Lab 5 – Power/Energy Larry, Ravi

What is Power? What is Energy? A Real World Example Why do we care? ATMega328p Demo Setup ATMega328p Interactive Demo Low Power Wireless Communication Methodologies ATMega328p & Xbee Demo Low Power Wireless Demo Summary Questions What will be discussed today

What is Power? Physic’s Definition: Electric Power: –Using Ohm’s Law, we can get the other forms –What is the SI unit for power? Examples: –What is the power dissipated through the 100Ohm resistor?

What is Energy? Physic’s Definition –Power definition again: –Definition of work (Energy): Mechanical Definition: Electric Definition: –What is the SI unit for energy? Examples –Circuits in previous slides run for 1 minutes How much energy was dissipated through resistor? –What is the Ah in the iphone battery?

ZeroTracer[1] –~750W = 1HP –What is the Amp-hour of the battery? –What is the charge current of the 9.9KW charger? A Real World Example

Why do we care? HydroWatch Berkeley[2] –Low power –Self-charging –Ultra Low maintenance –Runs forever Home power consumption monitoring –Has to be low power otherwise monitoring is not useful Helps enable your smartphone to run for a day without recharging Extend Battery life ACME module[3] Discharge graph of NCR18650 Cells[4]

Demo Setup Circuit layout –ATmega328P instead of ATmega88PA –10x 1000uF Caps in parallel as C1 Capacitors as Simulated battery –Energy stored in Capacitor –What is the energy stored in our capacitors assuming 5V DC supply in our circuit? –Given the energy above, what is nominal Ah? Serial Communication at 9600 baudrate externally powered –We are only concerned about how long will the ATmega328P be able to generate the TX signal [5]

Atmega328P background 8Mhz internal Calibrated RC Clock 128Khz internal RC Clock 1.8V-5.5V Operating voltages Low Power Consumption On Right is the Block Diagram ATmega328P Datasheet[6]

Overall Goals: –Take ADC –Do 1000 statement processing –Transmit something over UART –Wait 1 sec –Repeat ATMega328P Power Demo

I – No Optimization –8Mhz Clock –BOD (Brown Out Detection) = 2.7V 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) III – Slow down the clock –Same as II –Slow clock to 1 Mhz –BOD = 1.8V because we are using only 1Mhz (see datasheet) IV – Sleep while waiting –Same as III –Turn off ADC when not being used –Setup interrupt to wake up after 1 sec Other Optimization? Power Optimization Steps

Atmega328P background followup Atmega328P power mode: –Why do we use Power-save mode?

Power Optimization Performance OptimizationNumber of seconds before shutdown % change I4 seconds--- II5 seconds25% increase from I III14 seconds180% increase from II IV>200 seconds> 14000% increase from III

Low Power Wireless Communication Methodologies Adjust power base on distance from objects Send only when necessary, i.e. save data and then send all at once Send as fast as possible and then go to sleep Synchronized listening cycle, i.e. wake, listen, and transmit for 1 sec then go to sleep for 1 sec. Use error correction that does not require resubmission of data Tolerate error in data (TCP vs UDP) Use Multi-hop network

ATMega328p & Xbee Demo Low Power Wireless Demo Notice the low “On” state so power consumption is minimized

Summary Talked about Power –P=IV Talked about Energy Gave a real world example of Power/Energy –ZeroTracer Why low power is important ATMega328P Demo Low Power communication methodologies –Send when you can, etc Xbee Demo

Questions/Comments?

References [1] - [2] - al.pdf al.pdf [3] - [4] - data/pdf2/ACA4000/ACA4000CE240.pdfhttp://industrial.panasonic.com/www- data/pdf2/ACA4000/ACA4000CE240.pdf [5] - [6] - ATmega48A-48PA-88A-88PA-168A-168PA P_datasheet.pdfhttp:// ATmega48A-48PA-88A-88PA-168A-168PA P_datasheet.pdf