LynxSchematic

Lynx HIB (Hardware Interface Board) Schematic

This repo contains a reverse engineered schematic of and info on the Lynx HIB (REV Robotics Expansion Hub, and the Expansion Hub part of the Control Hub). This was done with a multimeter; it may have some errors.

The schematic itself is in the pcb directory. Photos can be found in the photos directory. Notes on repairs can be found in the repair notes directory

PCB versions

This schematic was created from a revision 2.3 Lynx HIB. This revision uses a Bosch BNO055 IMU and still includes an IMU in Expansion Hubs. Control Hubs and Expansion Hubs of this revision only differ by the inclusion of a compute board. Newer Control Hubs (sold after September 2022) seem to use a revision 2.4c or 2.5 HIB and have an Bosch BHI260AP IMU. The IMU section of the schematic has both in revisions's in it. Other sections seem to be the same aside from some component supplier changes and some additional zero ohm resistors around the compute board header. These zero ohm resistors aren't included in the schematic. I have not seen inside an Expansion Hub without an IMU (those sold after December 1, 2021), so I don't know how accurate this schematic is for them and how were changed from revision 2.3.

References

• Expansion Hub IMU Removal Notice
• Control Hub and IMU differences

Firmware

MCU

The MCU firmware can be found on REV's website.

Notes on replacing the MCU

• Use lots of flux for each step
• Use a pre-heater or heated plate to preheat the board for removal and replacement. The amount of copper on the board makes the MCU hard to work on otherwise
• Use hot air to remove the MCU. Even a cheap hot air gun without temperature control will work
• Try not to overheat the MCU while soldering
• Check the 3.3V rail for shorts by measuring the resistance across C63. If there are any at this point there are other problems on your board
• Tack in the corners of the new chip and drag solder the rest of the pins
• Once soldered in, do a visual inspection for poor solder joints or shorts between pins
• Next, check the 3.3V rail for shorts again. If there are any shorts the inspect the pins again and reflow and problem area.
• Apply power to the board and check if the 3.3v rail has come up to 3.3v
• Check that there is 1.2v across C28, C30, or C34 to check that the core voltage rail has come up. If not try to reflow the pins again.

First Upload

The first upload must be done with a debugger.

A method for uploading follows:

1. If your HIB's revision is > 2.3, solder on a JTAG connector or some leads
2. Acquire a "FTDI FT2232H Mini Module" to use as a JTAG debug probe. A genuine one from FTDI has a better chance of working reliably. Alternatively, use an ST-Link from STMicroelectronics. An ST-Link v2 was tested but a V1 should also work, but it may need a config change.
3. Connect the Mini Module or ST-Link to the HIB. They can be cleanly connected by making an adapter out of some 0.1" pitch header and half of a pre terminated cable sold by Molex that connects to the HIB's JTAG connector. See below for the cable's part number. The pinout of the JTAG connector can be found in the schematic. Connect
   • GND to GND
   • TCK/SWCLK to ADBUS0
   • TDI to ADBUS1
   • TDO to ADBUS2
   • TMS/SWDIO to ADBUS3
     Or with an ST-Link:
   • GND to GND
   • TCK/SWCLK to SWCLK
   • TMS/SWDIO to SWDIO
4. Download OpenOCD or install it from your favorite package manager. This flashing process has been tested with OpenOCD v0.12.0, but newer versions should work
5. Download the config files for the Lynx HIB and Mini Module or ST-Link here
6. Connect battery power to the board
7. Run openocd -f ftdi_lynx.cfg -c "program <path to firmware file> reset; shutdown" or for an ST-Link run openocd -f stlink_lynx.cfg -c "program <path to firmware file> reset; shutdown"
8. Remove power from the board and reapply it. This allows the bootcfg register programming to take effect

Subsequent uploads

If firmware has be uploaded before it can be upgraded the same way or with the bootloader by using REV Hardware Client, the FtcRobotController app, or DuckUpdate. TI's LMFlashProgrammer will also work if the MCU is restarted into the bootloader. This can be done with DuckUpdate or with REV's node-expansion-hub-ftdi.

