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Extending your Mark III
Mark III was designed to be a general purpose robotics platform. In particular, it was designed for expandability to provide an experimentation platform appealing not only to the beginner but also to the advanced robot hobbyist. The abilities of the Mark III can be enhanced almost without bounds, using either the options made available by PARTS or by adding your own extensions.Prototype Board
The Prototype mezzanine board is a must if you plan to interface your own circuits to the Mark III. The Prototype board is just a blank board, containing only the necessary stacking connectors to interface with the main Controller board. The Prototype board has pads and holes for mounting a variety of components. All header signals are brought out to pads for easy interfacing. Power and ground busses are provides, as well as two general-use busses. Pads are designed to accommodate .3" wide DIP chips as well as .6" wide DIP chips.Parts List
Before you begin, remove all the parts from the bag they came in and match them up against the following parts list.
| Designator | Description |
|---|---|
| J1 | 40 pin 100mil pitch dual-row stacking header .435 board separation |
| J2 | 6 pin 100 mil pitch dual-row stacking header .435 board separation |
Schematic and PCB Layout
Assembly instructions
The Prototype Board is simple to assemble. There are only two components. The only thing you need to take care with is to make sure the components are inserted on the proper side of the board.The Prototype Board is meant to stack on top of the Controller Board. Because of this, the two stacking headers that come with the Prototype Board need to have their female ends facing down, so as to mate with the male pins on the Controller Board. Identify the top of the Prototype Board by looking at the silkscreen - the top is labeled "TOP". Insert the male ends of the two header through the bottom of the Prototype Board, so that the male pins point up through the board.
When soldering the headers in place, first tack one pin on each end down with a little bit of solder. Then check to see that the header is seated firmly and flush with the board. Don't complete the soldering until you have it positioned correctly.
Since another mezzanine board may be stacked on top of the Prototype Board, you need to be sure that the solder fillets on the header pins are small. Solder has a tendancy to wick up on the pins - if too much solder is used, then it will make the pins thicker and prevent another board from being mounted on top. If you get too much solder on the pins, you can easily remove it with some soder wick, but it's easier to avoid that problem to begin with.
Sensor Board
The Sensor mezzanine board serves both as an example of how to interface a variety of sensors to the Mark III, and as a useful collection of sensors in its own right. The Sensor Board may optionally be populated with four h-bridge motor drivers, a two-axis accelerometer, and 8 channels of 12-bit A/D. Four additional pads provide space for connecting a pyroelectric detector, or alternatively, they be used as a connection point for any device that requires power, ground, and one analog or digital I/O line. Multiple sensor boards may be stacked on to the Mark III to get more A/D channels or more digital I/O or more motor drivers.Parts List
Before you begin assembling the Sensor Board, remove all the parts from the bag they came in and match them up against the following parts list. It is especially useful to match up the resistors to this list using the color code, then tape those resistors in place on the printed parts list for future use. Don't try this with the integrated circuits,
| Designator | Marking | Description |
|---|---|---|
| J1 | 40 pin 100mil pitch dual-row stacking header .435 board separation | |
| J2 | 6 pin 100 mil pitch dual-row stacking header .435 board separation | |
| J3 | 100 mil header | |
| J4 | 100 mil header | |
| J9 | 8 Pin Header | |
| J10 | 8x2 Pin Header | |
| J11 | White | 5-pin 100 mil I²C Connector |
| RP1 | 10X1473 | 9-element common-terminal 47K Ohm resistor network |
| RP2 | 8X1223 | 7-element common-terminal 22K Ohm resistor network |
| SW1 | Red | DIP Switch 6-position |
| U4 | Piezo Buzzer | |
| U6 | PCF8574 | Remote 8-bit I/O Expander for I²C Bus |
Schematic and PCB Layout
Partial Stuffing
The Sensor Board is designed so that it may be partially populated, with only the sensors that you want. The Sensor Board Kit comes with only the components needed for basic operation: the connectors, pull-up resistors, I²C interface, and piezo buzzer. All other components are optional and may be left out. Instructions for adding these additional components are included in the next section.Assembly instructions
If you have successfully assembled the Controller board, the Sensor Board should be no problem.Start the assembly by soldering the PCF8574 into the position marked U6 on the silkscreen. Then solder in the 6-position DIP switch. Although the switch is not polarized, it is convenient to solder it so that pin 1 (marked oc) lines up with pin 1 on the board (the square pad). The writing on the switch should then have the same orientation as the writing on the silkscreen.
The next components to add are the resistor packs. There are two of these, an 8-pin package which mounts next to the DIP swith in the location marked RP2, and a 10-pin package which mounds near the front of the board in the location marked RP1. The resistor packs are polarized - they need to be mounted in a specific orientation. Identify pin 1 on the resistor pack and pin 1 on the silkscreen by consulting the Appendix.
Piezo buzzer, U4. Mount in either orientation.
Connectors J9 and J10 (Handyboard Port).
Three-pin servo connectors, J3 and J4. These are mounted at the ends of the 40-pin connector, and provide two additional PWM servo connections.
The Sensor Board is meant to stack on top of the Controller Board or Prototype Board. The order of stacking, i.e. which one is on top, is irrelevant. Because of this, the 6-pin and 40-pin stacking headers that come with the Sensor Board need to have their female ends facing down, so as to mate with the male pins on the Controller Board. Identify the top of the Sensor Board by looking at the silkscreen - the top has outlines of all the chips and other components, and had most of the part designators. The bottom has very little on the silkscreen. Insert the male ends of the two header through the bottom of the Sensor Board, so that the male pins point up through the board.
