Transcript Cal(IT)2

Lab 5 – Power/Energy
Larry, Ravi
What will be discussed today
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What is Power?
What is Energy?
A Real World Example
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Why do we care?
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ATMega328p Demo Setup
ATMega328p Interactive Demo
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Low Power Wireless Communication Methodologies
ATMega328p & Xbee Demo Low Power Wireless Demo
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Summary
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Questions
What is Power?
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Physic’s Definition:
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Electric Power:
2
V
P  IV  I 2 R 
R
– Using Ohm’s Law, we can get the other forms
– What is the SI unit for power?
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Examples:
– What is the power dissipated
through the 100Ohm resistor?
What is Energy?
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Physic’s Definition
– Power definition again:
– Definition of work (Energy):
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Mechanical Definition:
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Electric Definition:
E=
ò P(t)dt = ò i(t)v(t)dt = IV(t
end
- tstart )
T
– What is the SI unit for energy?
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Examples
– Circuits in previous slides run for 1 minutes
How much energy was dissipated through resistor?
– What is the Ah in the iphone
battery?
A Real World Example
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ZeroTracer[1]
– ~750W = 1HP
– What is the Amp-hour of the battery?
– What is the charge current of the 9.9KW charger?
Why do we care?
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HydroWatch Berkeley[2]
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Low power
Self-charging
Ultra Low maintenance
Runs forever
Home power consumption monitoring
– Has to be low power otherwise monitoring is not useful
ACME module[3]
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Helps enable your smartphone to
run for a day without recharging
Extend Battery life
Discharge graph
of NCR18650
Cells[4]
Demo Setup
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Circuit layout
– ATmega328P instead
of ATmega88PA
– 10x 1000uF Caps in
parallel as C1
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Capacitors as Simulated battery
– Energy stored in Capacitor
[5]
1
W = CV 2
2
– What is the energy stored in our capacitors assuming 5V DC supply in our
circuit?
– Given the energy above, what is nominal Ah?
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Serial Communication at 9600 baudrate externally powered
– We are only concerned about how long will the ATmega328P be able to
generate the TX signal
Atmega328P background
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8Mhz internal Calibrated RC Clock
128Khz internal RC Clock
1.8V-5.5V Operating voltages
Low Power Consumption
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On Right is the Block Diagram
ATmega328P
Datasheet[6]
ATMega328P Power Demo
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Overall Goals:
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Take ADC
Do 1000 statement processing
Transmit something over UART
Wait 1 sec
Repeat
Power Optimization Steps
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I – No Optimization
– 8Mhz Clock
– BOD (Brown Out Detection) = 2.7V
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II – Turn off things we don’t need and change IOs
– Same as I
– Turn off SPI/I2C/Timers/etc
– Make all IOs as inputs and pull-up (see datasheet on why)
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III – Slow down the clock
– Same as II
– Slow clock to 1 Mhz
– BOD = 1.8V because we are using only 1Mhz (see datasheet)
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IV – Sleep while waiting
– Same as III
– Turn off ADC when not being used
– Setup interrupt to wake up after 1 sec
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Other Optimization?
Atmega328P background followup
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Atmega328P power mode:
– Why do we use Power-save mode?
Power Optimization Performance
Optimization
Number of seconds
before shutdown
% change
I
4 seconds
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II
5 seconds
25% increase from I
III
14 seconds
180% increase from II
IV
>200 seconds
> 14000% increase from III
Low Power Wireless Communication Methodologies
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Adjust power base on distance from objects
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Send only when necessary, i.e. save data and then send all at once
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Send as fast as possible and then go to sleep
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Synchronized listening cycle, i.e. wake, listen, and transmit for 1 sec then go
to sleep for 1 sec.
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Use error correction that does not require resubmission of data
Tolerate error in data (TCP vs UDP)
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Use Multi-hop network
ATMega328p & Xbee Demo Low Power Wireless
Demo
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Notice the low “On” state so power consumption is minimized
Summary
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Talked about Power
– P=IV
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Talked about Energy
E=
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ò P dt
Gave a real world example of Power/Energy
– ZeroTracer
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Why low power is important
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ATMega328P Demo
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Low Power communication methodologies
– Send when you can, etc
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Xbee Demo
Questions/Comments?
References
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[1] - http://www.zerotracer.com
[2] http://www.cuahsi.org/pageFiles/CUAHSI%20Cyberseminar%20Bode%20Fin
al.pdf
[3] - http://acme.cs.berkeley.edu
[4] - http://industrial.panasonic.com/wwwdata/pdf2/ACA4000/ACA4000CE240.pdf
[5] - http://www.atmel.com/Images/doc8349.pdf
[6] - http://www.atmel.com/Images/Atmel-8271-8-bit-AVR-MicrocontrollerATmega48A-48PA-88A-88PA-168A-168PA-328-328P_datasheet.pdf