The board was created using the KiCad software suite. See License file for license of this board and license information and attribution for included files.
The directory gerber contains the gerber files for board layout. The zip file in the gerber directory is the files that will be sent to the PCB vendor.
The directory pdf has the board schematic (top.pdf), and the board layers.
The directory info has this file, a spreadsheet of the BeagleBoard pins used, and the board license.
The directory bom has the bill of materials for building the board.
The directory all_fp.pretty is the PCB footprints used for the board.
top.pro is the kicad project file.
Other files are various kicad files.
The directory datasheets has datasheets for the chips used.
The board is laid out such that it matches the normal drive connector locations and orientation when installed with the component side down. The BeagleBone plugs into the upper solder side of the board. The assembled height should allow installation in a half height 5.25" drive bay.
The mounting holes in the board match the standard 5.25" drive bottom mounting holes. If the drive being emulated was mounted with screws into the bottom of the drive the board can be mounted using standoffs. The board is shorter than a normal drive so the connectors will be further back.
For drives that mounted using side screws, mounting rails for the board will need to be made. Space has been left along the side of the board to allow the board to be screwed to the rails. I expect to use a strip of wood.
The J8/J9 connectors for the BeagleBone black (U1) should be installed on the back/solder size of the board with the short pins soldered to the board.
J6 is rotated opposite other components to match the orientation of J1
The capacitors C1-C5 may be installed on the side of the board that makes it fit better for the mounting method chosen.
The cables mating to J4 frequently have pin 15 plugged for polarization so you may wish to remove that pin before installing the connector.
The cables mating to J3 frequently have pin 8 plugged for polarization so you may wish to remove that pin before installing the connector.
The primary part DC/DC converter U12 is not marked clearly with which pin is 1. Verify correct orientation from the data sheet.
The DC/DC converter U12 has pads very close together. Watch out for shorts when soldering.
You may wish to build the power supply section first, test voltages, build rest, test voltages and P9 39 voltage. P9 39 voltage should be .125 * 12V input, nominally 1.5V.
The board has capacitors to provide power for a short time when power is lost to perform a clean shutdown of the operating system. This prevents corruption of the flash memory or data loss. If this is not desired don't install the following components: C1-C9, U6-U10, R8-R16, R19, D1-D3, F1, and U12. Connect P2 (5V) to the 5V side of C7. You may wish to leave C6 installed for bulk decoupling.
If the ability to read an existing disk is not desired don't install components C11, C16, J3, J4, P1, U5, U16, R5, R6 and RN3. If emulating a second drive is not desired components U15 and C15 can also not be installed. U15 and C15 are used for both reading disks and second drive emulation.
If drive emulation is not desired don't install components U2, U3, U14, RN1, RN2, R2, R3, C12, C13, and C18.
If second drive emulation is not desired don't install C14, U13, J6, R3, and R23.
If BeagleBone shield auto identification of pins used is not desired don't install U11, P4, R17, R18, and C17. R20 and R21 can also not be installed if I2C is not used on J7. Programming the EEPROM is at least as difficult as setting up a script to perform the configuration at boot so it's probably not worth installing these components.
LED D2 is used to warn that the capacitors are still charged. If this is not needed don't install D2 and R14.
If expansion signal connector is not desired don't install J7.
Parts were chosen to be available at Digikey and Mouser. If a part was available from both it was chosen otherwise an alternate part is shown in the parts list. You may be able to substitute parts with the particular distributor you are using to get lower price.
For the headers both shrouded and unshrouded headers are listed. Use the type you like. The gold plating thickness varies on the parts listed. Some are only gold flash. If thicker plating is desired to allow many unmating cycles other parts may be chosen.
For U14-U16 the 74F07 is listed as the primary part since it fully meets the output current requirement. The 7407/74LS07 should be usable though the low noise margin will be degraded. The required current is about 21 mA at .4 V low voltage. The 7407/74LS07 is specified at 16 mA at .4 V and 40 mA at .7V. The 74F07 is specified at 64 mA at .5V.
For DC/DC converter U12 the primary part requires the external capacitors C6-C9. The datasheet for the secondary part LDO03C says it does not require external capacitors though they can still be installed for better filtering. Other options would be one of the 10 uF for the input and output or just put the .1's in for C6-C9. The LDO03C appears to have a lower dropout voltage so should give slightly longer run time on the capacitors.
