Topics from meeting (October 25th)
Attendees: Jason Holmes, Scott Stack, Kin Chin Chua, Chris Romanoff
Created a list of all things that need to be interfaced with the processor and what kind of interface each one needs:
Interfaces Needed For Processor
- 1)Motor Control - 4 total PWM channels for right motor and left motor plus 2 additional ones to control the turret rotation and barrel pitch. Whether or not a PWM is 100% necessary will need to be discussed with Hong Kong.
- 2)Wireless Module – 1 SPI/UART/I2C interface to send data and configure the wireless module which will in turn send the data over the internet. The chosen tranceiver can handle all of those interfaces - the one chosen will be based on the required throughput.
- 3)Camera choices:
- a)Wireless IP camera – (nothing required for processor)
- b)Integrated camera – 9 General purpose IO and one I2C interface. Most CMOS cameras have 8 bit parallel output for image data and can be intialized and configured through an I2C interface. So, the board needs 8 general purpose for parallel data input and one for data clock. I2C interface to configure camera.
- 4)Accelerometer – 3 A/D input (1 for each axis)
- 5)IR Proximity Sensors – max of 4 A/D converter inputs (one for each sensor)
- 6)Pushbutton to detect collision – max of 4 general purpose IO (one for each button)
- 7)Fire Cannon (optional) – 1 general purpose IO (output a digital 1, which may need driving to fire)
- 8)GPS – (optional) – 2 General purpose IO pins for UART.
Sensors
- IR Proximity Sensors: The IR sensors selected have a range of 8" to 60" which is appropriate for the speed at which the tank will be moving. These will be used to detect the presence of an edge (such as the edge of a table, a stairway, or a cliff) by being positioned towared the ground. Essentially when the voltage drops it will indicate that the ground is no longer present at that point. They will also be used to detect any object in front or behind the tank.
- Pushbuttons: The pushbuttons will be added to all four sides of the tank to detect object collision. They will work in conjunction with the IR sensors, which fail to detect an object closer than 8". Bumpers will be constructed in a fashion that any contact on the entire side will trigger the button. Both the IR sensors and pushbuttons will be used trigger an action in the tank control that will override the control from the host site.
- Accelerometer: The accelerometer will be used to detect potentially hazardous angles that the tank may find itself in, such as on a hill or mound. This will trigger an action either in the tank control or by alerting the control site that the tank may flip.
Wireless Transceiver
Our choice of camera will impact what kind of bandwidth our wireless transceiver will need to handle . We determined that most image sensor cameras output too much data to be sent usefully over the internet (wireless transceiver can handle a max of 1 Mbit per second UART, but also has a 44MHz clock and SPI - so any reasonable data rate could be handled. A 640x480 color image from one of the cameras we looked at will produce about 16Mbits per second at 30 frames per second.) . We tried to figure out a way to either interface an IP camera to our website or reduce the amount of data coming from a camera. This will have to be done using MJPEG compression. The QVGA resolution of 320x240 with 15fps could potentially be transmitted without compression.
The data sheet for timing is locked to users on the manufacturer's website, but is in the process of being acquired.
