Difference between revisions of "S18: M.E.O.W"

Latest revision as of 03:33, 27 May 2018

Microcontroller Energy Observation Widget (M.E.O.W)

Abstract

Our project aims to provide a theft detection service by recording a video when any movement is detected in an immediate vicinity. A video feed is stored on the device to collect later on. The video feed can be used as evidence to provide authority to find the culprit. This report details the system and technology used to implement this project.

Objectives & Introduction

Show list of your objectives. This section includes the high level details of your project. You can write about the various sensors or peripherals you used to get your project completed.

Our primary goal for this project was to learn about the sleep modes that the LPC Microcontoller is capable of. In order to help us understand the functionality of the technology, we wanted to implement the sleep modes on a real life practical example.

Living in the Bay Area, a highly technological society, most tech employees travel with expensive equipment in their cars. Knowing this thieves consider this a prime area to conduct car robberies. Recently there has been an increase in these car robberies, where it can be hard to catch the criminals who have committed the theft. Often times the robbers work so quickly and discretely that a normal bystander might not consider the act suspicious. Additionally if your car is parked in remote area, far away from city cameras, it can be hard gather any evidence to catch the thief. Video surveillance evidence is highly valuable to an investigator assigned on the case.

Our video surveillance device, records footage if a crime is committed in a customers' car. Sensors in our device activate a camera to start recording when movement is detected. In its idle state, the device is in sleep mode where minimal tasks are being run on the device, which means it saves on a lot of power consumption. Alternatively if the device is constantly polling, this would use up an enormous amount of battery power. Since this device is meant to be running in a car that is not running, it is pertinent to use minimal power unless absolutely necessary to maximize the battery life.

This application can be scaled for any environment; your home, backyard, or even for city use. We can connect it every street lamp with some IOT capabilities resulting in lower crime rate across the city.

Objectives:

• Research Power consumption capabilities of micro-controllers.
• Build and implement a video surveillance device to feature the low power methods.

Team Members & Responsibilities

• R "Meow Meow" Nikfar
  • Team Lead, PCB Design, Sensor Design and Implementation, Hardware Testing, Power Analysis, Sleep-Mode Firmware
• Ahsan "Whiskers" Uddin
  • BeagleBone Testing, Video Capture Implementation, Storage, Sleep-Mode Research
• Nelson "Fluffy" Wong
  • Deep Power Modes, Power Analysis, Communications
• Britto "Kitty Kat" Thomas
  • CAN BUS Low Power Research, Power Analysis, System Design
• Sai Kiran "Mittens" Rachamadugu
  • Testing, Board Communications, User Interface

Schedule

Parts List & Cost

• BeagleBone Black Wireless $55
• Logitech HD PRO WEBCAM C920 $70
• 3 PIR sensors $45
• 1 SJ One board $80

Design & Implementation

Hardware Design

GPIO Pins

M.E.O.W uses three PIR sensors , each of these sensors are connected to GPIO pins on port 2.3 , 2.4 and 2.5. Any motion detected asserts these pins creating a WIC to wake up the system from sleep.

GPIO pin 1.28 is asserted to signal beagle bone to start recording.

Low-Level Hardware

The low-level design starts from the PIR Motion Sensors and ends with the storage of the video data. The LPC1758 plays a big role in the communication of the overall system. The PIR sensors are each connected to the LPC1758 using a GPIO protocol and send signals if an object or and person is within their range. Once the signal is sent from the Sensors, the LPC wakes up and consumes power from the PCB which either uses the power from a plugged source or the backup LIPO battery. LPC then sends the right information to the BeagleBone board using UART protocol.

Software Design

freeRTOS Tasks

For this project, we use two RTOS tasks, one for asserting GPIO pin needed for beagle bone and the other to put the LPC board to sleep. The PIR task which asserts GPIO pin is given a higher priority compared to the task which puts the LPC board to sleep.

Psuedo-code

Void PIRTask (void* pvParams){ 
              while(1){
                 if(xSemaphoreTake(xGetSemfromISR,portMAX_DELAY){
                 
                       // assert GPIO pin to signal beagle bone for recording video
                       LPC_GPIO1->FIOSET = 1 << “pin number”;
                }
        }
 }

Above code allows PIRTask to assert a GPIO pin to signal beagle bone to start recording. To put the LPC board to sleep a second task with lower priority is run. This task in-turn calls appropriate sleep mode.

