TReX JR: Can't connect with RS232

Hi there,

I’m using a TReX Jr controller board for a project, but I can’t seem to connect to it via RS232 with the TReX configurator (“Could not detect…”).
Here’s my setup: I’ve got 12V connected to the port thanks to an AC/DC adaptor. I removed the “Mode select”-jumper (so Serial is connected) and have nothing connected to any of the channels. Actually, I don’t have any jumpers on my board, which should be ok.

I connected my pc to the board by using a standard RS232-connector which goes to the three pins on my controller (Tx, Rx, GND). I connected it like in the following picture (top), Tx to Rx and vice versa:

I didn’t connect anything else, because my motors (not connected yet) should only work via serial commands, not with any RC/analog signal. Maybe here’s a fault?

When I ‘boot’ the controller the red light flashes a couple of times and then stays on.

When I want to connect to the controller with the TReX configurator now, it doesn’t work. If I follow the steps to update the firmware (these) and I press the ‘Connect’ button, the red light briefly flashes (which should mean it can make a connection?) but that’s all I get.
I tried by switching the Tx and Rx cables, but that didn’t do anything either.

Does anybody know what the problem might be and what I can do about it?



When you say you have 12V connected to “the port”, do you mean that you’re powering the board at 12V by connecting your adapter across VIN and GND? When the board first powers up in serial mode, you should see the red LED blink five times and then stay solidly on; is this what you still see?

I’m also confused as to why you were following the firmware update protocol and then clicking connect. Did you actually update the firmware?

Did you ever connect your RS-232 pins to the TTL pins on the TReX Jr (the pins the microcontroller is connected to in the bottom diagram you posted)?

Are you connecting the TReX Jr directly to your computer’s serial port via an RS-232 cable? Do you have access to a USB-to-TTL-serial adapter?

- Ben

Thanks for your interest.

  • With “the port” I do mean across VIN and GND :wink:. The red led does blink five times and than stays on, everything fine there.
  • No, I couldn’t update the firmware because it also said “Could not detect…”. It was then that I saw the red led blinking meaning there was some activity: in update-mode it alternates between red and green so it’s obvious when there’s any serial activity. With the red led constantly red it doesn’t blink when sending something to it.
  • I never connected it to the TTL-pins because there’s a big warning box about that in the manual :wink: (12V vs 5 V).
  • It’s connected directly to the pc with a standard 9-pins connection. I sadly don’t have access to a USB-to-TTL adapter.

My serial port from my computer is working btw, I recently used it to transfer data from a very old pc to my modern one.

I attached a picture from the current setup:

Could you post a close-up picture of the 3x1 connector you have plugged into the TReX Jr and a picture that shows how your cable connects to the DB9 connector?

Can you try a loop-back test with your serial cable? Disconnect it from the TReX Jr, short the cable’s TX output to its RX input, and see if you get back bytes sent with a terminal program like hyperterm.

- Ben

I finally got it, but I’m ashamed to tell you my mistake…

I had to connect pins 2 & 3 from my serial port… I used pins 2 & 3 of my female kable though, instead of the male connection of my pc (they’re not the same of course). Sooo stupid :blush:.

Thanks Ben for giving me the Tx-Rx loopback tip, because that’s how I could figure it out :slight_smile: .

Don’t feel bad; we all make mistakes like that. I’m glad to hear it’s working for you now!

- Ben