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Using external power with sensors and LCD etc


HBarkerNZ
(@hbarkernz)
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Joined: 9 months ago
Posts: 22
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Hi There,

I'm fairly new to having other power involved in my project but I'm getting there. I have my 110v relay bank (8 channel) powered up using an external 5v buck convertor so that it is fully isolated and using the optocouplers

. What I'm wondering, should I be trying to keep the main power draw for sensors off the arduino and on the power supply ? If so, when I substitute the VCC and ground from the arduino to the power supply (for my LCD as an example) it stops working. I figure this must be a grounding issue. I did try and figure this out myself once and it caused me to let the magic smoke out of my ArduinoMega so now I'm going to ask before trying again.

Specific question, the LCD backlight is the major power draw on the device, the LCD part is negligible. Is there a way for

me to power the backlight off my power supply and still receive data and run it on the i2c bus ?

PXL 20210207 191206799
PXL 20210207 191230811
PXL 20210207 191211873

Above is the LCD device, it is an 20x4 LCD, with an i2c "thingy" on the back that I soldered on.

Haydz


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codecage
(@codecage)
Member Admin
Joined: 2 years ago
Posts: 1089
 

I would be sure to connect the ground on the Arduino and the ground on the power supply.  The 5V VCC for the LCD/I2C connector then comes from the power supply and the SDA and SCL signals come from the Arduino to the LCD/I2C connector.

At least I think that is what you are asking if I am understanding you question.

SteveG


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HBarkerNZ
(@hbarkernz)
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Joined: 9 months ago
Posts: 22
Topic starter  

@codecage thanks ! I thought I did that last time but maybe I did something else. I'll connect the grounds and see how we go.

I think you have what I'm trying to achieve down just right.

Haydz


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codecage
(@codecage)
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Joined: 2 years ago
Posts: 1089
 

@hbarkernz

Yeah nothing should go wrong connecting the grounds together, but you did mention a 110V relay bank that does give me some concerns.

SteveG


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HBarkerNZ
(@hbarkernz)
Eminent Member
Joined: 9 months ago
Posts: 22
Topic starter  

So I don't think I understand grounding properly. I understand that it is closing the circuit typically. The 110v is completely isolated from everything else. I'm using an optocoupler based 8 channel board and I have the optocouplers powered by the arduino, but the relay side is powered from the 5v power supply.

I am okay with the fact that I can join the grounds of my 5v power supply and the ground of the arduino, however these are the same voltage. What would be the case if it was a 12v power supply or even 24/48 which is way above the arduino's ability. Can you join grounds of differing voltages ?

Side note, if Bill was considering a beginners video, I'd love to see one that explained grounding.

Haydz


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HBarkerNZ
(@hbarkernz)
Eminent Member
Joined: 9 months ago
Posts: 22
Topic starter  

Ok, so I joined the 5v grounds, and yes, your are correct that now it is drawing it's power from the power supply, and my text is showing up correctly. I don't fully understand but I guess I can do some googling 🙂

Haydz


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codecage
(@codecage)
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Joined: 2 years ago
Posts: 1089
 

@hbarkernz

It gives you a common ground, both for the 5V going to your Arduino from the USB interface and the 5V from your external 5V supply.

SteveG


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