SE3910Week 2, Class 1 Today

Basic Circuits Other ???

Tomorrow Lab 2, S365 (Complete prelab BEFORE)

Thursday See Schedule

SE-2811Slide design: Dr. Mark L. Hornick

Content: Dr. HornickErrors: Dr. Yoder

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Warning…

Originally from: http://www.thegooglestory.com/glat.html

http://xkcd.com/356/SE-2811Dr.Yoder 2

Cartoon

One source: http://www.sengpielaudio.com/calculator-ohmslaw.htm

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Equipment (Reminder)

This week: Purchase 4GB or greater micro SD card Used Lab 3

(Optional) Tools – e.g. needle-noise pliers Check out short-term

Kit (breakout board, breadboard cape, LCD cape, USB Oscilloscope)

Small parts (also may desire to purchase)

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Ex: Compute voltage across C1

If S1 is closed, and S2 is opened, what is the voltage across C1?

If S2 is closed, and S1 is opened?

If both are opened? If both are closed?

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Ex: Compute voltage into GPIO

If S1 is open and S2 is closed, compute the voltage from GPIO 12 to ground.

(Assume GPIO 12 is not connected to anything)

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A slightly better assumption if connected to a GPIO input

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Warning 1: (Low risk)Input is like a (very small) capacitor Modern processors use CMOS technology These gates can look something like this on

the inside:

If left “floating,” can be any voltage If two switches use, can short source, so …

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Solution 1: Use a pull-up or pull-down resistor

(This is from Lab 2, you

will analyze it there.)

( (See pp. 137-138 in E Exploring Beaglebone b by Derek Molloy, . 2015)

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If you apply 3.3 V to a 2.10 V LED, it will be like applying 1.2 V directly to a short circuit

Use a limiting resistor to fill up the rest of the voltage and set current.

Warning 2: (Low risk)LEDs have constant voltage

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Solution 2: Use limiting resistor

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Warning 3: (High risk)

Do not short the GPIO pins to ground or 3.3V when they are in output mode.

SE-2811Slide design: Dr. Mark L. Hornick

Content: Dr. HornickErrors: Dr. Yoder

Solution 3:

Do not place beaglebone on metal surface (e.g. aluminum-finish laptop) [EB, p. 21]

Ensure beaglebone is correctly configured before powering If circuit provides input, beaglebone MUST NOT

provide output When using output, your circuit should not

Source more than 4mA (current out of bone) Sink more than 8mA (current into bone)

… for any given GPIO pin.SE-2811Dr.Yoder 12

Warning 4: (High risk)Beaglebone is 3.3 V

Supplying 5 V to any GPIO pin could damage it.

Furthermore, supplying even 3.3 V to a pin without powering the board could damage it.

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Solution 4:

Always use the 3.3 V supply Never use external power – use the 3.3 V

supplied Unless you know what you are doing! May need to use voltage converters from external

signals. Or at least external logic “enabled” by the 3.3V

supply

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Do not unplug beaglebone while running Residual currents can result in higher

residual voltages Memory might be saved in inconsistent state

Hold down power button until all lights turn off If you must, hold down reset button (which

forces the bone off) while unplugging.

Warning 5: (Medium risk)

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Solution 5:

You can, e.g. easily plug into 5V when you mean to plug in to 3.3V.

Print labels for your pins tiny.cc/ebb105 [EB, p. 21]

Use the breakout cape It has labels already printed

Google beaglebone black pinout

Warning 6: Hard to pick the right pin

SE-2811Slide design: Dr. Mark L. Hornick

Content: Dr. HornickErrors: Dr. Yoder

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Solution 6:

No more than 1.8 V into analog pin

Use the supplied 1.8 V supply as power for analog devices

Ensure devices are not configured in analog before plugging into POTENTIALLY analog pins

Warning 7: Analog limit

SE-2811Slide design: Dr. Mark L. Hornick

Content: Dr. HornickErrors: Dr. Yoder

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Solution 7:

If you pull out the card, it could cause damage

Push in the card, and it will push itself out (never fails…)

Warning 8: Don’t pull SD card

SE-2811Slide design: Dr. Mark L. Hornick

Content: Dr. HornickErrors: Dr. Yoder

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Solution 8:

If you are working on a very complicated circuit, please see the (un)official System Reference Manual

And read all the red text (I have a summary file, if you want …)

Warning 9: Other things

SE-2811Slide design: Dr. Mark L. Hornick

Content: Dr. HornickErrors: Dr. Yoder

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Solution

GPIO safety (summary of a few key points)

Sourcing limit: 4mA Limit if current is coming OUT OF Beaglebone

Sinking limit: 8mA Limit if current is flowing INTO Beaglebone

Digital Voltage: 3.3 V Analog input max voltage: 1.8 V

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Ex: What is the resistance of this resistor?

SE-3910 - Dr. Josiah YoderSlide style: Dr. Hornick

Much Material: Dr. Schilling21

References

EB: Derek Malloy, Exploring Beaglebone, Wiley, 2015

SE-2811Slide design: Dr. Mark L. Hornick

Content: Dr. HornickErrors: Dr. Yoder

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