This is revision B of the MBPi which is a module for the MakerBus Project.

MBPi (Rev. B)

An image of the MBPi Revsion B is shown below:

Table of Contents

• 1.0 Schematic
• 2.0 Design Files
• 3.0 Errata and Notes

1.0 Schematic

The schematic is available as either a .pdf file or as a .svg (Scalable Vector Graphics) file. The .pdf file should print reasonably well on a black and white printer. The .svg file is embedded below:

Connector N1 connects to the MakerBus (labeled "Robus" in the schematic). N1 supplies unregulated logic power on LPWR1, LPWR2 with a ground return of LGND1 and LGND2. The voltage is fead into the 3.3 volt linear regulator U2 with filter capacitors C1 and C2. The CANH and CANL from N1 are fed into the CAN bus transceiver U1. The 24K resistor R5 provides slope control from U1. Jumper J1 can be jumpered to terminate bus with 124 ohm resistor R1.

20MHz crystal X1 and 22pF capacitors C3 and C4 provide a 20MHz time base for NXP LPC1754 microcontroller U3. Connector N1 is a combined JTAG and Serial download connector that connects to the various JTAG and serial ports of U3. Both NRST and NPROG are pulled up using 10K resistors R2 and R3. When NPROG is grounded and reset is triggered low, the microcontroller enters bootloader mode.

The Raspberry Pi can be powered either from its USB connector or from the 5V switching regulator U4. Power comes in on N5 and goes through protection diode D2, which prevents problems when power is accidentally connected backwards.

{talk about why there electrical isolation between the RaspPi and MBPi.}

2.0 Design Files

This board was designed using KiCAD. A complete KiCAD archive of board is found in raspi.zip. ("Raspi" was the original name of the board before it was renamed to "MBPi".) When this file is unzipped, the KiCad project file can be found down in robus/raspi/rev_b/raspi.pro. Various shared .mod and .lib files are kept in the robus directory. All Gerber and drill files are generated using KiCad.

3.0 Errata and Notes

The following errata and notes have been recorded:

• R8 points to C10; the real R8 is between R8 and C10.
• The footprint for D2 is confusing. The diode got installed backwards. Improve the footprint.
• U5 Pin 8 should be connected to N3 3V3 (pin3 1,17), not 5V as shown in the schematic!
• The power traces for U4 are a little close to to vias, one another, etc.
• The Raspberry Pi folks took all the NC pins on the Raspberry Pi P1 connector and hooked them to power pins. Thus, the following additinal connections need to occur:
  • N3-01 3.3V
  • N3-17 3.3V
  • N3-02 5V0
  • N3-04 5V0
  • N3-06 GND
  • N3-14 GND
  • N3-20 GND
  • N3-09 GND
  • N3-25 GND
• R9 is connected to NC on RasPi connector, which is wrong.
• It would be nice to see the console output on boot-up.

This last issue needs more discussion. The Raspberry Pi can only connect one UART to its P1 connect. One of those UART's is used for console output and the other one has more handshaking signals (CTS, DTR, etc.)