Electronics Fabrication and Assembly Workshop

School of Mechanical Engineering

Objectives

Objectives: Transmitting Information▪ Understanding of Signals and Signal types▪ Noise and Signal to Noise Ratios

Understanding Electronics Hardware▪ Review of Basic Components▪ Understanding Transistors – Bipolar and MOSFET▪ Understanding of modules and modular design▪ Basics of Microcontrollers▪ Arduino + Compact Rio

▪ Understanding of Electronics Sensors▪ Understanding of Motor types and Motor Controllers▪ Understanding of types of wire and wire routing▪ Understanding Fuses and Emergency Stops

Objectives continued

More Objectives: Schematics and Wiring Diagrams Instrumentations, Assembly and Troubleshooting▪ Basics of troubleshooting▪ Type of Instrumentation▪ DMM▪ Oscilloscope

▪ Types of Circuit Boards▪ Type of Component packages▪ Basics of Soldering▪ Cold Solder Joints

Build and test a circuit (project) To Have Fun!

Transmitting InformationSignal types and Noise

Types of Signals

Types of Signals: Analog Voltage (0-10V)▪ Sine Wave

Digital (I/O, TTL)▪ Binary – either ‘ON’ or ‘OFF’▪ TTL – Transistor to Transistor logic – 5V HI, 0V LOW

Analog Current (4-20mA)▪ Analog – think of Voltage across a resistor via Ohms law: V=I*R▪ Commonly used in Industrial Controls

PWM (Pulse Width Modulated) signal▪ Square wave, variable duty cycle

Serial, Ethernet, GPIB, CAN▪ Negotiated Protocols for sending data

Analog Signal – 0-10V

Digital Signal - TTL

Current Signal – 4mA – 20mA

PWM Signal

Noise and Signal to Noise Ratio

Noise is electrical potential energy that is injected into wires in your circuits.

Noise can be generated by numerous sources, some internal to your project and some external▪ Motors and/or motor drives ▪ Poor wiring practice (crosstalk)▪ Fluorescent lighting▪ Ripple from the incomplete conversion of AC power to DC power in

power supplies▪ Electrochemical reactions (in batteries)▪ Ground loops due to ‘floating’ or high resistance ground connections

The Signal to Noise Ratio is simply the magnitude of your desired signal in relation to the magnitude of the ambient noise. The higher the SNR ratio, the better the noise rejection and purer the desired signal will be.

Noise and Signal to Noise Ratio

Noise is something you should consider and account for in your electrical projects. You can reduce noise by several means including:▪ Good wiring techniques and wire routing▪ Using ‘bypass’ capacitors on DC power supplies▪ Using metal shields and shielded wire▪ Using wire such as twisted pair and/or Coaxial cable▪ Using good grounding techniques▪ Use amplifiers to increase the magnitude of signals

Not all noise is important. Understand your signals and what they mean for your project to determine whether ambient noise is something you need to work with.

Noise and Signal to Noise RatioSignal and Noise with similar Vpp and average DC level

Noise and Signal to Noise RatioSignal and Noise with similar Vpp and average DC level

Notice how when the desired signal’s magnitude is very similar to the magnitude of the ambient noise, the resultant signal is very different than that of the desired signal.

Noise and Signal to Noise RatioSignal and Noise with similar Vpp but different average DC level

Noise and Signal to Noise RatioSignal and Noise with similar Vpp but different average DC level

Notice that even if we shift the desired signal up in voltage, if the magnitude of the signalremains similar to the magnitude of the ambient noise, our total signal is not representative of the desired signal

Noise and Signal to Noise RatioSignal and Noise with different Vpp and different average DC level

Noise and Signal to Noise RatioSignal and Noise with different Vpp and different average DC level

Notice how the resultant signal with noise is not significantly different than the original ‘clean’ signal

Demo – Crosstalk and Noise

Demo: Noise injected from a single wire to parallel wires of different types over a length of 6 feet.

