Transcript Practical Design I/O Circuits Electronic Circuitry between the low power “control electronics” and the input and output devices. prepared by Prof.

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.
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What are the key considerations?
• Bandwidth, frequency response, rf to dc
• Impedance matching
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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.
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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
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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)
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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
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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
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Output Circuits
• Logic: Microcontroller to input of electronics
drivers.
• Driver: (voltage to voltage, voltage to
current.)
• Device:
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Motors, Linear Actuators
Solenoids
Storage Capacitors
HVPS
LEDs
Heaters
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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)
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Specific Applications:
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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
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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.
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Passive Devices:
Harnesses (& cables)
connectors
Test points
Discrete LEDs
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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
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Practical Harness Considerations
1.
2.
Current, Voltage Needs
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Gauge of wire, insulation
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Connect/ disconnect needs
Routing, protecting
Mounting, vibration and stability
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Instrumentation quality for long life
Use and Abuse
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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
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Example of Driver Circuit
•• Driver Circuit – Opto
22 ODC5
– See diagram below for
application.
– Output Device – 2.5a,
50 vdc Inductive Load
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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
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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
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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.
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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)
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