March 4, 2011
CPE 322 Camera Level Indicator – HW5
Thomas Dabay, Kris Engel, David Quirk
3/4/2011
I pledge my honor that I have abided by the Stevens Honor System
The Group
The group will consist of three members. David Quirk will be the group leader and is currently a 4 out of 5 CPE major. For this particular report, David’s responsibilities will be to provide information on hot shoe technology, more specifically the power requirements.
Kris Engel is a 4 out of 5 CPE major and will focus on the microcontroller programming portion of the project.For this particular report, Kris will be researching about the Arduino microcontroller, a board that is used in many products and by hobbyists alike.
Thomas Dabay is a 4 out of 5 EE major and will focus on any electrical aspects of the project including the wiring of fiber optics and any circuitry associated with the microcontroller. For this particular report, Thomas will be providing research on a gyroscope sensor; particularly one with a single axis monitoring system
Preface
The group has come closer to picking particular types of items to be used in the project. The group has decided on a type of Arduino processor and a gyroscope that only monitors one axis of rotation. The gyroscope will only monitor the camera’s level in terms of the y plane.
Microprocessors
What is a microprocessor? By now, most know what it is, but the group will provide a small description. A normal computer consists of a central processing unit, memory and I/O or input and output. The CPU takes care of the logic and mathematic functions. The memory is where data is stored. The I/O dictates how the computer moves data between components and outputs it to, say, a screen. A microcontroller takes all three of these things and packs them into one single component. Because of this size, some of these processes are limited in their complexity. A regular desktop computer can perform thousands of tasks, but a microcontroller excels only at one. In the case of this project, limiting the output to LED lights being on or off is simple enough to merit the use of a microcontroller.[1]
The microprocessor will have several responsibilities. First, it must be able to interface with the power output of the hot shoe port on the camera. Second it must have enough outputs to support 3 LEDs. Each LED will indicate whether the camera is tilted left of center, right of center or at center. The microprocessor must do all of this while consuming very little power and being small in size. This product will have to sit atop the camera, so not bulking the camera too much is a top priority. For purposes of developing a project where the code will constantly be tested and debugged, EEPROM or flash memory is a must. Other forms of memory are not ideal for this type of development.
The Arduino
After doing some research, the group found that the Arduino line of microcontrollers would work best. The sheer flexibility provided by this line of microcontrollers is appealing, and one of them surely can provide all the needs for this project. The Arduino is open-source hardware. Anyone can download the design files and make their own variations. There is a very specific size constraint for the group’s project, and two particular Andruino models, the mini or mini pro, are ones that can satisfy these constraints. These models would need an additional circuit that latches onto the mini in order to interface via a wire to a computer.
Figure 1 – FTDI Basic Breakout
Figure 2 – Arduino Pro Mini
Figure 1 shows the FTDI Basic Breakout, a small chip that goes on the pins labeled Programming Header in Figure 2. This provides the necessary interface to communicate with a computer to upload code[2]. The Arduino utilizes its own custom programming environment and is compatible with Windows, Linux and Mac. The mini pro has an ATmega168B with an operating voltage of 3.3V or 5V depending on the model. It has 14 digital I/O pins and 6 analog input pins. It has 16KB of flash memory, 1KB of SRAM and 512 bytes of EEPROM. It runs at 8MHz with the 3.3V model or 16MHz with the 5V model.
Gyroscopes – An Introduction
A gyroscope is any device that is able to measure angular velocity. The first gyroscopes were created in the 1800s, although similar devices were used for ship navigation as early as the 1700s. In 1852, Leon Foucault coined the term “gyroscope”. The 1900s saw many improvements to the gyroscope, namely with the introduction of optical gyroscopes using lasers, which found success in aeronautics and military applications, and Microelectromechanical Systems (MEMS) gyroscopes, which thanks to their small size and ability to be mass produced are popular in many applications. The commercial applications of gyroscopes, especially MEMS gyroscopes, are wide and varied and span major categories such as automotives, consumer electronics, aerospace, military, and industrial applications.
MEMS Gyroscopes
As mentioned above, the MEMS gyroscope has the advantage of small physical size and good manufacturability, which leads to lower prices for consumers. It is because of these properties that they are of especial interest to this project. They are also very accurate compared to older mechanical gyroscopes. There are various different types of MEMS gyroscope, but most make use of vibrating mechanical elements to sense rotation. As such, they lack rotating parts and bearings, which is what allows them to be miniaturized effectively. All such vibratory MEMS gyroscopes make use of Coriolis acceleration in sensing rotation. Most MEMS gyroscopes can be broken down into three quality levels. In increasing quality levels, they are rate, tactical, and inertial grade.
