Transcript se3910-2-1-BasicCircuitsAndHardwareInterruptsx

SE3910
Week 2, Class 1
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Today
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Tomorrow
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Basic Circuits
Other ???
Lab 2, S365 (Complete prelab BEFORE)
Thursday
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See Schedule
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Slide design: Dr. Mark L. Hornick
Content: Dr. Hornick
Errors: Dr. Yoder
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Warning…
Originally from:
http://www.thegooglestory.com/glat.html
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Cartoon
One source: http://www.sengpielaudio.com/calculat
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Equipment (Reminder)
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This week: Purchase 4GB or greater micro
SD card
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Used Lab 3
(Optional) Tools – e.g. needle-noise pliers
Check out short-term
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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
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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
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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
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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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Warning 2: (Low risk)
LEDs have constant voltage
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
Solution 2: Use limiting resistor
Use a limiting resistor to fill up the rest of the
voltage and set current.
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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.
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Slide design: Dr. Mark L. Hornick
Content: Dr. Hornick
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Solution 3:
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Do not place beaglebone on metal surface
(e.g. aluminum-finish laptop) [EB, p. 21]
Ensure beaglebone is correctly configured
before powering
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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.
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Warning 4: (High risk)
Beaglebone is 3.3 V
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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:
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Always use the 3.3 V supply
Never use external power – use the 3.3 V
supplied
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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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Warning 5: (Medium risk)
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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
Solution 5:
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Hold down power button until all lights turn off
If you must, hold down reset button (which
forces the bone off) while unplugging.
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Warning 6: Hard to pick the
right pin
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You can, e.g. easily plug into 5V when you
mean to plug in to 3.3V.
Solution 6:
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Print labels for your pins
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Use the breakout cape
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tiny.cc/ebb105 [EB, p. 21]
It has labels already printed
Google beaglebone black pinout
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Slide design: Dr. Mark L. Hornick
Content: Dr. Hornick
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Warning 7: Analog limit
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No more than 1.8 V into analog pin
Solution 7:
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Use the supplied 1.8 V supply as power for
analog devices
Ensure devices are not configured in analog
before plugging into POTENTIALLY analog
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pins
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Slide design: Dr. Mark L. Hornick
Content: Dr. Hornick
Warning 8: Don’t pull SD card
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If you pull out the card, it could cause
damage
Solution 8:
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Push in the card, and it will push itself out
(never fails…)
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Slide design: Dr. Mark L. Hornick
Content: Dr. Hornick
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Warning 9: Other things
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If you are working on a very complicated
circuit, please see the (un)official System
Reference Manual
Solution
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And read all the red text
(I have a summary file, if you want …)
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Slide design: Dr. Mark L. Hornick
Content: Dr. Hornick
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GPIO safety (summary of a few
key points)
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Sourcing limit: 4mA
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Sinking limit: 8mA
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Limit if current is coming OUT OF Beaglebone
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 Yoder
Slide style: Dr. Hornick
Much Material: Dr. Schilling
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References
EB: Derek Malloy, Exploring Beaglebone,
Wiley, 2015
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Slide design: Dr. Mark L. Hornick
Content: Dr. Hornick
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