GND Between IND I/O and Mega 2560 Screw Up

Hello. On previous post, I asked about how to communicate between IND I/O and Mega 2560 through serial. I ended up cutting pin no.5 of the IND I/O chip to disable RS485 and connected pin D0 (RX) and D1 (TX) from IDC14 expansion port to Mega Serial 1. Initially, the serial output contain a lot of garbage data until I connected the GND pin of Mega 2560 to IND IDC Pin ISO 2 (GND).

The serial communication is perfect but I noticed that when I disconnect power completely to the IND I/O but leaving the power to Mega 2560 ON, the LCD of the IND I/O will be on too although dimmer than usual. It seems like the IND somehow got power from Mega 2560's GND port. This behaviour is gone if I disconnect the GND link between the two devices. At first, I ignored this issue but today it seems like it screwed up the IND Top Board. The PWM pin D5 from the IND I/O stopped working. I confirmed by replacing the IND I/O with a new one, uploaded the same sketch and the stepper motor worked again. Now I have not connect the GND Mega to the new IND I/O GND as I am afraid it will screw up again.

I used a 9V 1A switching adaptor for the Mega 2560 and Autonics 24Vdc PSU for the IND I/O. Can anybody please let me know what did I do wrong? I am not from EE background, so I totally have no clue here.

I just wasted a precious IND I/O. I hope someone can help me out, please... Thank you.

Albert Tobing
Albert Tobing
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Asked on 5/22/17, 10:15 AM
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It can be that by using two PSU which are not isolated from mains something went wrong.

Try measuring voltage between the two grounds without connecting and then do your math.

It is possible that you connected the two mains plugs in a way that the reference for the two PSU be 230V apart.

You could find out the neutral for both supplies and connect them so that the difference between the two grounds is minimal.

More safe would be that at least one of the two PSU has a transformer.

Or you can use a line isolator chip on the serial line.

Stefano Giuseppe Bonvini
Stefano Giuseppe Bonvini
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Answered on 5/22/17, 11:30 AM
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Hello Stefano. Thank you for responding. I tried measuring the potential between two GND and the result is as follow: IND ON & Mega ON : 0.26V IND OFF & Mega ON : -4.76V --> This is when IND LCD on. IND ON & Mega OFF : 5.1V. As I am not from EE background, can you tell me what does those values mean?

Albert Tobing
on 5/22/17, 12:51 PM
Didi you have the serial pins connected or nothing between the two boards?

Il 22 maggio 2017 alle 14.51 Albert Tobing <albertlt@industruino.com> ha scritto:

Hello Stefano. Thank you for responding. I tried measuring the potential between two GND and the result is as follow: IND ON & Mega ON : 0.26V IND OFF & Mega ON : -4.76V --> This is when IND LCD on. IND ON & Mega OFF : 5.1V. As I am not from EE background, can you tell me what does those values mean?

--
Albert Tobing
Sent by Industruino using Odoo about Forum Post GND Between IND I/O and Mega 2560 Screw Up (353)

 
Stefano Giuseppe Bonvini
on 5/22/17, 1:04 PM

Yes, I did have serial pins connected during measurement. 2 cables, 1 TX and 1 RX. Mega & IND GND connected to DC multimeter.

Albert Tobing
on 5/22/17, 1:20 PM

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Asked: 5/22/17, 10:15 AM
Seen: 500 times
Last updated: 5/22/17, 11:30 AM