Type of HardwareElectronics Components and Modules

Basic Electronic Components

Resistors, capacitors, inductors used to control current, change frequencies, build passive filters etc

Integrated circuit chips (IC’s) Can be analog or digital in nature and allow you to complete

advanced tasks in a singular package▪ Op-Amps▪ Timer▪ Microcontrollers

Diodes Used to control direction of current flow. Can be used to convert AC

into DC. Also used in protection circuits for motors and power supplies

Transistors Building blocks for most integrated circuits and microcontrollers Can be a Bipolar or a MOSFET type Used in current amplifiers or electronic switches

Transistors, bipolar

Known as NPN or PNP based on materials used in construction. Also called small signal transistors.

Three terminals, Base, Collector and Emitter

Fundamentally bipolar transistors are a current amplifier and each has a gain known as hfe.. This is a ratio of current supplied to the Base terminal and the current available at the Emitter terminal. Gains of 100-1000 are common.

Although these are current amplifiers, they can be used as electronic switches

Can be used to interface a microcontroller output to control a 12 volt relay. (image)

Base

Collector

Emitter

Transistor driver for a 12 volt relay coil

Input

Transistors, MOSFET

MOSFET may also be called power transistors due to the capability to handle large currents.

MOSFET is Metal Oxide Semiconductor, Field Effect Transistor

Three terminals, Gate, Drain and Source Fundamentally, MOSFET’s are a switch.

When the proper charge is applied to the Gate, current can flow from the drain to the source. In practical terms, zero current is required at the Gate to operate the transistor.

Commonly found in ‘H bridge’ motor drives and other high power amplifiers.

Can be used to interface a small switch to turn on or off a larger motor. (image)

Transistor switch to turnon/off a motor

Basics of Electronic ‘Modules’

A module is a collection of discrete electronic components assembled in a way to serve a specific function. These offer pre-engineered solutions for specific common applications and have well defined input signals and output signals.

Modules come in numerous shapes/size and functions. Motor drive Digital Compass Ultrasonic Range Finder Microcontroller kit (Arduino)

Some Key Aspects: Supply Voltage Required Supply Current Required Output Drive Capacity (current drive) Output Signal type Input Signal type Input current required Connectors used

Microcontrollers - Software

A microcontroller is a great option to use for complicated functionality. Microcontrollers can have many means of communications, several inputs and outputs of different types and a high level language to configure the device.

A key consideration for your design and software is understanding the states of the outputs for your microcontroller and the results with your machine Power up – what state are outputs in? Is that condition

defined? Software crash – what happens to your outputs? Race condition/hung software – what happens? Timing – how long for input/output to stabilize to be valid?

Microcontrollers - Arduino

The Arduino microcontroller is a low cost, versatile option for many senior design projects

There are numerous models ranging from the Arduino Micro to the Mega. Different models will have differing numbers of

Inputs/Outputs (PWM), clock speed, RAM etc Arduinos use a C syntax codebase with an open

source Integrated development environment Numerous add-ons in a ‘shield’ format to plug

directory into the development board. We have some Arduinos and Intel Galileos

available in ME 2042.

Microcontrollers – Compact Rio

The Compact Rio (and MyRIO) microcontroller is a moderate cost microcontroller from National Instruments and uses the LabVIEW programming Environment.

There are numerous models ranging 8 slot cDAQ chassis to the single board RIO or MyRIO. Different models will have differing numbers of

Inputs/Outputs (PWM), clock speed, expansion capability The Compact RIO cDAQ platform takes modules that allow

a mix and match set of capabilities. Modules include AI, AO, DIO, Thermocouple, Bridge amplifiers, Motor Drives etc

We have four Compact Rio Chassis available in ME 2042.

