Rs232 comm between NVIDIA and Roboteq

[scoutingrobot]

Hello,

I measured the voltages:
Roboteq, Tx and Gnd: -9.19V
NVIDIA, Tx and Gnd: -0.2V

Why am I receiving a negative voltage near the NVIDIA side?
Shouldn’t it be 0-3.3V?

[scoutingrobot]

Hello,

I measured the voltages:

Between Roboteq, TX and GND: -9.19V
Between NVIDIA, TX and GND: -0.2V

Shouldn’t I receive 0-3.3V at this other end?

[scoutingrobot]

Sorry, in RS232 inverting mode, the voltage measured along the other side of the resistor is around 9V roughly.
The voltage is only getting dropped across the resistor and the diodes are not affecting the circuit in any form.

[SuperDroid]

This is expected. The diodes are for protection. As the documentation states, they are used to clamp the voltage between the resistor and the Jetson Rx.

The key to this circuit is changing the voltage observed by the Jetson Rx. It seems you’ve only checked the Tx voltage of each device.

[scoutingrobot]

So, should I run the code and try receiving something to check the voltage at Rx?
Currently, it is just 0V.

[SuperDroid]

Yes you can try that. Do you have access to an oscilloscope so you can observe the pulse train? Just measuring the voltage isn’t great for validating the logic level of communication lines.

[scoutingrobot]

Sorry, don’t have an oscilloscope.
What data can I send to see the motor controller respond?

[SuperDroid]

The manual has a commands reference starting on page 187.

[scoutingrobot]

I have attached the connection diagram below. Kindly, take a look and let me know if anything is incorrect.

• This reply was modified 2 years, 9 months ago by scoutingrobot.

[SuperDroid]

It seems your files failed to upload. Please email them to sdr@sdrobots.com.

[scoutingrobot]

Would a MAX232 chip work for communication?
I have tried it before with PC and PIC microcontroller and it has worked.

Only concern is would it bring it down to 0-3.3V logic levels.

[SuperDroid]

It seems like that would work. I’m not sure what logic level it supports.
I reviewed your picture and it seems you have a diode backwards. I couldn’t follow the wires since they go out of frame and are all the same color.

[scoutingrobot]

oh sorry about that. Have tried flipping the diodes in either direction but the voltage level at the Rx of NVIDIA still showed 4.95V which I think is a clipped voltage as it cannot take in excess of 4.95V

[scoutingrobot]

Hello,

I tried serial communication with USB from Roboteq to Jetson Nano, worked perfectly.
But the same with an adapter and the circuit on Pg 179 does not work at all.

Really stuck right now. Max232 is the last resort.

[scoutingrobot]

Got a voltage close to 5V using Max232.

Should I opt for Max3232 instead since it has 3.3V supply and might give a logic level of close to 3.3V ?

[Author]

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