I have purchased many of the parts to verify the parts list is correct but not all. You may wish to check headers and alternate parts before purchasing.
For reading an existing drive connect it to J4 and J5. Jumper P1 if writing to the drive is desired. Currently the software does not support writing to a drive. See the emulation software for how to operate the software.
For emulating a drive connect the control cable to J2 and data cables to J1. To emulate two drives connect the second data cable to J6. Note that two drive emulation mode does not currently have software support. It will only work if the system shared the control cable between the two drives being emulated. See the usage information on this page.
J7 is for connecting operator controls or status displays. No software support is currently provided. Any I/O must be 3.3V to prevent damage. See board design notes for more information
For drive emulation, scripts will need to be created to automatically start the emulation on power up and for selecting drive images if more than one is desired.
The board may be powered through the drive power connector J5 or the BeagleBone barrel power jack. It can't be powered by the USB connector.
The board has a bank of super capacitors to provide enough power to allow the software to cleanly shut down the BeagleBone operating system when power is lost to prevent file system corruption and data loss. The board input is 12V with a DC/DC converter to generate 5V. If the backup power is not desired a pad is provided to allow the input 5V to power the board instead of the DC/DC converter.
The BeagleBone takes around 350 mA running and the emulation board fully populated is expected to take around 300 mA for total of .650 mA/3.25 W. It is expected that the capacitors should be able to run the board for at least 7 seconds after power is lost.
The capacitors are rated at 2.7V maximum. With 5 in series the theoretical rating is 13.5V. Due to mismatch in capacitance when charging the voltage will not divide evenly between the capacitors. U6-U10 clamp the voltage on each capacitor to 2.5V. With .3 volt drop across D1 the 12V input should be below 12.8 volts to prevent the entire string of regulators trying to clamp the input voltage. Resistors R8-R12 prevent the mismatch in capacitor leakage current from unbalancing the voltage on the capacitors.
R13 sets the peak charging current and limits current through voltage clamps on capacitors. The 10 ohm resistor sets peak current to about 1.2A. The value was picked such that if the capacitance of one capacitor is 20% greater than others will keep the current through the voltage regulator under the maximum rated current. Adjust the value if a different peak charging current is desired. Make sure the part chosen can withstand the peak power dissipated. With this resistor it will take about 70 seconds to charge the capacitors to 90% of final voltage.
Super capacitors were chosen since they are expected to be much more reliable than batteries though it does increase the cost. As an alternative some people have attached a battery to their BeagleBone. Since when on battery 5V won't be provided to the termination resistors all the control lines will go low. This can be interpreted as a write. Switching RN1-RN3 to 150 ohm bussed resistors powered by 3.3V will prevent this. This will require cuts and jumpers. I have not tried the battery method of powering the board. There are other options such as a push button to shut down or if nothing is important on the drive reflashing the beaglebone if the flash gets corrupted.
J7 is provided to allow switches for controlling operation or displays for status. No software support is currently provided for the expansion connector. For my usage I only desire to select between a few images. I am planning to hook up a rotary switch that I can use to select the image at boot time. I was also going to see if a wireless USB adapter gets enough signal inside the chassis. This will allow me to back up the emulation image and any other playing I wish. The USB connector ended up in a bad location so a short extension cable may be needed to get the USB WIFI closer to an opening for better reception.
The expansion connector uses the LCD pins so LCD/HDMI video will not work if the expansion connector is used. I suspect it won't work even if its not used due to the additional loading and that the MFM portion of the design uses the audio pins.
All signals must be 3.3V. 5V and 3.3V power is provided. With cuts and jumpers the unused pins on U2 and U3 can be used to level shift signals. Also note that expansion 10, 11, and 12 are on pins used to select boot device. These pins have 100k resistors to +3.3 or ground. Anything connected to them must ensure they still have valid logic level at power up either by limiting loading or with a lower value resistor. See the BeagleBone black system reference manual for interfacing information.
The write jumper P1 when removed ensures software errors can't cause writing to a drive being read. R7 prevents the write line from being seen as a low if the termination is not installed on the drive if this board is powered from the same supply powering the drive. Its value is high enough that it will not load down the write signal if this board is powered off while the drive still has power.
The EEPROM for shield configuration was designed in the board. Shields that are sold pre-assembled are supposed to have the EEPROM. It's not really useful for kit boards.