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[on:]

Hello , im an arduino beginner and i want to make a project which will need

1x Arduino UNO
1x Shield
2x DC Fan
1x keypad
1x lcd (2x16)
3x sensors
40x led

I dont know much from electronics and i want to guide me if you have time. I know that arduino and its shield want 5V@2A as mentioned here http://tronixstuff.wordpress.com/2011/01/19/tutorial-arduino-and-gsm-cellular-part-one/

So i will need 1 DC power supply that outputs 5V@2A and i will connect it to my shield as mentioned to the tutorial and it will power up the 2 boards.

Now my question is , how many other power supplies and what voltage should i need to power all other stuff ?

For example the (1) DC fan needs 5V@200mA and the lcd needs 5V@1A.

Can you advice me ? thanks !

[Reply #1 on:]

It all depends on how you want to wire it up.

If all the devices run at 5V, then you could use one single 5V supply which can provide *AT LEAST* the total amount of current draw for all the devices.

So, for 3 devices which are, for example, 5V, and 1A, 800mA and 120mA respectively, a power supply of 5V and at least 1920mA would be needed, so a 2A would just about do for that.  I like to add a bit of extra for leeway, so a 2.5A 5V supply would work for that example.

If you want to run different bits off different supplies, then work out what you want to group with what, and calculate the total current for that group, then apply the same rules as above.

If the voltages differ, say you have some 5V devices and some 12V devices, then you will need one power supply per voltage.  That might be completely separate supplies for say 12v and 5v, or a 12v supply which then feeds some form of voltage regulator system to provide the 5v portion.

In the former case, treat it like the multiple 5v supplies, but grouped by voltage, and work out the total currents.  If you want to feed from a 12V through a regulator, then you need to consider much more, including the efficiency of the regulator, the total current draw at 5V, the total current draw at 12V, the current draw the 5V would cause on the 12V via the regulator (different regulators work differently and cause different voltage to current ratios).

[Reply #2 on:]

So i will need 1 DC power supply that outputs 5V@2A and i will connect it to my shield as mentioned to the tutorial and it will power up the 2 boards.

Now my question is , how many other power supplies and what voltage should i need to power all other stuff ?

For example the (1) DC fan needs 5V@200mA and the lcd needs 5V@1A.

Can you advice me ? thanks !

Ummm...why can't they be connected to the same 5V power supply?

[Reply #3 on:]

Any of the boards or sensors need a low noise supply - for instance audio amp?   It's usually a good idea to avoid sharing a supply between digital logic and sensitive analog circuitry to reduce the noise from the logic - for instance a microphone amp should not share supply with
a microcontroller - noise levels of microvolts matter for microphone signals.

[Reply #4 on:]

Any of the boards or sensors need a low noise supply - for instance audio amp?   It's usually a good idea to avoid sharing a supply between digital logic and sensitive analog circuitry to reduce the noise from the logic - for instance a microphone amp should not share supply with
a microcontroller - noise levels of microvolts matter for microphone signals.

And sharing anything with an SD card is just asking for *buzzzzzz* trouble.

[Reply #5 on:]

And sharing anything with an SD card is just asking for *buzzzzzz* trouble.

i didn't understand this about the sd ! can you explain it ? im planning to connect a raspberry pi in future which uses an sd card...

Any of the boards or sensors need a low noise supply - for instance audio amp?   It's usually a good idea to avoid sharing a supply between digital logic and sensitive analog circuitry to reduce the noise from the logic - for instance a microphone amp should not share supply with
a microcontroller - noise levels of microvolts matter for microphone signals.

So you suggest to seperate the supply of sensors from other supplies right ? The board will be a gsm shield , and the supply/wiring is recommended from the tutorial... the sensors will be humidity digital sensors

If all the devices run at 5V, then you could use one single 5V supply which can provide *AT LEAST* the total amount of current draw for all the devices.

So, for 3 devices which are, for example, 5V, and 1A, 800mA and 120mA respectively, a power supply of 5V and at least 1920mA would be needed, so a 2A would just about do for that.  I like to add a bit of extra for leeway, so a 2.5A 5V supply would work for that example.

So i can have a 5V supply with 1A over the sum/total amps of the items in my project which requires 5V as one group , with A i will not damage something , i will damage only with voltage is that right ?

Thank you allo for answering

[Reply #6 on:]

the lcd needs 5V@1A.

That's some lcd.

Of them, the fan looks to be the trouble. I would put it on a different power supply, or to put some isolation there (a diode + cap for example).

[Reply #7 on:]

And sharing anything with an SD card is just asking for *buzzzzzz* trouble.

i didn't understand this about the sd ! can you explain it ?

SD cards are notorious for inducing huge amounts of noise into a power rail.  I have been working on an audio project (http://sf.net/projects/wavepro) and one of the first problems I had was how to keep the SD card's buzz away from the audio side of the circuit.  The buzz was so bad, if you connected a normal 8Ω speaker to the power rail through a capacitor you could hear it clear as day.  Yack.

[Reply #8 on:]

So you are telling me that if my sensors are analog , i will get wrong voltage by the buzz from other stuff right ? and that i have to avoid it like an sd card will effect an analog gas sensor

[Reply #9 on:]

So you are telling me that if my sensors are analog , i will get wrong voltage by the buzz from other stuff right ? and that i have to avoid it like an sd card will effect an analog gas sensor

It might.  It all depends on the sensors and how sensitive they are to power supply noise.

[Reply #10 on:]

So you are telling me that if my sensors are analog , i will get wrong voltage by the buzz from other stuff right ? and that i have to avoid it like an sd card will effect an analog gas sensor

It might.  It all depends on the sensors and how sensitive they are to power supply noise.

thanks i understood

[Reply #11 on:]

You should also take a look at this tutorial on de-coupling, adding capacitors or low-pass filters to reduce noise in the power loop.  It is a good introduction to the topic and was written by a very experienced and knowledgeable member of this forum, Grumpy_Mike.  His site also has some useful information on various other topics as well.