The first type of MEMS gyroscope is known as the tuning fork design, which originated in Charles Stark Draper Lab. The tuning fork design consists of two tines connected to a junction bar which resonate at a certain amplitude. When those tines rotate, the Coriolis effect causes there to be a force perpendicular to the tines which can be detected and are proportional to the angular rate. The force is detected by changes in the capacitance of gyroscope because the distance between the tines is affected by the force.
Another type of MEMS gyroscope is the vibrating wheel gyroscope. It consists of a wheel that is driven to vibrate about its axis of symmetry. When rotation occurs about either in-plane axis, the wheel tilts, which can be sensed with capacitive electrodes placed under the wheel. One advantage of vibrating wheel gyroscopes is their ability to sense two axes of rotation with a single vibrating wheel.
The next type of MEMS gyroscope is the Piezoelectric Plate Gyroscope. It is preferable to other types of MEMS gyroscope because of the lower drive voltage required for readable outputs. It consists of a piezoelectric plate suspended over a silicon wafer. Leads are connected to each of the 6 sides of the piezoelectric plate, and the leads provide the driving voltage and measure the output as the plate vibrates.
A final type of MEMS gyroscope is the wine glass resonator type. In this type, the resonant ring is driven to resonance and the positions of the nodal points indicate the rotation angle. Although the input and output modes are nominally degenerate, but due to imperfect machining some tuning is required.
One common drawback of a MEMS gyroscope is that most output an angular rate measurement, instead of an absolute angle measurement. This would not be a problem ideally, because one would need only integrate the angular rate measurements to get an absolute measurement. However, because of various errors in measurement (bias error, random error/noise, etc.), this method can become very inaccurate. As such, either proprietary measures are necessary or one must calibrate each individual sensor. For full manufacturing, proprietary measures are usually more economically viable, but for prototyping, testing, and small batch manufacturing, calibration is often preferable. With proper calibration, most MEMS gyroscopes are able to reach less than 1% error rates when measuring absolute angles.[3]
Useful information about the proposed gyroscope can be found in the footnote below.[4][5] It is a single axis MEMS gyroscope that was chosen for its high sensitivity, small physical size, and affordable price. It is manufactured by STMicroelectronics (part number LY503ALH, mouser.com part number 511-LY503ALH).
More Articles about Gyroscopes
This discusses new, small gyroscopes that assist in image stabilization in cameras.[6] This discusses the recent shrinking of MEMS technology size and prices.[7] This discusses future outlooks on MEMS technology.[8] This discusses MEMS testing and calibration in mass production situations.[9]
Hot Shoe Technology
The Hot Shoe is a port located on most, if not all, SLR cameras (digital and film) and a handful of upscale point-and-shoot cameras. This port is used to provide a mounting point for an external flash or flash system. The port has a multitude of contacts that connect to the Hot Shoe and provide a connection to the camera’s power and sync system. When the shutter is depressed fully, an electronic signal is sent through the contacts in an arch through the flash device which triggers the flash to discharge. Flashes use their own power supply in order to supplement the brunt of the flash power, but the voltage arc through the contacts gives the flash a jump-start and signaling point to discharge. The group’s device hopes to use this source of energy to power the device that we are using. Figure 1 shows that the Hot Shoe port has a universal specification for sizing and contact points as provided by ISO 518:2006[10]. Access to this standard would be necessary in order to continue on with the project and further the integration with the standard. There are references online indicating the pin arrangement[11] and how power is transferred through the system, but no specifics are given as to what kind of voltage passes through the contacts.
Today, though, the Hot Shoe is used as a proprietary port by camera manufactures to connect in-house flash systems. This makes the project somewhat more difficult. Coordination with specific manufactures will be necessary to learn about how power is used within their implementation of the Hot Shoe system. Access to ISO 10330:1992[12] will also be necessary to learn about the minimum requirements of ignition circuits through the Hot Shoe port. This standard will show what the minimum amount of power is that goes through the port. Using this, the group can, in turn, determine the power requirements for the unit they are developing. By coordinating with the manufactures, the group can also tap into the auxiliary contacts on the Hot Shoe to gain continual power input.
