R4 Minima not running off Vin

Official Hardware UNO Family UNO R4 Minima
1

I replaced an Uno R3 with an R4 Minima, but it refuses to run when powered on Vin. The R3 worked fine in this circuit. The R4 works on USB power but not on Vin; the power LED comes on but nothing else happens. I'm using the Vin pin rather than the barrel connector.

I used a multimeter to check the voltages and a scope to see if there's any LF or HF noise on the power buses. Vin reads a steady 11.4v (powered by a 12v regulated supply and a diode to guard against reversed polarity). The 5v and 3.3v buses read at the correct voltages as well. But the R4 refuses to boot even with all the external circuitry removed.

Any idea what could be causing this?

2

Post a link to the board's schematic.

3

What does "refuses to boot" mean? Have you uploaded working code, like the "Blink" program, via the USB connection?

Make sure that code does not include a line waiting for the Serial connection to be made, e.g. while(!Serial);

From the schematic it is clear that if 5V is present on the 5V pin, and since the R4 runs on USB power, the processor should be running. Push reset to restart.

4

Never mind, it turned out to be a software issue... and it was indeed the serial line. The code waited for Serial to initialize, which never happens on the R4 when it's not connected to a computer via USB. I added some code to use Serial1 in case this runs on an R4 (the code will likely be running on a variety of devices).

Thanks for the quick assist! I'm kinda new to the R4s

5

I use delay(2000); instead, which usually works as well as while(!Serial);.

You will encounter this problem with any Arduino that has a native USB connection.

6

In another thread KurtE provided a nice solution ... :wink:

... has basically introduced a timeout mechanism on the serial connection ... If it happens within N msec, fine, otherwise you continue anyway. :slight_smile:

Guglielmo