIGITAL-ANALOG CONVERSION. N.p., n.d. Fri.
20 Oct. 2012. <http://www.allaboutcircuits.com/vol_4/chpt_13/8.html>.
 www.TekBrains.org (Bibhuti Vikramaditya)
 "Www.datasheetcatalog.com." Www.datasheetcatalog.com. 21 Oct. 2012
<http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1981.pdf >.
 "How Analog-to-Digital Converter (ADC) Works | Hardware Secrets." How
Analog-to-Digital Converter (ADC) Works | Hardware Secrets. N.p., n.d. Sat.
21 Oct. 2012. <http://www.hardwaresecrets.com/article/How-Analog-to-
Digital-Converter-ADC-Works/317/8>.
 ”Current Source”. Current source From Wikipedia, the free encyclopaedia
N.p. 14 Nov 2012. Retrieved 20 Nov.2012<
http://en.wikipedia.org/wiki/Current_source>
 www.wikipedia.org
References

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