Sensors

Example Types: Light Proportional position (IR, ultrasonic, laser) Digital position (IR, ultrasonic, Laser) Flex Accelerometers Magnetic (reed switch, hall effect) Acoustic (microphone, piezo) Linear position (linear potentiometer, LVDT) Switch (digital on/off) Strain Gauges Rotary position (encoders, potentiometers)

Key Aspects: What is voltage and current required to operate sensor What is the signal type of its output Is there a signal conditioner/amplifier required

Motors and Motor Drives

Types: Stepper Induction Servo Solenoid Brushed/Brushless Linear

Controllers: Stepper Drive (1/2 step, full step) H Bridge Frequency Drive PWM speed control

Microcontrollers CANNOT directly power motors – a Motor Drive is required!

Stepper Motors

The stepper motor ‘steps’ from angle to angle when asked Requires a stepper

motor drive▪ Usually requires 3 DIO

controls, Enable, Step and Direction.

Motors come in bipolar or 3 phase configurations▪ Motor is rated in steps

per revolution. Using ‘half step’ mode can double resolution.

AC Motors – Servo Motor

The AC motor is a simple motor that will rotate when powered. Adding feedback causes it to become a servo motor.

AC Motors come in single phase and 3 phase variants. In general, you cannot do speed control on a single phase motor.

AC three phase motors can use a Frequency Drive to control speed.

External controller coupled to a feedback mechanism can give exact position control

DC Motors – Servo Motors

The DC motor is a simple motor that will rotate when powered. Changing the polarity of the power cables will allow you to reverse direction.

Adding feedback causes it to become a servo motor.

Requires a motor drive for speed control DC Motors use PWM drives

External controller and some type of positional feedback can allow for position control

Brushed DC Motor

RC Servo Motor

The RC Servo is an assembly of a motor, potentiometer, gearbox and PCB controller to translate a PWM signal into a position.

These require power and RC PWM signal to operate. The PWM signal has a period of

20ms. The pulse width will determines position▪ 0.5ms pulse width is minimum, 1.5ms

pulse width is neutral and 2.5ms is maximum.

▪ Above translates to full left, middle and full right for RC servo shown

The RC servo is nothing more than a DC motor with feedback controls integrated into the device

Common Interface Devices/Modules

Transistor Current Amplifier Module Used to take a low current drive output from

Microcontroller and turn on a solenoid or relay coil

Relay/Solid State Relay Electrically controlled switch. Relays are

mechanical, Solid State Relays are all electronic components

Transistor Switch Solid State implementation of a relay

Mechanical Switch – for microcontroller input Method for a microcontroller to understand

the state of a mechanical switch (image)

Circuit to interfaceswitch to microcontroller

Debouncing Mechanical Switches

A mechanical switch used as an input is not a true impulse function. It will oscillate from high to low before stabilizing Use a switch debouncer to

correct this issue

Demo – Switch Debouncing

Demo – Impulse Count for a single closure of a mechanical switch

Wire and Wire Types

Sized by gauge - AWG Smaller gauge number = bigger wire Current capacity determined by gauge of wire

and temperature rise of wire. In general, thicker wire will be smaller gauge number and can carry more current.

Solid/Stranded/Coaxial Insulation Rating

12V, 300V, 600V Voltage Ratings Gas + Oil Resistant High Temperature

Sizing Wire

Choosing wire size: Signal wires carry little to no current and can be of a small

size. 22 Gauge is a common choice. Power wires that carry current should be sized based on

the maximum temperature rise you wish to have.▪ We have included in the hands-on packet a wire sizing guide based

on a specific portion of the National Electric Code. This is a very conservative table designed for residential wiring but is very commonly used. There are other tables available for specific applications.

▪ Wires get temperature rise from two sources▪ Direct current in the wire (resistive heating)▪ Induced current from other wires in the same raceway ▪ They will also get heat through heat transfer of other wires generating heat.

(oven effect)

▪ Duty cycle also factors into the required wire size. A low duty cycle load can use a smaller gauge wire than a high duty cycle load.

