Hi - I have a device with the following components:
-Arduino Nano (USB connection only)
-GPRS Shield (SIM900)
-2x16char 16pin LCD
-PIR motion sensor
So, everything is functional right now - I have the SIM900 plugged into the wall with an adapter and the Nano powers everything else via USB.
There are 2 issues:
- I want to get the whole system on one wall adaptor.
- As it is right now, it seems the power is a little low - every time an LED blinks, the LCD screen dies down a bit.
I have some 5v regulators, I'm wondering if I should just stick that in front of the LCD? I also need to join the Nano and the SIM900 onto the same power source...I think I can run some wires from the Nano to the SIM900, but I worry that there's already not enough power coming from the Nano and the SIM900 is picky about that..
Any help here would be very appreciated - I have no electrical engineering background and I've never had to scale up or down power before.
Check the rated current of the DC voltage supply --- usually written on the sticker or the supply --- somewhere. It's kind of a recommended value of current that the supply should not exceed.
So --- depending on how much maximum levels of current is being used, the power supply should be chosen to handle that maximum level of current comfortably.
Also - estimate the current through the LEDs when they are turned on. This will often depend on the resistance that is series with the LED (and the supply voltage, and the voltage drop of the LED). We can assume if the LEDs are working just fine right now.
Also ----- considerations should be made about what is powering what. The LCD is being powered by the DC voltage supply too, right? This is where a drawing of the system - showing connections - can be handy.
I'm new to Arduino, I kind of just made it up as I went along, not much planning.
Here's a picture of this mess:
I wish I could take power from the SIM900 shield's DC adaptor and use it to power the adaptor too...right now I'm using USB power as well.
I can't even figure out how to power the SIM900 with the arduino either 
edit: All the components (not SIM900) are being powered by the Nano's 5v pin attached to the breadboard hot rail, EXCEPT the two LEDs, which are each powered by digital pins.
I can't even figure out how to power the SIM900 with the arduino either
You can't. It draws over an Ampere when transmitting. The Arduino can't handle more than a few LEDs.
Your external power adapter should be rated for 2 A or so.
jremington:
You can't. It draws over an Ampere when transmitting. The Arduino can't handle more than a few LEDs.
Your external power adapter should be rated for 2 A or so.
Alright so if I wanted to switch to a single DC power source, it would have to be something like 12-14v & 2A ? Would that be damaging for the nano to connect to a higher amperage power source? can that signal be changed before going to the nano?
Sorry i'm not very good at electrical stuff 
jtbennett:
Would that be damaging for the nano to connect to a higher amperage power source?
Short answer, No. Amperage (Amps) are load dependent. If you have a water hose with a sprayer on the end, then however hard you squeeze the handle is however much water comes out. If you only squeeze it a little, then water drips out even though the whole hose is full of water and has the capability to spray more.
jtbennett:
Can that signal be changed before going to the nano?
By "signal," do you mean voltage?
jtbennett:
Sorry i'm not very good at electrical stuff 
Gotta learn somehow
JT..... a regulated voltage source will automatically attempt to keep the voltage at the desired regulated value.... such as 5 volt DC. The rated current will be a value of current written usually somewhere on the supply casing..... eg. 2 ampere. So the maximum power output will approximately be the product of the regulated voltage and the rated current... p = I V .... 5 x 2 = 20 watt.
Just got to make sure the device to be powered gets the correct supply voltage.
Also...if the regulator supply can't supply the quantity of current to be used by the load.... then the voltage supply probably won't operate in the normal way.... so could lead to problems like circuit not functioning properly.
Thank you to both of you - I'm gonna do some reading and come back to your answers so I can make more sense of it. I only just made an image of the circuit, figured I should post it even though it doesn't seem to be needed anymore:
there seems to be 2 definitions of "Ampere": that used by the rest of the world, and Asian amps. on a side note, in a similar vein: don't buy shoes made overseas in the same size as Red Wings. try them on to determine their real size.
a power supply made in the USA that claims to produce 2 amps will be half the size of a SATA drive, weigh enough to hurt if dropped on a bare foot, and will have a 5mm diameter DC power cord.
a bogus power supply claiming to produce 2 amps will be the size of an ice cube and have an angel hair pasta sized DC power cord.
Would that be damaging for the nano to connect to a higher amperage power source?
you give it the right voltage, and it takes the amps it needs. the ability to draw more amps will not make it draw more amps.
Well it seems to me I just need to calculate the sum of the voltages for the components and pick a power source that hits that voltage, as well as meets or exceeds the amperage requirements of the component with the highest needs....is that a safe way to do it?
I decided to remove the SIM900 and put a WeMos D1 (less of a power hog) on there so I can control it with Blynk. I got the D1 working with Blynk, but it does not recognize my code that was running fine on the Nano (same exact pinout too).
So...I'm back to square one again here, I'll have to come back to power later :\
jtbennett:
Well it seems to me I just need to calculate the sum of the voltages for the components and pick a power source that hits that voltage, as well as meets or exceeds the amperage requirements of the component with the highest needs....is that a safe way to do it?
Not like that jt.
It's not done like that. Each device module ... eg LCD, your sim module etc has a required supply voltage.
When we're lucky --- most of the modules might run off say 5 volt DC. This is when we can use a 5 volt regulated voltage supply. And that voltage supply needs to be able to supply the amount of POWER that all these devices or modules require. This is assuming there are no devices that abruptly require relatively high current every once in a while --- like relay coils to be powered --- in which case it is often desirable to have a separate dedicated voltage supply (power supply) for those sorts of devices.
If you have 1 module that requires a different supply voltage --- such as requiring 12 V DC when compared with other modules requiring 5 V DC, then it will be necessary to either have two different power supplies --- one 12 V one, and one 5 V one. Sometimes, people might use the 12 V one in order to produce a 5 V one --- which still results in 2 separate voltage supplies.
And then you need to make sure that the maximum (expected/predicted) current being drawn from each supply doesn't exceed the rated current of the voltage supply. And the rated current is the specified current (from manufacturer) that shouldn't be exceeded. So if your 5V supply is supplying some circuits that require 5V (supply), and if 1 circuit will draw at most 0.5 ampere, and the other circuit draws at most 1 ampere ...... then the total current that might be drawn from the power supply might be at most 1.5 ampere. So...... the power supply needs to be chosen to have a maximum output current more than 1.5 ampere ....preferably higher .... like 2 ampere or even 2.5 ampere or more. Usually, the power supply should be expected to operate happily at the rated current. So a 5V, 1.5 ampere DC voltage supply should work. But it's often better to choose one that has a more substantial output power. This just means ... choose components that can handle the conditions comfortably.
And - one formula to remember for power in DC circuits is ..... product of voltage and current .... P = V.I .... for DC voltages and currents.
If the SIM900 and the other devices can all be powered by 5V, then a shared 5V 2 to 3 Ampere power supply is probably all you need for the system.
You can power the Arduino via the 5V pin, rather than going through the RAW, Vin or barrel jack connections.
Don't bother with Fritzing diagrams, they waste everyone's time. Pencil and paper is fine.