You also need to fix the receive callback declaration and definition as suggested by John doe below in his comment of March 14, 2025 at 3:40 pm. The new incoming data where mac used to be is now a struct that has incoming mac, receiver mac and another val I don’t understand yet.

You need to change the onReceive function as suggested by John doe in the comment after yours posted March 14, 2025 at 3:40 pm.

Then use info->src_addr to refer to the sender’s mac if needed. It took me a really embarrassing amount of time to “fix” that update.

Your computer needs multiple available usb ports, of course. Then hook each chip up one at a time to an available port and look through the list in Tools->Port to find a port that shows output of your Serial.print statements on your Serial monitor. As you hook up more chips, under Tools->Port you’ll find new ports appearing. Set new chip to that port and check again that the correct Serial.print output statements are appearing in your Serial monitor. You can run at least 6 chips this way using Arduino IDE, I haven’t tried more.

If sending to an explicit mac address, an ack is in fact returned from receiver. If using broadcast address, no ack is returned. Thus broadcast is slightly faster but less certain. I don’t know what happens when sending to NULL (i.e. sends to all peers registered using esp_now_add_peer()).

@Friedhelm, possibly you are using sscanf() instead of strtok(). The former will stop at spaces, so will only read any char string until the first space, ignoring the rest of the string. strtok() will read until the next token (e.g. a comma if a comma-separated list of variables). Can you see the initial part of the string that comes before the first space?

Hi.
I’m sorry. But I’m not sure what can be the problem…
I’m not sure if it is related to some ESP32 specific model …

I’ve always used the same ESP32 model.

Regards,
Sara

Hello Sara,
I have two different boards.
One is:- Chip is ESP32-C3 (QFN32) (revision v0.4)
The other is:- Chip is ESP32-D0WD-V3 (revision v3.1)
I want to send data from the first to the second, but get exactly the problem shown by Nils, yes, I know, 5 years ago!
Then I had an inspiration. Why not try the other way round?
It works perfectly from the D0WD to the C3, but not from the C3 to the D0WD.
I have repeated the experiment, retyping the MAC address a couple of times, but the result is the same.
Any ideas?

I have the same problem as Nils (above). That eliminates the suggestions above. Any other ideas why we get this problem?

Yes.
That’s right.
Regards,
Sara