Using Wire and Raceways

Noise Signal to noise ratio + signal amplifiers Wires as antenna

Signal Wire Twisted Pair vs Non Twisted Pair Coax Crosstalk Shielding

Power Wire Route to avoid signals and interference Terminal blocks

Raceways + protection Conduit – rigid and flexible, plastic and metal Panduit and Wiremold Plastic/fiberglass loom Strain Reliefs Bending Radius

Connectors and Modular Design

Connectors are a vital component of modular design. They allow you to quickly and safely remove and replace

components or modules from your machine They allow for you to ensure proper polarity of your device

Connectors come in many shapes, sizes and ratings. These can be as simple as ring terminals on a barrier strip to more elaborate polarized locking connectors. Common connectors seen in ME 463▪ Berg Pins/Header Pins (used on sensors, Arduino boards)▪ Deans Connectors (batteries)▪ Tamiya connectors (batteries)▪ Ring Terminals/Spade Lugs▪ Screw Terminals

Make sure you have both sides to a connector!!!!! Make sure if you order a device, you order its connector as

well!!!!

Mounting Circuit Boards

Most electronic modules will be build on a Printed Circuit board that includes mounting holes. It is essential that the board/device be mounted securely. Standoffs are plastic/metal fasteners specifically designed to mount

circuit boards above a chassis component.▪ Plastic 4-40 thread stand offs are available for ME 463 from the E-shop

The back of most PCB are conductive and if shorted to the chassis or a moving part will cause electrical issues and damage. Take care to ensure the PCB is insulated and not in contact with your chassis

Additional though should be made with respect to connecting wiring to your devices when laying out your project. Allow adequate space for wires to route (bend Radius) Have proper connectors for wires Use tie straps to secure wiring into a harness and into your project

Batteries, Fuses and Master Disconnects

Batteries come in various types – Alkaline, Lithium Ion, NiCD, NiMh, Lead Acid Capacity is rated in Amp-Hours. Capacity also include max current draw

▪ Batteries should be sized based on run time needs as well as the maximum current draw required. Different battery types will have different max draws based on capacity.

Each type of battery requires a specific type of battery charger. Lithium batteries require a balancing charger and can/will explode if not charged/discharged correctly.

Fuses Protect batteries against short circuit or over current situations. Should be placed as close to the battery or power input as feasible in your

design. Come in ‘Fast blow’ and ‘slo-blow’ designs. Sized based on designed power

draw of your device Master Disconnects (Emergency Stops)

You should incorporate some type of disconnect for electrical power to your device

May be incorporated as part of a larger Emergency Stop system

Emergency Stop Systems

Any project with a significant hazard should implement an emergency stop system to render the machine ‘safe’

E-stop systems should De-energize any hazardous voltages or

electrical equipment that can cause motion. De-energize or disconnect any stored energy

sources such as pneumatic or hydraulic systems

Render safe any mechanical systems with stored energy (springs, suspended weights)

Emergency Stop Systems cont.

Emergency stop systems can be a simple switch or can be more elaborate systems with multiple switches and/or interlocks

As machines get more complicated, interlocks and emergency stops get more complicated. Include some type of diagnostics for where a fault

occurs Consider what may be faults and what may be

warnings Be sure to understand the sequence of operation

for you machine and work to understand and address all failure modes of your machine.

Designing and Documenting Circuits

Schematics and Wiring Diagrams

Schematics and Wiring diagrams are very similar in nature but not interchangeable.

A schematic is a pictorial representation of your circuit using standard symbols for components. Schematic’s can be used to create printed circuit

boards Symbols can be either US or International▪ Example – resistor is either a squiggly line or box

A Wiring Diagram or Wiring Layout is a picture of the connections you will make to the various modules and components in your device. A Wiring Diagram can be used to create wire harnesses

and to troubleshoot integration issues

Example Schematic - Inverter

This is a simple 12V DC to 120V AC inverter circuit schematic. This uses the ‘US’

style of symbols KiCAD is free

software and good choice for creating schematics

Example Wiring Diagram - Arduino

Fritzing is a free and popular software package for making wiring diagrams.

Example Schematic- Arduino

This is the schematic of the Arduino Wiring Diagram.

