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Electronic Circuitry between the low power “control electronics” and the input

and output devices.

prepared by Prof. George Slack (EE)prepared by Prof. George Slack (EE)

Copyright © 2006 Rochester Institute of TechnologyAll rights reserved.

Practical Design Practical Design I/O CircuitsI/O Circuits

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What are the key considerations?What are the key considerations?

• Bandwidth, frequency response, rf to dcBandwidth, frequency response, rf to dc• Impedance matchingImpedance matching

• Low Voltage to High CurrentLow Voltage to High Current• Low Voltage to High VoltageLow Voltage to High Voltage• Low Current to High CurrentLow Current to High Current• Low to Current to High VoltageLow to Current to High Voltage

• Circuit protection electronics Circuit protection electronics – Surge protection techniquesSurge protection techniques– Debugging can become somewhat frantic with a Debugging can become somewhat frantic with a

potential for shorting or over powering. Though potential for shorting or over powering. Though electronic devices may be inexpensive, the re-ordering electronic devices may be inexpensive, the re-ordering time and re-soldering takes time.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""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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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/Vcc4. Control Voltage (Vdd vary from 1.5 VDC to 12

VDC typically) 5. Frequency Response6. Heat and EMI Noise7. Apply to Thevenin Equivalent Circuits

– Source electronics– Device being driven– RLC loads (& potential for dangerous current

and voltage spikes)

Engineering Specifications

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Engineering Specification Sheets

1. Manufacturer’s Home Pages2. Suppliers: DigiKey, Mouser and Allied

offer good on-line spec sheets3. http://www.findchips.com/ 4. http://cmpmedia.globalspec.com/5. Google6. RIT Library services

7.7. Microcontroller or device evaluation/ Microcontroller or device evaluation/ demo kits demo kits

8. http://www.esacademy.com/automation/faq/primer/6.htm

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Manufacturer’s Manufacturer’s 1. Specification Sheets1. Specification Sheets

2. Application Notes2. Application NotesSave Hours of design time!Save Hours of design time!Exploit their Design Notes!Exploit their Design Notes!

• MicroController Interface needs to protect electronics.MicroController Interface needs to protect electronics.• Many Specification Sheets have recommended Many Specification Sheets have recommended

applications that may apply directly to your design! Use applications that may apply directly to your design! Use them!them!

• Example 1. PIC18F2455 Interface considerationsExample 1. PIC18F2455 Interface considerations– See attached pdf.See attached pdf.

• Example 2. Freescale Semiconductor Inc - application Example 2. Freescale Semiconductor Inc - application schematicschematic– Motor Controller MC3PHACVDWMotor Controller MC3PHACVDW

Acrobat Document Acrobat Document

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Output CircuitsOutput Circuits

• LogicLogic: Microcontroller to input of : Microcontroller to input of electronics drivers.electronics drivers.

• DriverDriver: (voltage to voltage, voltage to : (voltage to voltage, voltage to current.)current.)

• Device:Device: – Motors, Linear ActuatorsMotors, Linear Actuators– SolenoidsSolenoids– Storage CapacitorsStorage Capacitors– HVPSHVPS– LEDsLEDs– HeatersHeaters

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Types of Drive ComponentsTypes of Drive Components

Impedance matching: Impedance matching: • Op AmpsOp Amps• Optical devicesOptical devices• Transistors: Single stage and Darlington.Transistors: Single stage and Darlington.• JFETsJFETs• MOS FET MOS FET • IGBT DC to AC inverters (hybrid cars, mass IGBT DC to AC inverters (hybrid cars, mass

transit)transit)

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Specific Applications:Specific Applications:

• H bridge – DC MotorsH bridge – DC Motors• Optical Isolators- Power Supply SeparationOptical Isolators- Power Supply Separation• Optical DriversOptical Drivers• Fiber Optics and Fiber Optics I/0 DevicesFiber Optics and Fiber Optics I/0 Devices• DC to DC convertersDC to DC converters

– voltage boasting/ ± polarityvoltage boasting/ ± polarity– current boastingcurrent boasting

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• 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

Practical Design Considerations

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Practical Harness Considerations

1. Current, Voltage Needs• Gauge of wire, insulation

2. Use and Abuse • Connect/ disconnect needs • Routing, protecting• Mounting, vibration and stability• Gold versus Tin; environment, corrosion, current rating• Instrumentation quality for long life

3. Color Coding for ease in Debug and future use.As an example;1. Red Vcc/Vdd2. Black Grd/ Vss3. Org for signal

4. Fabricating: Harness board and nails

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Example of Driver CircuitExample of Driver Circuit

•

Acrobat Document

• Driver Circuit – Opto Driver Circuit – Opto 22 ODC522 ODC5– See diagram below See diagram below

for application.for application.– Output Device – 2.5a, Output Device – 2.5a,

50 vdc Inductive Load50 vdc Inductive Load

Acrobat Document

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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, Molex3. 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 solder6. Current rating rule of thumb is 10x. i.e. 100 ma

purchase 1 amp pins7. Types; ribbon, D shell, PCB mount

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H Bridge ConsiderationsH Bridge Considerations

• Motors or whenever you need to direct current.Motors or whenever you need to direct current.• Introduction to H bridge operation:Introduction to H bridge operation:

– http://www.dprg.org/tutorials/1998-04a/http://www.dprg.org/tutorials/1998-04a/

• Designing an H-Bridge and PWM Circuits and Code Designing an H-Bridge and PWM Circuits and Code – http://www.learn-c.com/experiment7.htmhttp://www.learn-c.com/experiment7.htm

• Debugging: Initial reset may close a short circuit Debugging: Initial reset may close a short circuit or stress on the H bridge. Symptom: Motor shaft or stress on the H bridge. Symptom: Motor shaft may pulse or flinch at power on. May cause may pulse or flinch at power on. May cause immediate failure.immediate failure.

• Design Needs: Inductive loads and protection Design Needs: Inductive loads and protection diode.diode.

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Rochester sourceRochester source

• On-line: Digi-Key, Mouser, Allied, …On-line: Digi-Key, Mouser, Allied, …

• When you want to look at what you are When you want to look at what you are buying:buying:http://www.glenwoodsales.com/http://www.glenwoodsales.com/

GLENWOOD SALES COMPANYGLENWOOD SALES COMPANY594 HAGUE STREET594 HAGUE STREETROCHESTER, NEW YORK 14606 USAROCHESTER, NEW YORK 14606 USA

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