Wiring multiple Roboclaw with Nvidia TX1

[henryacev]

Hi

I'm trying to wire two roboclaw to a UART provided by a Nvidia Jetson TX1, but I have some questions

1.)Based on the user's guide manual a resistor between the MCU RX (In this case the Jetson Nvidia) to S2 and S1 to TX, and the 5V from the Roboclaw to MCU and gound
then the other roboclaw S2 to the same line to RX and S1 to TX and ground .

my question is that if I want the Roboclaw to use its own power for logic and not use the MCU 5 V output, how do I wire this?

Thanks

[Basicmicro Support]

1. If you are only controlling one Roboclaw(not multiple units on a bus) then you wire the MCU TX and RX directly to S1(to MCU TX) and S2(to MCU RX). The roboclaw outputs 3.3v signals on S2 and is 5v tolerant on S1.

To user seperate 5v power, just do not connect the 5v line from the MCU to the Roboclaw. You will still connect the ground wire between the boards though.

[henryacev]

Thanks, but I want to connect two Roboclaw with one serial

in this case can I use the power from the Roboclaw but not from the MCU? despite the diagram (see Roboclaw user manual Page 38)

in this case can I use the MCU 5V and the pull up resistor to RX but not having connected the 5V to the Roboclaw

Thanks

[Basicmicro Support]

1. Confirm the NVida has 5v tolerant I/Os. If not use a 3.3v pullup instead.

2. It shouldnt matter if you are using a pullup from Jetcon power or from the Roboclaw 5v rail(unless Jetson is not 5v tolerant). If Jetson is not 5v tolerant you will need to pullup from the Jetson power rail.

Yes you can use a pullup from the MCU power without having a common 5v. Only a common GND is required.

[henryacev]

Hi

I wonder if you have any diagram showing this type of connections (without having a common 5V)

Thanks

[Basicmicro Support]

The wiring is shown in the manual on page 47. You do not need to have the 5v going to the controling MCU from teh Roboclaw as shown in the diagram. You just need the GND,TX and RX. However that MCU must be 5v tolerant or you could damage its I/O pins.

[henryacev]

Great, I about to complete my design from a Jetson TX1/Orbitty carrier board to three Roboclaw controllers under one single UART, on where the MCU has a pull up resistor on the 5V (I'm using a logical level shifter for RT/TX to 5V TTL)

however I need to confirm if the vale of the resistor, as the manual indicated that 1K to 4.7K, but I'm not sure which resistor value to use, could you please provide some guidance on this?

Thanks

[Basicmicro Support]

The stronger the pullup the faster you can transmit over a bus. However any value between 4.7k and 1k should be ok. What ever you have available.

Without seeing your circuit I cant say the logic level converter will work. When the roboclaws are setup for multi-unit mode they only pull the line(S2) low or let the line float(to be pulled up by the pullup resistor). That is how a bus works. A level converter is usually expected both low and high input signals that it then converts to the correct voltage levels.

The Roboclaws(or any bussed communications) must work this way when multiple units are conencted to the same pin since if they did not they would short each others I/Os when transmitting(eg one would be holding the line low while the others were trying to hold the line high).

[henryacev]

I had published my pcb diagram is very rudimentary you can find the link here one drive



https://1drv.ms/f/s!ApnM6Kx0frMEgQWOHBlMhBtoarg0

as for the resistor I have a 4.7 K, but, I’m thinking in replaced it for 1K , as for ground in the design I had removed the ground fill for easy visualisation

Thanks

[Basicmicro Support]

Which orientation are the RX and TX labels in relation to. RX to the Roboclaw or to teh UART?

Im assuming it is in relation to the UART so RX is the transmit(eg S2) from the Roboclaw to the UART. If so it looks correct though it is hard to be sure since some traces pass under each other that look to not be connected to each other while other traces pass under each other and are connected to each other.