Relay/LCD power usage?

Hi all,

I'm using a 2 relay board with a 16x2 LCD (with backlight), and whenever I engage the relays the LCD display dims. I just put this into use today for watering my greenhouse and it seems to work, although occasionally the timer display get garbled (brown out on the chip?).

I'm using a (cheap) 500 mAmp power adapter to power the Arduino, but it does the same thing when connected to my MacBook.

Am I connecting something wrong maybe?

I use the LCD pretty much exactly as per the tutorials (I moved a few arduino pins to physically group all the LCD lines together), and for the relay it's just 2 digital pins directly hooked up to IN1 and IN2 on the relay board.

I tried adding 1k resistors between the Arduino control pin and the relay pin, but that seems to make no difference. The relay board already has resistors on it, as well as transistors, so I think the draw from the control pins is already very little.

But it does use the direct power from the Arduino board 5v pin to power the control part of the relay. (The circuit controlled by the relay is a 120volt plugin)

On the other hand, I suppose it could also be the LCD drawing near limit for power, causing any additional items to take it overboard maybe? I noticed that when I put an LED on the relay control pin (but I had forgotten to use a resistor so I blamed that at the time).

This is exactly what my relay board looks like:

If you have any ideas or suggestions, I'd love to hear it

Thanks,

-Nico

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dmaruska over 13 years ago

http://www.lemicro.cn/rar/SRD(T73).pdf is the PDF for the relay. It draws 71mA, but it seems to have a Transistor infront of the relay. If you have a datasheet of the board that would help.
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ntewinkel over 13 years ago in reply to dmaruska

Thanks for all the help, everyone

I didn't realize it was drawing 71mA per relay, thanks for that.
At 71 mA x2 + the power LED + 2x relay-active LED, that's a fair chunk of power used up by just the relay board. I'll try using just the one relay for the time being, as I was powering both relays at the same time just for the lazy factor of not guessing which outlet was active. It's all coming from the same power supply, so while it's not all coming directly through the digital pin, it is all coming from the Arduino board one way or another.

I'm powering the relay board from the 5v pin of the Arduino (Nano). The Arduino is powered by plugging the 500mA 5volt cell phone charger into the USB port of the Arduino.

I do have another cell phone charger that gives 700 mA, so I'll try that too.

I'll try to draw up a full schematic when I have time, but here is the one for the relay board:

Thanks,
-Nico
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R_Phoenix over 13 years ago in reply to ntewinkel

Try powering the Relay board from a seperate 5volt supply if you can. Just remember to common the grounds.
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terryking over 13 years ago in reply to R_Phoenix

Yes, as soon as you get to 2 relays, it's best to use a separate 5V supply for the relay power. Then you can use 4 or 8 relay boards with no problem..

Some how-to here: http://arduino-info.wikispaces.com/ArduinoPower.
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ntewinkel over 13 years ago in reply to ntewinkel

So I tried it with my cell phone charger, which outputs 700 mA and it all seems to be just hunkydory now. So it really does look like it's just power related.

I did also modify the code to only use the one relay, so it doesn't unnecessarily draw extra power there. But even then it was still having issues with the 500 mA power supply.

When I have more time I'll work on using a separate power supply for it, but for now the plants should get their water while I'm away for the next 4 days

Thanks for all the help and suggestions everyone!
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ntewinkel over 13 years ago in reply to ntewinkel

So I tried it with my cell phone charger, which outputs 700 mA and it all seems to be just hunkydory now. So it really does look like it's just power related.

I did also modify the code to only use the one relay, so it doesn't unnecessarily draw extra power there. But even then it was still having issues with the 500 mA power supply.

When I have more time I'll work on using a separate power supply for it, but for now the plants should get their water while I'm away for the next 4 days

Thanks for all the help and suggestions everyone!
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