Void PutToSleep(void* pvParams){
	While(1){
             if(xSemaphoreTake(xGetSemforSleep,portMax_DELAY){
                      //call appropriate sleep function
                       enter_powerdown();
 
             }
        }
  }

Interrupt request handler is created for above tasks which uses xSemaphoreGiveFromISR on interrupt to give a semaphore to the tasks. The code given below shows a pseudo-code for the Interrupt handler.

  void Simple_IRQHandler(){
         
        long yieldRequired = 0;
        xSemaphoreGiveFromISR(xGetSemfromISR, &yieldRequired);
        portYIELD_FROM_ISR(yieldRequired);
  
   }

Printed Circuit Board Design

In order to stabilize and provide a noise free power supply to all the components of the system, a printed circuit board(PCB) was created. This piece of hardware brings all the power consumption of the unit together. The design and the creation of the board was done in Eagle Schematics Software where the gerber files were created. Once the gerber files were ready, the files were sent to be printed. There were 2 iteratins of this board. The first lacked the necessary connections for the additional components and had several noise reduction flaws. The second board solved all these issues. Note that the final board had to be 1 layer due to the noise reduction characteristics of the material and the ability for placement of the LIPO battery on the bottom of the board.

NXP LPC1700 Series Power Modes

Power management functionality in LPC 176x CPU

There are mainly 4 modes of runtime power savings mode that are available in LPC 176x CPU. They are described in details as follows. Measurements were made using an Agilent Infiniium MSO9254A, a N2870A passive probe, and a 1147B current probe. It should be noted that our SJ One board generally runs at 96MHz with 5V input voltage and consumes about 177mA of current which corresponds to 885mW of power.

Deep sleep

Upon entering the Deep sleep mode, the main oscillator is powered down and the DSFLAG in PCON is turned on. We observed that the current consumed at this state was 167mA which corresponds to 835mW of power. To wake up from Deep Sleep, an EINT0 was used to resume the CPU. Note that as PLLs are shut off during this sleep, the PLLs are configured once the CPU is resumed from deep sleep.

Power Down mode

Upon entering the Power Down mode, like deep sleep the main oscillator is powered down but additionally the flash is also turned off. We observed that the current consumed at this state was 80mA which corresponds to 400mW of power. To wake up from Deep Sleep, an EINT0 was used to resume the CPU. Note that as PLLs are shut off during this sleep, the PLLs are configured once the CPU is resumed from deep sleep.

As we learnt in this semester that frequency plays a role in power consumption, and as we know that the default frequency of the LPC board is 96MHz, we tried the same power down sequence wit 8MHz. This time we saw that the current consumption went down to 24mA which corresponds to only 120mA!!! By far, this was the most stable power saving feature we have tested and we implemented this setting in our project.

Deep Power mode

Upon entering the deep power down mode, the entire chip is powered down except the RTC and the DPDFLAG in PCON is turned on. We observed that the current consumed at this state was 60mA which corresponds to 300mW of power. To wake up from Deep Sleep, there is only one way i.e to set the RESET pin, which replicates very closely to the cold boot process.

Summary of Power modes

Below is a chart for all the power savings comparisons side by side.

One things that needs to be noted is that although we are manipulating the power states we are still seeing a significant amount of current being drawn constantly. For example we are claiming that in deep power down, the ASIC is switched off but yet we see 60mA of current being drawn. The answer is that is even though the ASIC is switched off, there are other peripherals that are still ON. For example the 7 segment LED. So ideally it would be interesting to see what happens when each and every single peripheral is turned off dynamically in each state and to see the absolute power savings consumption.

Entering

Power mode entry is based on tables 44 (Power Mode Control register) and 662 (SCR bit assignments) of UM10360 [1].

