Presentation Transcript

1. School of Mechanical Engineering

   Electronics Fabrication and Assembly Workshop

2. 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 Understanding of Motor types and Motor Controllers Understanding of Electronics Sensors Understanding of types of wire and wire routing Understanding Fuses and Emergency Stops
3. Objectives continued More Objectives: 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!
4. Transmitting Information Signal types and Noise
5. 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 PWM (Pulse Width Modulated) signal Square wave, variable duty cycle Serial, Ethernet, GPIB, CAN Negotiated Protocols for sending data
6. Analog Signal – 0-10V
7. Digital Signal - TTL
8. Current Signal – 4mA – 20mA
9. PWM Signal
10. 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.
11. 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.
12. Noise and Signal to Noise RatioSignal and Noise with similar Vpp and average DC level
13. 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.
14. Noise and Signal to Noise RatioSignal and Noise with similar Vpp but different average DC level
15. 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 signal remains similar to the magnitude of the ambient noise, our total signal is not representative of the desired signal
16. Noise and Signal to Noise RatioSignal and Noise with different Vpp and different average DC level
17. 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
18. Demo – Crosstalk and Noise Demo: Noise injected from a single wire to parallel wires of different types over a length of 6 feet.
19. Type of Hardware Electronics Components and Modules
20. 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
21. 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) Emitter Collector Base
22. Transistors, MOSFET MOSFET may also be called power transistors due to the capability to handle large currents. 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)
23. 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
24. 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?
25. 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
26. 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!
27. Common Interface Devices/Modules Transistor Current Amplifier Module Used to take a low current drive output from Microcontroller and turn on a solenoidor 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)
28. 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
29. Demo – Switch Debouncing Demo – Impulse Count for a single closure of a mechanical switch
30. 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
31. 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
32. 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 Each type 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
33. Emergency Stop Systems Any project with a significant hazard should implement an emergency stop systemto 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)
34. 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.
35. Instrumentation, Assembly and Troubleshooting
36. Troubleshooting TEST AS YOU GO!!!!!!! When things fail, test independent components/modules 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
37. 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 – DMM’s 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.
38. 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.
39. 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.
40. 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
41. 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.
42. Cold Solder Joints
43. Next Step – We build a circuit!