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Partly offtopic - LCD --> Relay --> Power

Hi to all.

I've started to create schematics for PCB board that will be plugged onto arduino mega board. All pins are set on bottom double connector to simplify pcb design and all power( for arduino board / LCD, coin machine / relay/ keypad etc.) will come from this board. Main external power source will be 12V transformer ( cca 40W, standard ).

-------------------------- When i was testing the whole project i run on one possible problem. If i power arduino board ( for now, still over USB ) system starts OK and welcome message is displayed correctly, but when i plug power for relay ( which is powered from external 12VDC power adapter *for now*),LCD start to output random characters and signs. This will not happen if i start relay power source, first.

I dont know if this will happen when the PCB is done and when you will have one mayor power source,but it could be a problem..

In end effect, i can start reley first and then arduino, but i dont know why is this happening. Relay is connected over BC547 and diode so there shouldn't be any problem.

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2.)I'm using sainSmart arduino mega board. What is the optimal external power source for this board ? Can i power it with 9V or maybe 12V ?. On they web site is mentioned that there is a voltage range from 7-12V so 9V should be optimal solution ?. Any practical suggestions ?
Reply to
gm
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Most Arduino boards I have seen can be directly powered by a 5v source. The 9v etc is when the board is powered through the DC power socket which feeds a 5v regulator. Have you commoned the grounds of the Arduino and the 12v supply ?

Reply to
Rheilly Phoull

That's hard to follow. A simple picture of the output part would help. AFAIK arduino's output only 5V and need only that to run, powering it from more voltage, means a voltage regulator somewhere.

If you need more voltage to turn something on, then a separate power supply for that perhaps. Depending on the load that could be a single transistor.

George H.

Reply to
George Herold

Hi guys, sorry for late reply. This is the board that am using ( please look at characteristics )

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The module should be fully independent and it will be powered from external AC source (transformer ). The board that will be placed onto this arduino will have: - 5V - 9V - 12V DC outputs,because of different external parts that need this kind of voltage. But what i dont get is the operating voltage range of arduino board. From 7 - 20V.

So according to this, 9V would be some optimum solution. If you can please check this part fist, then i can explain in more details..

Reply to
gm

My guess is that the relay powering up is causing the processor to crash, probably by spiking the supply. How is the relay driven? Is there a flyback diode across the coil? If that doesn't mean anything to you, Google 'relay flyback diode'.

Cheers

--
Syd
Reply to
Syd Rumpo

The Arduino has an onboard linear 5 volt regulator on the power jack. You need to allow for the drop across the regulator so 7V is the minimum, anything above that just increases the dissipation of the regulator. Use of 9V is common because 7V supplies are not so common.

Reply to
Dennis

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