The team understands that there is a possibility that even through proprietary ports, continual power draw may be impossible. For this, there is a backup plan. When a device is connected to the Hot Shoe port, every time the shutter is engaged, a voltage is sent through the port. Using this fact, the group should be able to device a capacitor/recharging system that taps into that power. When the power is sent through the port, the device will collect the energy and store it in a capacitor. Using this constant recharging ability, the device should be able to self-sustain itself during regular usage and power the microcontroller and LED system.
For the purpose of this project, the group will lock in their research to a specific manufacture in order to simplify the project in every aspect. The company of choice is Canon. This company’s pin-out is the most symmetric and similar to the original ISO specification. The reported voltage from many independent sources[13]is 5V from the X-sync contact (the largest, circular, center contact). According to this source, it seems that the Hot Shoe supplies a constant voltage of 5V through the X-sync and drains the voltage supply during the shutter discharge and power recycle. Hopefully, this works out for the group’s device and it can draw from that 5V pin to power the circuit/microcontroller/LEDs.
The Hot Shoe port had to be tested for power output due to there being no resources available to see what kind of voltage this port develops. After multiple tries, we were able to find a contact on a Canon Hot Shoe that outputs voltage at the half button-press and continue to provide a constant voltage 5-6 seconds after release of the button. This port is the data transfer port that is driven by the flash module. The group’s guess is it provides this voltage to sync the flash module with the camera and drive it to check the conditions of the photograph to set things like ISO, shutter speed and aperture correctly. This would be extremely useful for our project seeing as the device only needs to be on when you are moments from snapping a picture. The problem with this is that the voltage is very minute: about 11.5mV (this was measured by the group manually as there are no resources available that indicate this value to us). This would not be enough to power the unit on-demand to check for a level picture. But, this voltage can be used as a trigger to activate the unit from a sleep mode. It is best for the device to remain off until it needs to be used to conserve battery life. So, the device will use this port to awake the device from a sleep state. Now, the device needs a viable power source to run the device.
Alternative Power Sources
One power source the group was interested in using is watch cell batteries. These batteries are utilized in many applications of this magnitude where a small, simple task needs to be executed by a logic board. These batteries are easy to find and replace. The only downside is that these batteries can be expensive and if you run out in a pinch in a more remote area, it can be harder to acquire these batteries than it would be to find a power outlet and recharge a unit. That’s where our second option comes in: rechargeable batteries. These would be more useful overall. If the group can find a small enough unit, (which exists, because the iPod Shuffle is probably smaller than our unit is projected to be and that lasts for 20 hours) we should be able to power the device for long enough to be a viable project. The upside to this is there is no need to replace batteries and if the device runs out of power you are only limited to the nearest power outlet or recharging unit. The downside is this may increase the bulk of the unit to accommodate for the battery itself and the external port required to provide power to the unit. There are many resources available that explain the technology available in many form factors of battery types.[14][15]
SWOT
Strengths – The product is needed in the market, no other products provide the convenience of the group’s proposed product. The product is cost effective and would be cheap enough on a production scale to sell at a reasonable price for both serious and above average camera users.
Weaknesses – For the particular camera the group is aiming to fit this device, there could be a problem trying to fit the device on top of the camera. The camera has a pop-up flash which only allows about three quarters of an inch of space to situate a microcontroller on top of. The product will need an external source of power
Opportunities – The hot shoe can provide a signal that activates the product, which will cut down on power consumption.
Threat – The camera’s ability to stabilize itself is based solely on the user’s initial calibration. If this is not done correctly, (although through no fault of the company’s) the product may not work. If the hot shoe pass through cannot be executed, other accessories cannot be used. This may also cause deteriorated flash output.
Bibliography
The E-TTL Protocol. (2007, October 3). Retrieved February 2011, from Kzar.net:
InvenSense Inc IDG-2000: Dual-axis gyroscope improves optical-image stabilization. (2009, September 11). Retrieved March 2011, from EDN Electronics Design, Strategy, News.:
Arduino Pro Mini. (n.d.). Retrieved from Arduino:
Bernstein, J. (2003, February 1). Acceleration/Vibration. Retrieved February 2011, from Sensors:
Brain, M. (n.d.). How Microcontrollers Work. Retrieved February 2011, from Howstuffworks:
Burg, A., Azeem, M., Sandheinrich, B., & Wickmann, M. (n.d.). MEMS Gyroscopes and Their Applications.
Chatterjee, P. (2010, January 7). MEMS, sensors, and nanotechnology. Retrieved March 2011, from EDN Electronics Design, Strategy, News:
Conner, M. (2009, June 9). MEMS-based motion sensors move lower in both size and price. Retrieved March 2011, from EDN Electronics Design, Strategy, News: