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Tropic VMU Advanced Topics

This page describes various topics for advanced users.

Ethernet

Warning

For those with a Tropic VMU rev.B baseboard the RJ45 is non-fuctional, please use rev.C or later for ethernet

Ethernet 3x2 Socket + Pins

The ethernet board-to-board connection is a 3x2 socket with a 2mm pitch. Conventional 2x3 2mm pitch female headers should work fine but male headers have to be taller (~ 8.5mm) PJRC provides Pins & Sockets with the correct size.

As alternative you can also get these Pins from a distributor:
Samtec MTMM-103-10-T-D-355

Or these sockets:
TE 2314820-6
BOOMELE(Boom Precision Elec) 2.0-2*3P

Real-time Clock (RTC) Circuitry

A RTC allows you to keep track on time while the Tropic is powered off. This is done by powering the VBAT pin on the Teensy with a battery which allows the Tropic to keep track of time without power.

Tropic

The Tropic baseboard allows to 3 ways to power VBAT.

  • The combination of D1 and R18 are used to provide an adjustable trickle charge to a supercap or rechargeable battery

  1. SuperCap: By placing a supercap (DSK-3R3H703T414-HRL) on U5, diode (PMEG4002EB) on D1 and a 300Ω resistor on R18

  2. Rechargeable Battery: An external ML2020 rechargeable battery connected with a JST-SH connector for example the Raspberry Pi RTC battery. By placing a JST-SH 2-pin connector (SM02B-SRSS-TB (LF)(SN)) on BAT, diode (BAT43XV2) on D1 and a 300Ω resistor on R18.

  3. Primary Lithium Cell: An external CR2032 battery, By placing a JST-SH 2-pin connector (SM02B-SRSS-TB (LF)(SN)) on BAT, do not populate R18 and D1.

AUX Port

The AUX port is a 6-pin JST-GH Multi-function connector capable of the following configurations:

  • 1x UART using pin 2,3 and with pin4,5 claimed by RGB led
  • 2x UART
  • 1x UART with GPIO Handshaking
  • Quadrature decoder
  • 4x PWM
  • Crossbar trigger

JST-GH 6-pin pinout:

JST-GH Pin Label IMXRT Label
1 5V -
2 TX AUX B1_00
3 RX AUX B1_01
4 LED_R AD_B0_02
5 LED_B AD_B0_03
6 GND -

Note

Pin 4,5 on the AUX connector are shared with LED_R and LED_B from the RGB Led, you can only use either at the same time

This table shows the alternative MCU(Teensy Pin) functions available on AUX Port pins 2,3,4,5 above.

Teensy Pin Label IMXRT Label Primary Mode Alternative modes
8 TX AUX B1_00 LPUART4_TX FLEXPWM1_PWMA03, XBAR1_XBAR_IN14, GPIO2_IO16
7 RX AUX B1_01 LPUART4_RX FLEXPWM1_PWMB03, XBAR1_XBAR_IN15, GPIO2_IO17
0 LED_R AD_B0_02 XBAR1_XBAR_IN16 LPUART6_TX, XBAR1_XBAR_IN16, GPIO1_IO02
1 LED_B AD_B0_03 XBAR1_XBAR_IN17 LPUART6_RX, XBAR1_XBAR_IN17, GPIO1_IO03

PX4 AUX configuration

In the PX4 the AUX connector is configured by default to be a single UART with LED_R, LED_B used for the RGB led. Due note when connecting a 6-pin UART device you will need to unplug pin 4 and pin 5 to otherwise your device will receive interference from the RGB led PWM.

BMP388 End-of-life

The BMP388 Barometer availability is declining due to its EOL status. However the new BMP390 is pin-compatible and should just work fine as a replacement.