National Engineers Month

	Activities by Grade	K - 2		5 - 8
		3 - 4		9 - 12

CD-ROM Drive

__________ Before you take anything apart

• What voltage(s) are required for this device? ______________________
• Are there any warning labels? ________
• Are there any indicator lights? ________
• Are there any pushbuttons or other switches? ________
• What kinds of tools are needed to get inside the case? ____________________

__________ Open the case – Use the correct type of screwdriver

• Remove enough of the case to reveal the mechanisms and circuit boards.
• How many motors can you see? ________
• How many circuit boards are there? ________
• Find the indicator lights and switches that you saw outside
• Are they attached to a circuit board? ________
• Can you manipulate the switches from inside the case? ________
• Use the battery pack to try to light the indicator, which is usually a light emitting diode (LED). Does it light if you reverse the connections? ________

__________ Examine the circuit board(s)

• How many large integrated circuit (IC) chips are there? ________
• What do they do? Beats me.
• Find the one with the most package pins. This chip may be a microprocessor or microcontroller, or maybe not. The largest chips could be controllers for the motors, controllers for communication with the rest of the computer, or memories for buffering data while it is being read from the CD-ROM.
• Was there any plastic or other insulation on the inside of the case to prevent the circuits from touching the case? ________
• Locate where the wires or cables from the motors connect to the circuit boards.
• Is there a beefy-looking chip near this location? ________
• If so, it may be the driver that supplies the high electrical current for the motor. Such chips may get hot enough to require a "heat sink" to channel excess heat away from the transistors inside.
• Is there any metal attached to this chip? _______
• If so, it is probably a heat sink. Is insulation absent from the case at this location to allow heat from the chip to flow into the metal of the case? ________

__________ Check out the mechanisms

• Find the laser head that reads data from the CD-ROM.
• Can you move the motor or gears that slide the laser head back and forth? ________
• Does your CD-ROM drive have a tray for inserting the CD-ROM, or does it just have a slot instead? ________
• If there is a tray, can you move the motor or gears with your fingers to drive the tray in and out? ________
• If there is a slot, this is an old style CD-ROM drive that required the CD-ROM to be in a special cartridge that was inserted into the slot. Can you move the motor or gears that operate the cartridge manipulation mechanism? ________
• Can you rotate the motor and spindle that spin the CD-ROM? ________

__________ Run the laser head and disc manipulation motors

• How many wires are connected to the laser head motor? ________
• How many wires are connected to the disc manipulation motor? ________
• If there are two wires:
• Connect one power supply clip to one of the motor terminals and touch the other power supply clip to the other terminal on a motor. If you cannot reach the motor terminals with the power supply clips, try using a paper clip to make a narrower extension and probe with that. What happens? __________________________
• Reverse the connections. Now what happens? __________________________
• Repeat with the other motor.

__________ Run the disc spindle motor

• How many wires are in the cable connected to the disc spindle motor? ________
• Unplug the cable from the circuit board.

__________ Look for sensors

• Often a motor driven mechanism will contact a switch (called a limit switch) at the ends of its range of travel, and this will either directly cut off the electrical supply to the motor or else signal the motor controller to stop the motor. This may be a mechanical, optical, or magnetic sensor.
• There are probably no magnetic sensors here.
• Are there any mechanical switches that the laser head mechanism or the disc manipulation mechanism will touch? ________
• An optical sensor consists of an LED beaming its light to a receiver, where the beam can be interrupted by part of the moving mechanism. The LED and receiver may either be separate, or else built into a package together with a slot where the beam can be interrupted. Are there any optical sensors? ________
• If there is no physical sensor, how do you suppose the motors know when to stop (e.g., how do they know when the laser head is positioned at the beginning of the disc, or when the disc tray is all the way in)? _____________________________________ _____________________________________________________________________ _____________________________________________________________________

Questions for further consideration

• What things were done to simplify assembly?
• Could it be simplified even more?
• What things were done to make the CD-ROM drive compact?
• Could it be made even smaller?

Take it all apart

• The drive belongs to your group. Remove the motors. Take apart whatever you like. Put parts in the bag. Separate metal parts for recycling.
• If you want to take anything home, your group must decide fairly who gets what. Intel coordinators will mediate, if necessary.