Please note the following, regarding the interaction between power modes and debugging status. If P2.10/EINT0/NMI is asserted voltage-low, the LPC will boot in debug mode. In debug mode, the LPC will not wake in the same manner. Since we do not program the LPC via JTAG/SWD, this is not a problem for us.

void enter_sleep()
{
   LPC_SC->PCON = 0x0; // Table 44
   SCB->SCR     = 0x0; // Table 662
   __WFI();
}

void enter_deep_sleep()
{
    LPC_SC->PCON  = 0x8; // Table 44
    SCB->SCR     |= 0x4; // Table 662
    __WFI();
}

void enter_powerdown()
{
    LPC_SC->PCON  = 0x1; // Table 44
    SCB->SCR     |= 0x4; // Table 662
    __WFI();
}

void enter_deep_powerdown()
{
    LPC_SC->PCON  = 0x3; // Table 44
    SCB->SCR     |= 0x4; // Table 662
    __WFI();
}

Note the use of of __WFI(), which the compiler resolves as the assembly directive

__ASM ("wfi");

Exiting

On exiting a power mode, the associated bit on the Power Mode Control register must be cleared. As noted in the datasheet, bits 8, 9, 10, and 11 are associated to the particular power modes, and these flags are cleared in software by writing "one" to the associated bit.

void clear_sleep()          { LPC_SC->PCON |= 1 <<  8; };
void clear_deep_sleep()     { LPC_SC->PCON |= 1 <<  9; };
void clear_powerdown()      { LPC_SC->PCON |= 1 << 10; };
void clear_deep_powerdown() { LPC_SC->PCON |= 1 << 11; };

The PLLs (phase-locked loops) are turned off upon entering deep sleep, power-down, and deep power-down. Additionally, the IRC (the 4 MHz internal reference clock) and the clock dividers are reset when entering power-down and deep power-down. Therefore, the system clocks must be reconfigured/reinitialized when exiting any of these power modes.

We can take advantage of sys_clock_configure() from L0_LowLevel/sys_clock.cpp to perform this initialization.

One more thing to keep in mind regarding power mode exits: when exiting deep sleep, power-down, and deep power-down, there is a non-zero amount of time that must elapse before the system is able to resume processing. In all three cases, a timer starts counting the moment the power mode is exited, and code execution can resume after this timer expires.

• If the IRC was used prior to entering the power mode, then the 2-bit IRC timer is used, and it lasts is 2² = 4 cycles long.
• If the main external oscillator was used, then the 12-bit main oscillator timer is used, and it lasts 2¹² = 4096 cycles long.

Moreover, in power-down and deep power-down, the flash undergoes wake-up, and its wake-up timer must expire (approximately 100 µs) before it can be used. This means that no instructions can be fetched from flash for execution until this timer expires.

Features Summary

Below is a tabulation of the features that are enabled or disabled for each power mode.

Testing & Technical Challenges

Testing

• Power Consumption Testing
  • A big part of our project was to understand the power consumption of the LPC board under the different sleep modes, The results of that test are provided above.
• PIR Sensor Behavior
  • We tested the sensor to understand the kinds of signals it produces in the LPC. There are a couple of settings on the sensor that needed to be calibrated to fit our needs.
• Camera Recording
  • Since the Beagle bone worked off a trigger to start recording, we tested that subsystem to function well under several circumstances, like a constant high trigger, frequently fluctuating trigger as well edge cases.

Technical Challenges

• Stable PIR signal
  • We had trouble putting the LPC to sleep since the PIR Sensors kept outputing signals even when inactive (Noise). So we had to develop logic to create a min/max values for a specific period of time to trigger the deactivation of sleep.
• 3D print quality
  • We had to create multiple iterations to make the housing Fit our devices. We still need to make more exact measurements to fit our components.
• Contradictions in documentation
  • We read through several pieces of documentation to understand the differences between the sleep modes until we came across the exact publication for the LPC module sleep modes. Same goes for the PIR sensors.

Conclusion

This project really helped us understand the capability of the sleep modes on the LPC system. It can definitely be used in several applications to save battery life. It is very simple to implement if you read through the data sheet completely. We would have also liked to implement the sleep mode in the Beagle bone to get a true power reading but didnt want to invest too much time in learning the beagle bone, but rather learn the LPC sleep modes as a proof of concept.

Project Video

Project Demonstration

Project Source Code

All the power management driver code has been referenced above already. Moreover for BeagleBone video drives, the following open source code was used

V4L2 API Video driver for Linux

References

Acknowledgement

Thanks to Preet for always encouraging us to do great things and last but not the least, to let us use the name "MEOW" for our project.

References Used

List any references used in project.

[1] NXP Semiconductors. (19 Dec. 2016). UM10360: LPC176x/5x user manual.

[2] NXP Semiconductors. (25 Feb. 2010). AN10915: Using the LPC1700 power modes.