double psu distribution(5v, +12v, -12v)

Hi. I have a project that uses multiple power supplies. The arduino part is all 5v, there are 3 arduino in total(1 mega, 2 atmega328) and another part with operationals.
The arduino mega has 4067 and max7221 connected to it along with potentiometers, switches, leds… then through i2c connects to an atmega328 which drives two 40x2 lcd displays with backlight(each one draws 30mA according to datasheet… seems low) and a 16x2 display 100mA… Then the second atmega328 has some DACs connected to it, and after this some operationals(+12v, -12v).

I thought several ways, i want the arduino mega to draw the less current possible, because with 12v at it’s input, the regulator will get hot without heatsink, so i won’t connect the backlights to that part.

So i thought instead of feeding 12v to each microcontoller’s regulators, to use an external 5v supply. The supply uses 7812, 7912 and 7805, with 0.75A theorical at each line, I thought I could connect it like this:
(drawing)

Looks fine?

Diagram1.png

You refer to -12v and 7912. How do you plan to get the -Ve voltage?

What type of power supply are you going use for 5v? You may simply be able to use a regulator to bring the 12v down to 7.5v or so to feed to the input jack. This may be more space efficient and the heat is moved from the onboard regulator to an external regulator.

Weedpharma

A 5v switching regulator can give you good clean 5v from 12v in, without heating up and wasting power. Pololu has a great range of them. I've bought nearly every single type they make with 5v output.

I will have to bring my linear last century brain into the current switch mode century!

Weedpharma

This is the supply http://www.nutsvolts.com/uploads/magazine_downloads/11/January%201998%20Thomas%20Henry%20-%20Power%20Supplies%20for%20Electronic%20Music.pdf

I've never dealt with switching regulators, and I don't know if there is a wide range of types here in Argentina.

@weedpharma So you say to bring down to 7.5v, and that goes to arduino mega regulator, what about the others atmega328? Should I use the same 5v line from the arduino mega? Or more like this? :

7.5v > Arduino mega reg
7.5v > atmega328 7805
7.5v > the other atmega328 7805

OR

7.5v > arduino mega reg > 5v from mega to the rest of the circuit

after this some operationals

I don't know if it matters to you but I have never seen op amps referred to as
"operationals". Most people would say:

after this some op amps

also, not to be picky but this:

7.5v > Arduino mega reg
7.5v > atmega328 7805
7.5v > the other atmega328 7805

I would express as:

7.5v > Arduino mega Ext. dc Barreljack
7.5v > 7805_1 => atmega328
7.5v > 7805_2 => the other atmega328

Why do you need bipolar op amps ?

there are 3 arduino in total
(1 mega, 2 atmega328)

Do you mean Arduinos or do you mean standalone ATmega328 chips ?
If you mean Arduino products when you say "2 atmega328" do you mean UNOs ?
If not, which arduinos do you mean ? (that have ATmega328s)

If you use a switchmode regulator, you can bring the 12 volts down to 5v and feed it to the 5v on all of the boards.

The switchmode is far more efficient than the linear regulators such as 7805. They are very common on eBay and only cost a few dollars each.

This arrangement means you do not need two mains powered supplies, just the 12v that is then dropped to 5v.

Weedpharma

raschemmel:
I don't know if it matters to you but I have never seen op amps referred to as
"operationals". Most people would say:

Why do you need bipolar op amps ?

Do you mean Arduinos or do you mean standalone ATmega328 chips ?
If you mean Arduino products when you say "2 atmega328" do you mean UNOs ?
If not, which arduinos do you mean ? (that have ATmega328s)

In spanish we say "operacionales", so sometimes I forget to say "op amp" in english

Now that I think about it, I think I don't need a bipolar supply. In the original design I needed some digital outputs to be -10v - 10v. But not anymore. And apart from that, at the output of the DACs(MCP4922) I use op amps for buffer and amplify/atenuate a little(the outputs controls analog synthesizers, and the gain is minimum, to compensate possible scaling errors depending on the synthesizer)
I need the op amps to be able to output in the mV range. I suppose I could just make a virtual ground to be able to output close to 0v.

When I say atmega328 I mean standalone.

I'll see what switching regulators I can get around here @weedpharma

thanks

I don't know what single-supply op amps are available in Argentina but the LT1215 is an example of an op amp specifically designed for operation with 5V circuits.