When soldering the headers in place, first tack one pin on each end down with a little bit of solder. Then check to see that the header is seated firmly and flush with the board. Don't complete the soldering until you have it positioned correctly.
Since another mezzanine board may be stacked on top of the Sensor Board, you need to be sure that the solder fillets on the header pins are small. Solder has a tendancy to wick up on the pins - if too much solder is used, then it will make the pins thicker and prevent another board from being mounted on top. If you get too much solder on the pins, you can easily remove it with some soder wick, but it's easier to avoid that problem to begin with.
The last component to add is the white, 5-pin I²C connector. This is orented so that the tall white back faces the middle of the board. In this orientation the bottom of the connector should match up perfectly with the silkscreen outline and the connector should be entirely on the PCB board. If the connector is hanging off the end, you probably have it backward.
If you purchased the optional Analog Input Expander Kit, there are four additional components to add.
If you purchased the optional Accelerometer Kit, there are seven additional components to add. The Accelerometer solders directly to the 8 surface mount pads on the top side of the board. Pin 1 on the accelerometer chip is marked with a little triangle with a square around it (the Analog Devices logo) Looking at the top of the chip, orient the chip so that the text is right-side up - pin 1 will be in the lower left on bottom edge. On the PCB, the silkscreen mark for pin 1 doesn't show up. Pin 1 is the surface-mount pad on the top of the board that is connected to the through-hole with the square pad.
It's not hard to solder the Accelerometer directly to the board, but it is a pain working with that small package. Put some solder on the pads, and some solder in the connection points of the chip (the gold-colored grooves on the bottom. Put some liquid or paste flux on the pads. Position the chip over the pads and heat up the excess solder you just put on. Do one pin first and make sure you position the chip properly, then it will stay in place when you do the other pins.
The trimpot is mounted in location R7 - it only fits in in one directions. This variable resistor is used to modify the pulse frequency of the accelerometer output.
If you purchased the optional H-Bridge Kit, there are seventeen additional components to add. The four green LEDs are mounted along the front edge of the board, the four red LEDs are mounted behind them. The four 1K current limiting resistors are vertically mounted - bend one lead of each resistor so that it doubles back and lies parallel and next to the other lead. Then insert the resistor into its pads making sure the resistor body is vertical.
The H-Bridge Kit allows you to drive four DC motors, each of which interfaces to the Sensor Board via a 3-pin header. Two 6-pin headers are provided in the H-Bridge Kit in place of four 3-pin headers - this provides a more rugged connection point. Solder one 6-pin header into the spaces marked J7 and J8 on the board, solder the other into the spaces marked J5 and J6 on the board.
Stacking of multiple boards
The Sensor Board is desinged so that multiple Sensor Boards may be stacked on top of each other. If you do this, be sure to set a different I²C address for each Sensor Board, using the 6-position DIP switch.Running Sensor Board as standalone
The Sensor Board is designed so that it may be operated as a standalone board. All that needs to be done is to supply power to the board - the board's functionality may be used accessed either directly from the I²C connector or from the 40 pin header. A fully stuffed Sensor Board requires about 50mA at 5VDC, supplied either through the I²C connector or through the power pins on the 40-pin header.OOPic
The OOPic chip has its own development environment, object-oriented programming language which makes it easy to get started. Variety of third-party expansion hardware which is compatible with the OOPic as well as the Mark III. etc.- Compatibility and what is needed
- Using OOPic-compatible peripherals
Handyboard Port
The Handyboard is a popular robotics controller. Lots of information on the Internet, even some books, describe the Handyboard and how to create sensors and other extensions for the Handyboard. The optional Sensor expansion board for the Mark III has a Handyboard-compatible Digital Input/Ouput port, allowing much of this information to be used directly.- URLs for Handyboard http://www.handyboard.com/techdocs/
- Books
- Links to interfacing sensors to Handyboard
Chassis mods
The Mark III kit comes with a bulldozer-like scoop on the front which serves to support the front end of the robot as well as push opponents in a MiniSumo contest. The scoop is designed to be removable, and replaceable with a variety of other things to make the Mark III suited for other tasks. For example, in Line Following, you might want to replace the scoop with a caster to enhance maneuverability and prevent the sharp scoop edge from catching on the rough surface of the line following course.- Replacing scoop with caster
LEGO Chassis
LEGO and robotics have a long history together. Most recently, LEGO Mindstorms Robotic Invention System. To facilitate using LEGOs, the Mark III chassis was designed so that the mounting holes match the separation of holes in LEGO. You may use screws to fasten a LEGO beam to the front of the chassis, in place of the scoop, and attach LEGO parts to this beam. The standoff separation is also matched to LEGO, and the mounting holes in the Controller board are the same diameter as LEGO holes, allowing you to mount the Controller board directly onto an entirely LEGO robot chassis.Using DC Motors
Can't drive DC motors directly from PIC because of current draw. H-Bridge. Available on Sensor board. Any combination of four motors, either PCM (Servos) or PWM (DC Motors).Adding sensors
Need to provide sensors with power and external circuitry, need to read values of sensors or set value of actuators. Mark III has a variety of interfaces that make this easy.- I²C (I²C mating connector)
- SPI
- Serial
- Bit-bang
- CMUCam
- Devantech compass
- Devantech Ultrasonic ranger
- Bump sensors
- Shaft encoders
- LCD
