# Connector standard

This standard defines all hardware aspects of how to build a compatible device. It is based on DS-009 PX4 standard (opens new window) and DRONECAN Hardware design recommendations (opens new window) and aiming to be compatible with these technologies.

# 2. Connector Series

This standard intended for in-vehicle, cross-PCB usage. It uses the series which offers a latch lock mechanism at small size and a very competitive cost.

  • MOLEX 502585-0670 (opens new window)
  • JST SM04B-GHS-TB(LF)(SN)
  • JST SM06B-GHS-TB(LF)(SN)
  • 3PIN PWM connector B-2100S03P-A110
  • AMASS XT30U-M, XT30U-F, XT30PW-M, XT30PW-F, XT60-M, XT60-F
  • MCX coaxial 50 Ohm connector
  • USB Type-C UJ31-CH-31N-SMT-TR

# 3. Vehicle cable harness and electrical design concept

Top vehicle failure occurs due to bad electrical connections in wire harness. Common approach to decrease possibility of vehicle termination is in redundancy (backup) of part that may fail.

# Power lines

Firstly, it is recommended to backup power lines in wire harness. Although DS-009 Pixhawk Connector Standard (opens new window) recommends to use 4 pin connector (JST SM04B-GHS-TB(LF)(SN)) where the only one wire is responsible for power up a peripheral device, this concept offers to use 6 pin connector (MOLEX 502585-0670 (opens new window)) where at least two wires are responsible for the power delivery.

First reason:

Its possible to represent a wire assembly as a simple electrical circuit as shown in the picture below.

resistance

Where the summarized resistance of the circuit might be presented as:

  • Rcon * 4 + Rwire * 2 * length (for JST GHR-04V-S connector)
  • (Rcon * 4 + Rwire * 2 * length)/2 (for MOLEX 5025780600 connector)
Part Name Resistance
JST GHR-04V-S (opens new window) Rcon 50 mOhm contact resistance
MOLEX housing 5025780600 (opens new window) Rcon 20 mOhm
AWG#28 wire* Rwire 213 mOhm/m (opens new window)

*commonly uses wires for assembly.

As it is written in DS-009 Pixhawk Connector Standard (opens new window) the power voltage is 5 volts @ 1 amp, so we can calculate the voltage drop from the power source to the device, in case of minimum interconnections inside the vehicle.

Current Length Voltage drop
0.1 A 170 mm 27 mV
0.5 A 170 mm 126 mV
1 A 170 mm 272 mV
0.1 A 500 mm 41 mV
0.5 A 500 mm 206 mV
1 A 500 mm 413 mV

In case of using MOLEX 6-wire cable the voltage drop decreases:

Current Length Voltage drop
0.1 A 500 mm 14 mV
0.5 A 500 mm 73 mV
1 A 500 mm 147 mV

As a result it is recommended to use MOLEX 6-wire connectors instead of JST GHR-04V-S to assembly a vehicle where at least one branch of the network longer than 0.5 m.

Second reason:

Obviously, a fail possibility of 2 wires at once is less then just 1 wire. In any case let's take a look at the commonly used power up scheme

scheme1

If the Voltage regulator fails because of any internal problem than all NODEs will loose the power.

Now let's take a look at another approach described on the next scheme

scheme2

It does not matter if a NODE is mission critical or not if there is a problem inside the device it wont lead to vehicle termination.

It is highly recommended to use his own voltage regulator for vehicles with large network length.

Summarizing all of advantages of this approach:

  • Backup power lines
  • Length of longest wire able to be longer than 0.5 m
  • Fail of a single NODE does not spread to other nodes and doesn't led to the vehicle termination.

# Topology

It is highly recommended to provide two parallel connectors for each interface per device, so that the device can be connected to the bus without the need to use T-connectors. T-connectors should be avoided (opens new window) when possible because generally they add an extra point of failure, increase the stub length, weight, and often require more complex and expensive wiring harnesses.

It is better fo follow next recommendations for the bus topology design:

  • Separate into horizontal and vertical buses. Then have a bridge between them.
  • Use a SNAKE topology instead of T-shape.

can_chaining_non_redundant

The figure below demonstrates a bus wired according to the above recommendation.

can_chaining_doubly_redundant

The next figure shows a bus where the devices are equipped with doubly redundant interfaces. The same principles apply to a triply-redundant bus as well.