FT230XQ

There is no firmware for this device, but it needs to have its config updated. Its config holds the serial number for the HIB, so when writing the same config to many devices be careful to not overwrite the serial number field. As well, it is connected to the reset and bootloader entry pins of the MCU and by default it will drive these pins to ground which will hold the MCU in reset forever. To fix this the CBUS pin modes of need to be changed to GPIO. The easiest way to do this is with FTDI's FT_Prog utility, but it also can be done with libftdi or FTDI's d2xx library. To update the modes with FT_Prog, connect the device to a computer running the program, edit Hardware Specific -> CBUS Signals to all be GPIO, and save the new config to the device.

BNO055 IMU

The BNO055 IMU has built in firmware from Bosch. It can be updated, but it isn't intended to be replaced by user firmware. If the IMU has to be replaced whatever firmware that ships on the IMU from the factory will be fine.

BHI260AP IMU

The BHI260AP IMU has some built in libraries and a bootloader stored in ROM, but the user has to supply firmware. It is either supplied by the host device or it is read from an external SPI flash. On the Lynx HIB an external W25Q64JWSSIQ SPI Flash is used. The flash contains the same data across devices, so it probably doesn't have any device specific calibration in it and if the flash has to be replaced the data from one HIB's flash can be copied to another's

Components

• A large chunk of the passives are in a 0603 package
• Aux Shunt resistors are 20 mΩ (milliohm) in a 2512 package. P/N - Panasonic ERJ-M1WSF20MU

ICs

Diodes

Transistors

Many of these have labels with more characters listed, but those parts are date codes.

Connectors

Fuses

All from Bel Power? Bel Fuse? They are green.

Other

Mystery Components

• D2 - Different from revision 2.3 to revision > 2.3
• D3 - Maybe ESD Protection Diode LittelFuse SMF17A
• All the capacitors
• L1
• Y2 - 16 MHz main oscillator
• Y1 - revision 2.3 IMU oscillator. 32.768 KHz

Notes about the board

• The board seems to have more than two layers, so the creation of a schematic by observation wasn't possible.
• Make sure to not touch the 3.3v buck converter circuitry while the board is powered as the voltage reference can be thrown off which makes the 3.3v rail spike above 3.3v and blow stuff up. It's happened ...
• The 5V rail is not always on. The buck converter IC's enable pin is tied to a GPIO on the MCU. It won't enable without an MCU in place with the correct firmware

Compute board header (J18)

The header that connects to the compute board (if equipped).

Pin numbering:

 1 - - 40
 2 - - 39
 3 - - 38
 :     :
 :     :
20 - - 21

The pinout of the connector on the compute board can be found on page 16 of the 96Boards CE Specification Version 1.0.

• The compute board of the Control Hub is based off this specification, see gm0 for details

Bus transceivers

A is Compute Board Header - 1.8V
B is System - 3.3V
Eight channels

MCU connections

Overall temp sensor - in MCU
3.3V voltage sense - doesn't exist

FTDI FT230XQ

PB1 (Bootconfig enter bootloader) FT230X Pin 11 (CBUS1) and TP3 (NPRG)
RST FT230X Pin 12 (CBUS0) and TP2 (NRST)
PJ7 FT230X Pin 5 (CBUS2)
PK5 FT230X Pin 16 (RTS) and Compute Board Header 36

Digital GPIO

• GPIOs are set as open drain pins and have pull up resistors
• Output and input are from the perspective of the lynx

Analog GPIO

VCCA and GNDA are just connected to VCC and GND
VREFA- is connected to GND
VREFA+ is connected to a circuit that makes 2.994V. This is derived from the TL431A datasheet by using the formula Vout = Vref * (1 + (R1 / R2)), which in the case of the HIB is 2.994 = 2.495 * (1 + (2000 / 10000))

5V rail

Voltage monitoring AIN23 (PP0) - Through resistor divider with two 10K resistors to divide voltage by 2.

Servo

Servo 5V enable PC6 - Has pull down

Battery

Voltage - connected to AIN22 (PP1) via a 1/6 resistor divider with 10K and 2K resistors
Current - Uses a high side current monitor IC with a 0.003 ohm shunt and 3K Rout resistor into AIN13 (PD2)

External oscillator

Called main oscillator by the datasheet
16 MHz