MECH 400 Underwater Glider Design Project May 20, 2008MECH 400 Tips and Tricks1.

May 20, 2008 MECH 400 Tips and Tricks 1

MECH 400Underwater Glider Design Project


Introduction

1.) Major electrical pitfalls from previous years• Electrostatic Discharge• Wiring• Noise• Grounding

2.) OOPic basics• Common Blunders• Variables and OOPic Math• Pulse Width Modulation• Events, Virtual Circuits and Gates


Electrical Tips


Shady Wiring Practices & ESD

Damaged equipment: $$ comes out of your own pocket


Electrostatic Discharge (ESD)

• Electro-static discharge– Sources: carpets, other types of floor, chairs in the

Fluids lab!!!– Use a suitable workspace, keep food/drink far from

your work

http://mfrost.typepad.com/.shared/image.html?/photos/uncategorized/bcweaves.jpg


Electrostatic Discharge (ESD)Preventative Measures• Wear a $5 ground-strap (with 1MΩ resistor)• Use a grounded working surface, or clip on to a power supply chassis• Please ask your TA how to set this up, if you are unsure or worried

about electrical shock!!!!

USE MIDDLE PRONG ONLY


Creative Wiring 101

• Do it right the first time, do it once– Do it wrong: happy hunting

• Remember wires have mass, and occupy space!!!

• Last year– One group’s AUV didn’t make it in the water due to

creative wiring. They were trouble-shooting on the side of the pool until they ran out of time


Creative Wiring 101


Creative Wiring 101

• Use solder to make a firm connection

• Use shrink wrap to avoid shorts

• Use cable ties to organize or bundle


Grounding

• Proper grounding is essential to reduce noise– Cause for many problems last year

• Put a capacitor between power and ground to minimize the AC noise

• Avoid ground loops – This is where two grounding points have different

potential – Use a central grounding point – don’t daisy chain your

grounds• Use caution with power leads and chassis ground


Electrical Noise/Disturbances

• All circuits are subject to environmental and local noise– Sources: MOTORS, 60 Hz

• Typical mistakes

– Circuits work fine until the system is combined– Long wire runs collect noise– Improper grounding


Reduce noise by proper shielding– How do you shield? – don't solder the shield

at both ends • This creates a parallel

circuit, commonly known

as a ground loop. • this will make the

problem worse! – The shield will attach to the same connection point as

the ground. – Antenna principal: the shield acts as an antenna for

noise – you don’t want to be feeding the noise into your sensor.


OOPic Basics


Common OOPic/Speed Controller Blunders

– Hooking the 9V battery up backwards • NO reverse polarity protection on the OOPic

– Hooking up the speed controller signal pins backwards to the power pins on the OOPic

– Don’t use more power than devices are rated for


OOPic & Speed Controllers

• All documentation is online at www.oopic.com– Pseudo C, and some tutorials

• Try figuring it out first, but ask if you don’t understand


OOPIc Troubleshooting

• Know these steps!• Problems uploading programs, or no response

1) Serial cable screwed into ports?

2) Check 9V power supply

3) Check voltage regulator for 5V output

4) Check EEPROM is seated properly

5) …and if all else fails


OOPic Troubleshooting: if all else fails

• 5) Last ditch effort for OOPIc-R – Reset EEPROM– Power OFF OOPic– Remove the EEPROM chip CAREFULLY!!!!– Power the board back up w/o the EEPROM chip– Start download of program– IDE will tell you that there is no EEPROM and will ask

you to reinstall it• Make sure it is installed the proper direction (little

dot is pin 1)• KEEP POWER ON

– Install the EEPROM and click OK


Using Variables on the OOPIC

• Signed versus Unsigned– 16 bit variables: oInt is signed

oWord is unsigned– 8 bit variables: oChar is signed

oByte is unsigned• When you define an object be careful to look whether it

is expecting a signed or unsigned value for the inputs or outputs.

• Signed numbers use a 2’s Complement Representation i.e. -x= (2N-x)


Mathematics on the OOPIC

• There are not provisions for doing signed math on the OOpic.

• Addition and Subtraction will still work with 2’s complement numbers.

• Multiplication and division of signed values can be handled by multiplying or dividing positive values (equivalent to unsigned) and then adjusting the sign of the result. For example: A* ( - B) = - (A * B).


Pulse Width Modulation


Pololu Speed Controller

• 2 Channel, 16 V Max input voltage + protection• Things to note:

– Two IO Lines + PWM channel per motor– Will have to make a cable (simple)

• The added benefit of reliability from these speed controllers is worth the additional wiring hassle


OOPic & Speed Controllers

• Documentation regarding driver connections are online on the OOPic website


Polling vs. “Interrupt” style

• What is polling?• What is an interrupt?• e.g. teacher checking for hand to raise

– Polling: teacher checks each person to see if their hand is raised

– Interrupt driven: class manager informs teacher when someone’s hand is up


Real Time Systems and Polling


Using Event Detection


OEvent Features

• oEvents can be prioritized– See oEvents on the online manual– By default all events have equal priority

• BE CAREFUL: real time systems are a pain to debug!• Do yourself a favor - make a nice flow chart!


Event Programming


oEvents and Logic Gates

• Powerful OOpic Objects that can be used with events


Questions?

• Be prepared for lab demos• Don’t debug during demo

• Persons requiring a basic run down or more information regarding the OOPic operation can stay behind and ask questions

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MECH 400 Underwater Glider Design Project May 20, 2008MECH 400 Tips and Tricks1.

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