Unfortunately sometimes it is necessary to use T-connectors or star topology on bus. In this case its better use bus splitter.

# Reliability and Redundant interfaces

Mission critical and non-mission critical devices often need to co-exist on the same network. Non-mission critical devices are likely to be equipped with a non-redundant bus interface, which can create the situation where multiple devices with a different number of redundant interfaces need to be connected to the same network.

If multiple devices with a different number of interfaces need to co-exist on the same network, the following rules should be followed:

  • Each available CAN bus (DroneCAN supports up to 3) is assigned a level of importance (primary or backup).
  • All devices should be connected to the primary CAN bus.
  • Only devices with redundant interfaces should be also connected to the backup bus/buses.

The figure below shows a doubly redundant CAN bus, but the same considerations apply to a triply redundant bus:

redundant_can_bus

# 4. Connectors specification standard

# CAN

Recommended CAN transceivers: TJA1042TK/3 (opens new window) or TJA1051TK3/118 (opens new window) or LTC2875 (opens new window). Ensure to twist the wires.

# Molex 6-pins Cable (SMX R)

This pinout should be used for any CAN ports. In case of developing vehicle thet outline dimensions grater than 0.5 m its recomended to use self sufficient devices with voltage regulator on board. In this case port should be able to transfer needed power. Recommended connector is MOLEX 502585-0670 (opens new window) and it mates with MOLEX 6-pins cable (opens new window), and it can be assembled by you self using MOLEX housing 5025780600 (opens new window) and 6 pins 5025790000 (opens new window).

Pin Signal Max voltage
1 Vin 60
2 Vin 60
3 CAN High 60
4 CAN Low 60
5 GND GND
6 GND GND

power

power

# JST 4-pins cable (SJT R)

The Micro connector is intended for weight- and space-sensitive applications. It is a board-level connector, meaning that it can be installed on the PCB rather than on the panel.

The Micro connector is compatible with the Dronecode Autopilot Connector Standard. This connector type is recommended for small UAV and nanosatellites. It is also the recommended connector for attaching external panel-mounted connectors (such as the M8 or D-Sub types) to the PCB inside the enclosure.

In case of using low power devices and small vehicle. And in the way of compatibility with PX4 standards its recommended to use 4 pin JST SM04B-GHS-TB(LF)(SN) connector that suits with JST 4-pins cable (opens new window). And can be assembled using next PN: JST GHR-04V-S (opens new window) and pin SSHL-002T-P0.2 (opens new window).

Pin Signal Max. voltage
1 Vcc 5.5V
2 CAN High 3.3V
3 CAN Low 3.3V
4 GND GND

Devices that deliver power to the bus are required to provide 5.0—5.5 V on the bus power line. The anticipated current draw is up to 1 A per connector.

Devices that are powered from the bus should expect 4.0—5.5 V on the bus power line. The maximum recommended current draw from the bus is 500 mA per device.

Advantages

  • Extremely compact, low-profile. The PCB footprint is under 9✕5 millimeters.
  • Secure positive lock ensures that the connection will not self-disconnect when exposed to vibrations.
  • Low-cost, easy to stock.

Disadvantages

  • Board-level connections only. No panel-mounted options available.
  • No shielding available.
  • Not suitable for safety-critical hardware.

As alternative UCANPHY Micro patch cable (opens new window) can be used.

Photo of this type of wire presented below.

power

Mechanical drawing is presented here.

power

# Telemetry Port

This pinout should be used for any serial port. Cables should be 1:1 to the master and TX / RX as well as CTS / RTS should be crossed on the master side (e.g. a autopilot would have its RX port on pin 3, TX port on pin 2, RTS on port 5 and CTS on port 4).

Devices that supports flow control should use 4 pin JST SM06B-GHS-TB(LF)(SN) connector.

Pin Signal Max. voltage
1 Vcc 5.5V
2 RXI 3.3V
3 TXO 3.3V
4 RTS 3.3V
5 CTS 3.3V
6 GND GND

Ports not supporting hardware flow control should use 4 pin JST SM04B-GHS-TB(LF)(SN) connector that suits with JST 4-pins cable (opens new window). And can be aseembled using next PN: JST GHR-04V-S (opens new window) and pin SSHL-002T-P0.2 (opens new window).

