Uno as a serial converter, fails

Using Arduino Networking, Protocols, and Devices
1

Hi,

While i don't have an USB-serial converter on hands to troubleshoot a fingerprint sensor, i decided to try and utilize Uno as one. However my attempt fails. To troubleshoot this new problem i set up a test.

Ard2 has a few rows of code: read serial at 57600 speed, wait shortly and echo the same back to serial. This works ok when Ard2 is directly connected to PC.

Ard1 contains blank code, RST-pin grounded.

Ard1&2 has RX and TX interconnected. Tried also switch them over, but i guess tx-tx and rx-rx should be the way to go.

When the chain of Arduinos, and at the Arduino IDE terminal hit enter with a message, i can see both boards led blink simultaneous once. Implying both might receive the serial message, but now nothing echoes back to PC screen.

What might be the problem? Thanks.

ardSer

2

I think it should be Tx Ard1 -> Rx Ard2 and Tx Ard2 -> Rx Ard 1.

That's an interesting idea, and I can't immediately see why it wouldn't work.

image
image1435×685 269 KB

Nothing else seems to be connected to RESET2 so the ATMEGA8U2 should work as a serial - USB interface. The 328P is reset so IO0/IO1 should be high impedance. Hopefully someone else reading this topic will know why it doesn't work.

3

Hint: When something talks nothing happens until somebody hears. Consider Tx the mouth and Rx the ear. Two Rx connected will hear nothing while two Tx connected and talking there is nothing to hear them.

4

Thanks for replies, guys.

rx-tx setup is as mute as tx-tx. the only difference is with rx-tx the Uno indicator led won't light up for serial burst in either boards, while tx-tx does.

i reasoned Ard1 be now a dumb pass-through proxy; and the rx-tx pair being pc and Ard2. Might be wrong thinking. Ofc normally, out of RST-mode, rx listen tx.

I might tomorrow add a LCD to Ard2 to see if the message reach there.

5

Yes you are right. I was thinking about it, and realised I'd been wrong in my earlier post. I'm sorry about that.
To confirm my new thoughts are the same as yours:

  1. Ard1 has its 328P disabled with reset.
  2. You are using the ATMEGA8U2 on Ard1 as a USB Serial adaptor for Ard2
  3. You should connect Ard 2 Tx to Ard 1 Tx so that the ATMEGA8U2 behaves as if Ard 1 Tx was active.

One thing I'm not sure about is connecting Ard 1 Rx to Ard 2 Rx. It depends what Ard 2 Rx is. If it's Ard 2 D0, then you would be shorting the outputs of both ATMEGA8U2s on Ard 1 and Ard 2 together. On the other hand, if you are using software serial on Ard 2 then it would be okay to connect. Ard 1 Rx to Ard 2 Rx