Serial Port only working on USB power - MKR Wifi 1010+ MKR485 Shield

Official Hardware MKR Family MKR Shields
1

I setup two Arduino MKRs with MKR 485 Shields to send and receive data according to Sending Data Between Two MKR 485 Shields.

This works well, when both Arduinos are powered over the USB port, but when I power the Sending Arduino over an external power supply (GND, Vin) the Serial Monitor reads only gibberish.

I tried supplying 5V directly, supplying 12V to the GND and 7V-24V Screw connector on the MKR 485 Shield and supplying 24V to GND and 7V-24V Screw connector on the MKR 485 Shield.

Any idea what could be the reason for this behaviour?

2

please indicate more clearly what and where you connected...

Example

Power supply -- Board
+12v - > VIN
-12v -> GND

3

I tried the following pin setup:

Alternative 1:
Power supply -- Arduino WiFi 1010 (Sending):
+5V -> VIN
0V -> GND

Alternative 2:
Power supply -- MKR 485 Shield (Sending)
+12V -> VIN 7V-24V Screw Connector
0V -> GND (Screw Connector)

Alternative 3:
Power supply -- MKR 485 Shield (Sending)
+24V -> VIN 7V-24V Screw Connector
0V -> GND (Screw Connector)

4

Alternative 1 unlikely will work, because supply voltage (5v) is lower then the range (7-24v)
Two latter should be functional.
Do you connect GND between the boards?

5

Alternative 1 should also work in theory, because I supplied 5V directly to the VIN of the Arduino which is -0.3V - 5.5V.

Yes, I connected ISO GND pin from the Sending Arduino to GND pin on the receiving Arduino.
I also tried different variations of connecting GND between the two boards.

6

VIN is not DIRECTLY connected to the Arduino, see the board schematics.
Input ranges of the VIN pin and VIN screw connector are the same and designated near the connector - 7v-24v

7

Can you elaborate? Which VIN do you mean? On the shield or on the board?

8

Here is a schematic of Alternative 3, which also did not have any success.

WhatsApp Image 2022-11-24 at 19.46.32
WhatsApp Image 2022-11-24 at 19.46.321600×1131 93.7 KB

9

this both the same thing - it directly connected each other

10

The VIN of the Arduino MKR WiFi 1010 is connected to the VIN pin of the MKR 485 Shield. And as far as I can understand from the datasheet of the Arduino, VIN is -0.3 -5.5V.

https://docs.arduino.cc/static/dcee6dbcfacc810ae5a887ea9a0a56b3/ABX00023-datasheet.pdf

But anyways, this is not the main issue here. My problem is that the output of the MKR Shield only works on USB power, but not on external power.

Serial Monitor Receiving with USB power

hello 1
hello 2
hello 3
hello 4

Serial Monitor Receiving with external power

□□?
□□?
□□?
□□?
11

you misunderstood.
This is the range of allowable voltages that the controller can withstand, and not its supply voltage.
Really, it's ridiculous to expect that the controller will work from a power source of 1v or even 0v - both values are in the range -0.3 -5.5V

12

Ok so you are saying, the information in this support article of the arduino help center is incorrect?

VIN

Another way to power a MKR board is by supplying 5V from a regulated power source directly to the VIN pin. Just need to connect the positive wire from your power supply to VIN and the negative to GND.

13

==== incorrect content deleted ====

No, sorry, I was wrong.
I didn't look closely at the diagram.
Pin VIN on the board and on the shield are not connected

14

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