Pin Signal Max. voltage
1 Vcc 5.5V
2 RXI 3.3V
3 TXO 3.3V
4 GND GND

# SBUS

Connector is compatible with JST 4-pins cable (SJT R).

Pinout is presented below.

Pin Signal Max. voltage
1 Vcc 5.5V
2 SBUS 3.3V
3 RSSI 3.3V
4 GND GND

# I2C port

Connector is compatible with JST 4-pins cable (SJT R).

Pinout is presented below.

Pin Signal Max. voltage
1 Vcc 5.5V
2 SCL 3.3V
3 SDA 3.3V
4 GND GND

# SPI port

Pinout is presented below.

Pin Signal Max. voltage
1 Vcc 5.5V
2 CLK 3.3V
3 MISO 3.3V
4 MOSI 3.3V
5 SS1 3.3V
6 GND GND

# 5. Internal Debug Connectors

# 1. This standard

For STM32 firmware updating using programmer-sniffer it suggested to use same SJT170R cable with SWD-NEEDLE adapter.

Pinout is presented below.

Pin Signal Max. voltage
1 3.3V 3.3V
2 SWDIO 3.3V
3 SWCLK 3.3V
4 GND GND

# 2. Other options

Its possible to update firmware using SWD-NEEDLE adapter and SJT170DB wire in case of usage Zubax probe (opens new window) debugger.

Pinout of connector with part number SM06B-SRSS-TB is presented below.

Pin Signal Max. voltage
1 3.3V 3.3V
2 TXO 3.3V
3 RXI 3.3V
4 SWDIO 3.3V
5 SWCLK 3.3V
6 GND GND

Mechanical drawing of this cable presented below.

debug

# 6. Wire assemblies

Its used Silicone Rubber Cable UL3239 (opens new window) standard wires for wire assemblies. Initial standard is presented on ul.com (opens new window) web site. Its highly recomended to use Q/IRMV2-2008, UL758 (opens new window) (or UL758-2000REV (opens new window)) for wires in future.

Cable characteristics:

  • Type: two twisted pairs, or one twisted pair plus one straight pair
  • Twisting pitch: 0.3–1 twists per centimeter
  • Wire gauge: #28 AWG
  • Wire strands: 7/0.12TS or 16/0.08TS
  • Wire Insulation thickness: 0.42 to 1 mm
  • Conductor material: copper

The following table provides an overview of the currently used connector types.

Connector name Base connector type Bus power compatible standards
JST 4-pins cable (SJT170R) JST GH 4-circuit 5 V, 1 A Dronecode Autopilot Connector Standard (opens new window)
JST 4-pins cable (SJT250R) JST GH 4-circuit 5 V, 1 A
JST 4-pins cable (SJT500R) JST GH 4-circuit 5 V, 1 A
Molex 6-pins Cable (SMX150R) Molex 6-pin 30 V, 2 A This standard
Molex 6-pins Cable (SMX250R) Molex 6-pin 30 V, 2 A This standard
Molex 6-pins Cable (SMX500R) Molex 6-pin 30 V, 2 A This standard
Molex 6-pins Cable (SMX100R) Molex 6-pin 30 V, 2 A This standard
SJT170DB JST GHR-04V-S to SHR-06V-S Zubax probe (opens new window)

# 7. Wire mating

Here you can find manufacturer part number of connectors it self and its mates.

Type MP Suitable Wire Type MP
CAN-LV, UART, I2C, SWD JST SM04B-GHS-TB(LF)(SN) JST 4-pins cable (opens new window) JST GHR-04V-S (opens new window) and pin SSHL-002T-P0.2 (opens new window)
PWM B-2100S03P-A110 Dupont 3-Pin Connector
SWD JST SM04B-GHS-TB(LF)(SN) JST 4-pins cable (opens new window) JST GHR-04V-S (opens new window) and pin SSHL-002T-P0.2 (opens new window)
CAN-HV MOLEX 502585-0670 (opens new window) MOLEX 6-pins cable (opens new window) MOLEX 5025780600 (opens new window) and pin 5025790000 (opens new window)
MCX Female MCX coaxial 50 Ohm connector Male MCX -
DEBUG SM06B-SRSS-TB(LF)(SN) SJT170DB SHR-06V-S and pin SM06B-SRSS-TB