Instrumentation, Assembly and Troubleshooting

Troubleshooting

TEST AS YOU GO!!!!!!! When things fail, test independent components/modules Be Careful where you test – circuit boards will short if placed on metal chassis!!! Tools

Digital Multimeter (DMM)▪ Good for static voltage measurements

Ammeter▪ Measures current

Oscilloscope▪ Displays analog waveforms – good for seeing transient behavior

Counter▪ Counts pulses, displays frequency, duty cycle and other waveform attributes.

Logic Analyzer▪ Allows for seeing/decoding logic signals and protocol based signals. Useful for identifying timing

issues Common Pitfalls

Lack of a common Ground Exceeding rated output of devices (current drive capacity) Shorts/poor wiring technique during assembly Interference/crosstalk due to improper wire/shielding Improper mounting of components causing shorts

Digital MultiMeters (DMM)

2 Wire Measurements This is the common method most people are familiar with to

measure Voltage/Resistance 4 Wire Measurements

4 wire Measurements are used when the resistance of your device is so low that the resistance of the probe leads will cause error.

Sampling Error on AC signals – DMMs typically expect sinusoidal AC signals when in AC mode. They also use averaging or RMS methods for displaying the voltage it reads at any given time. Low frequency and high frequency AC signals may not read correctly. Use an Oscilloscope to view any time varying signals to ensure you get what you expect.

If making Current measurements, be sure to have a rough estimate of the current you will be measuring and ensure the DMM can handle that current. Blown fuses are common as well. If it exceeds the capacity – use a current shunt.

Oscilloscopes

Initial Settings, Timebase (Horizontal) should be set to around 1/frequency of your signal. Volts/Div (Vertical) should be about a quarter of your expected Vpp of your signal. You can then adjust the position dials to center your signal. Once you have found your signal, adjust timebase and V/div as needed.

Be cautious using ‘autoscale’ buttons. These may or may not show you your signal. If there is a connection problem with your signal, you will see noise

Triggering can be used to ‘stop’ the waveform of your signal. Triggering can be internal (rising edge/falling edge) of your signal or external and typically has a level adjustment.

You should use properly matched scope probes to measure small signals. Coaxial cables may load your signal and display distorted signals.

The Ground of the Scope probe is connected to GROUND. If this is connected to a terminal other than ground of a power supply or output, it will short that connection to ground which likely will result in damage to the probe and/or your device.

Prototyping Boards

Breadboards Breadboards are for testing simple circuits on the bench. Breadboards

have no place in the actual prototype itself. Perfboard

Perfboard is the cheapest and most flexible. This is also the most difficult type of board to assemble a circuit cleanly.

Solderboards Solderboards are perfboards that have plating on one side bridging holes.

This plating also makes it possible to solder components to the board. Printed Circuit Boards (PCB)

These are boards that are custom made with your circuit traces embedded in the copper. This is the type of board you will be assembling in the hands on session.

PCB boards can use surface mount components and be made to odd sizes.

We have a LPKF Circuit Board Fabrication center that will allow you, as an ME student, to create your own custom PCB. See the E-shop for access and details.

Basics of Soldering - Components

Through Hole Components Typical components found in the EE201 kits Easiest of the components to solder

Surface Mount Components Think of an computer board/arduino Much more difficult to assemble, usually

requires a printed circuit board May require special techniques and

equipment▪ Reflow soldering▪ Hot air soldering

Basics of Soldering

Required Equipment Soldering iron, ideally adjustable Solder, rosin core 60/40 mix. NOT ACID CORE Sponge, moist – to clean tip of iron Wire Cutters/Diagonal Cutters

Basic Technique Heat the joint, not the solder Think about assembly order before you start. Use jigs/vises/holders whenever needed Think about amount of heat applied. Ensure you manage this to

avoid damaging sensitive components Cold Solder Joints

Connection that is soldered but does not fully bond the two components physically and electrically. Generally causes device not to work.

Cold Solder Joints

Next Step – We build a circuit!Be sure to come to your hands-on session!