Tuesday, January 19, 2010



Design MSP430 Ultra-Low Power Challenge
Link to the Contest Entry


Introduction
Cooking has been the one of the most important tasks since the dawn of human history. The progress in this field has been very significant both in terms of techniques and the means. The initial means was the use of Fire and still is the most preferred source utilized for cooking.
The fuels used in this type of technique are generally of the Conventional type – wood, compost, bio-gas and the most popular Liquid Petroleum Gas (LPG). Even though there have been several other technologies like Microwave, Induction Cooking and Ovens, LPG based cooking constitutes 60% of the worlds cooking fuels. The fuel LPG is a natural resource and has limit to its availability. Thus saving this fuel becomes a mandate in the present world context of diminishing resources.

Objectives
This project CookHa intends to solve the problem of monitoring the use of Liquid Petroleum Gas without directly taping into the Gas Cylinder and complex installation procedures.
The following are the objectives laid out to be fulfilled by this design:

Usage Controlling:
The device CookHa intends to control the usage of the Liquid Petroleum Gas (LPG) by monitoring the time of cooking. This is done using the Temperature Sensor located near to the stove to sense temperature changes while the cooking is in progress. In case of excess usage beyond the programmed usage a warning is shown.
[There can be several programmed Usage Patterns for cooking but for ease we would restrain ourselves to only one pattern. Also the Dynamic calibration for these Usage Patterns is not provided yet but would be a valuable addition.]

Low Power Consumption: This device CookHa would be optimized for power consumption so that the battery life can be very long.

Design
The above defined objectives would be delivered using the TI® MSP430F2013 microcontroller. This microcontroller would used at the <3.3V operating voltage and would be assisted by a CR2032 Battery source. The oscillator for the Main CPU clock MCLK would be from the Internal DCO oscillator at 1MHz and the Timer as well as the ADC would run off the VLOCLK by the ACLK channel. This would use a sealed metal Temperature Sensor for high temperature sensing and exposure. The two LEDs used in the system would serve as status indicators (RED – Temperature Scan | GREEN – Program Execute). The button press is used to activate the system or to exit the error condition. The second button is kept for future use as calibration button to make the Usage Patterns programmable.

Schematics:










The temperature sensor is powered by an MSP430 pin so that when not required it can be switched off. LEDs being Active Low can easily be switched off by giving a High on the pins. The Push button uses a internal pull-up with as Interrupt-on-Change feature. For the ADC we use the 1.2V internal reference that can be turned ON when the sampling is needed and then turned off when not required.
To further reduce the power consumption from the ADC the Channel is deselected and the pins are returned to normal state.

The Figure Shows the Flow Chart for the Software:


Power Calculation
The estimate for the Different Modes can be added up to the Final Power Consumption.
1. Scanning Mode:
    LED power consumption     = 800uA
    ADC Consumption          = 200uA
    MSP430 Core Consumption      = 300uA
    Hence, Total Consumption    = 1300uA
     Frequency of this Consumption = 5000mS/(24*60*60*1000)  [ Every 5 Seconds ]
     Total Time Spent in Processing = 100mS
     Sleep Current (LPM3)        =  0.9uA
     Total Sleep Time = 5000 – 100 = 4900mS
     Now, Total Scanning Mode Power = 1300uA * 100mS + 0.9uA * 4900mS = 134.41mAmS
     Average Current = 134.41/5000 = 0.026882mA
2. Cooking Mode:
    LED power consumption     = 800uA
    MSP430 Consumption        = 300uA
    Hence Total Consumption     = 1100uA
    Frequency of this Consumption = 1000mS/(24*60*60*1000) [ Every 1 Seconds ]
    Total Time spent in Processing  = 10mS
    Sleep Current (LPM3)                 = 0.9uA
    Total Sleep Time = 1000 – 10 = 990mS
    Now, Total Cooking More Power = 1100uA * 10mS + 0.9uA * 990mS = 11.891mAmS
    Average Current = 11.891/1000 = 0.011891mA + 0.026882mA [ Since the Scanning is also ON]
    Hence Total Average Current = 0.038773mA
3. Alert Mode:
    LED power consumption    = 800uA
    Since the MSP430 is completely in sleep hence there is no power consumption from it.
    Frequency of this Consumption    = 100mS/(24*60*60*1000) [ Every 0.1 Seconds ]
    Total Time Spent in Processing     = 10mS
    Sleep Current (LPM3)        = 0.9uA
    Total Sleep Time = 100 – 10 = 90mS
    Now, Total Alert Mode Power = 800uA * 10mS + 0.9uA * 90mS = 8.081mAmS
    Average Current = 8.081 / 100 = 0.08081mA
4. Normal Mode:
    Since in Normal Mode it has nothing switched ON so the only consumption is that of MSP430
    Average Current = 0.0001mA

Total Average Current of All modes = 0.146565mA = 146.565uA
Now Checking for CR2032 Capacity:
Total Capacity = 225mAh
Asuming 60% Usability and Expressing in mAmS form -
Total Usable Capacity for CR2032 = 11664000000.000mAmS
Hence, Total Battery Life = 22106.23Hrs = 921 Days = 2years 6 Months
(The Calculation is for the worst case current consumption and would also vary as per usage)

Future Scope
I have presently considered only a specific temperature profile and time for the cooking. We have only one program for a particular cooking pattern. This can be extended to multiple programs. Another feature would be the calibration feature using which multiple temperature profiles and cooking patters can be recorded as custom programs.

Picture of the Device

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