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Practical Design I/O Circuits Electronic Circuitry between the low power “control electronics” and the input and output devices. prepared by Prof. George Slack (EE) Copyright © 2006 Rochester Institute of Technology All rights reserved. EDGE™ What are the key considerations? • Bandwidth, frequency response, rf to dc • Impedance matching • • • • Low Voltage to High Current Low Voltage to High Voltage Low Current to High Current Low to Current to High Voltage • Circuit protection electronics – Surge protection techniques – Debugging can become somewhat frantic with a potential for shorting or over powering. Though electronic devices may be inexpensive, the re-ordering time and re-soldering takes time. EDGE™ When is this needed? • Senior Design I – Phase 3 Detail Design wks 5-11 – Phase 1 Concept Development wks 3-7 • Lab feasibility "Fail Often, Fail Fast, Fail Cheap" – (i.e. evaluation, characterization, shortfalls) • Senior Design II – Pre-integration testing with lab equipment DUT (device under test). Wks 3- 6 EDGE™ Engineering Specifications 1. Review various manufactures specification sheets when considering output devices. 2. Timing of data, enables, select lines, etc. 3. Current (i.e. CMOS versus TTL ) needs, sink, source or both Vdd/Vcc 4. Control Voltage (Vdd vary from 1.5 VDC to 12 VDC typically) 5. Frequency Response 6. Heat and EMI Noise 7. Apply to Thevenin Equivalent Circuits – Source electronics – Device being driven – RLC loads (& potential for dangerous current and voltage spikes) EDGE™ Engineering Specification Sheets 1. Manufacturer’s Home Pages 2. Suppliers: DigiKey, Mouser and Allied offer good on-line spec sheets 3. http://www.findchips.com/ 4. http://cmpmedia.globalspec.com/ 5. Google 6. RIT Library services 7. Microcontroller or device evaluation/ demo kits 8. http://www.esacademy.com/automation /faq/primer/6.htm EDGE™ Manufacturer’s 1. Specification Sheets 2. Application Notes Save Hours of design time! Exploit their Design Notes! • MicroController Interface needs to protect electronics. • Many Specification Sheets have recommended applications that may apply directly to your design! Use them! • Example 1. PIC18F2455 Interface considerations – See attached pdf. • Example 2. Freescale Semiconductor Inc - application schematic – Motor Controller MC3PHACVDW EDGE™ Output Circuits • Logic: Microcontroller to input of electronics drivers. • Driver: (voltage to voltage, voltage to current.) • Device: – – – – – – Motors, Linear Actuators Solenoids Storage Capacitors HVPS LEDs Heaters EDGE™ Types of Drive Components Impedance matching: • Op Amps • Optical devices • Transistors: Single stage and Darlington. • JFETs • MOS FET • IGBT DC to AC inverters (hybrid cars, mass transit) EDGE™ Specific Applications: • • • • • H bridge – DC Motors Optical Isolators- Power Supply Separation Optical Drivers Fiber Optics and Fiber Optics I/0 Devices DC to DC converters – voltage boasting/ ± polarity – current boasting EDGE™ Practical Design Considerations • Too often the interfaces are not considered until Senior Design II once integration begins. – DO IT NOW and order your “debug” supplies along with your other components. • • • • • Passive Devices: Harnesses (& cables) connectors Test points Discrete LEDs • • • • • • Active Devices: Interface Devices Power On/Off, Reset and Safety Switches Power Reset Switch, Sample Select Switch USB, RS232, Ethernet (may not need the form factor) Accessory power connectors Removable AC power cord EDGE™ Practical Harness Considerations 1. 2. Current, Voltage Needs • Gauge of wire, insulation • • • Connect/ disconnect needs Routing, protecting Mounting, vibration and stability • Instrumentation quality for long life Use and Abuse • 3. 4. Gold versus Tin; environment, corrosion, current rating Color Coding for ease in Debug and future use. As an example; 1. Red Vcc/Vdd 2. Black Grd/ Vss 3. Org for signal Fabricating: Harness board and nails EDGE™ Example of Driver Circuit •• Driver Circuit – Opto 22 ODC5 – See diagram below for application. – Output Device – 2.5a, 50 vdc Inductive Load EDGE™ BOM misc: Connectors/ Pins Add all needed I/O connectors to your schematic(s). 1. Connect/ disconnect needs – screw terminators, push type 2. Major Manufactures: Amp, Molex 3. Location – – – between assemblies interface to other projects (collaborate with other teams) instrumentation 4. Get crimp compatibility to pin manufacturers (style and gauge). 5. Pins: crimp versus solder 6. Current rating rule of thumb is 10x. i.e. 100 ma purchase 1 amp pins 7. Types; ribbon, D shell, PCB mount EDGE™ H Bridge Considerations • Motors or whenever you need to direct current. • Introduction to H bridge operation: – http://www.dprg.org/tutorials/1998-04a/ • Designing an H-Bridge and PWM Circuits and Code – http://www.learn-c.com/experiment7.htm • Debugging: Initial reset may close a short circuit or stress on the H bridge. Symptom: Motor shaft may pulse or flinch at power on. May cause immediate failure. • Design Needs: Inductive loads and protection diode. EDGE™ Rochester source • On-line: Digi-Key, Mouser, Allied, … • When you want to look at what you are buying: http://www.glenwoodsales.com/ GLENWOOD SALES COMPANY 594 HAGUE STREET ROCHESTER, NEW YORK 14606 USA Tax free with RIT PO (contract Chris Fisher for form) EDGE™