At the moment I am working on making a simple text editor using an Uno, SD shield, 16x2 LCD, and a PS/2 keyboard. I've been able to print characters to the LCD from the keyboard fine, but I'm worried I'll destroy my Arduino.
I'm not very knowledgeable about hardware yet, but from what I've read, the max safe output current of an Uno is 200mA. The keyboard I have says 100mA on the back, but I'm not sure how much current the LCD nor SD shield use. I've only run it for a couple minutes total, so nothing's been destroyed (yet), but I'm fairly certain if I use it much longer, something will get destroyed... And probably the worst part is I'm not using any resistors... So yeah, I won't use it anymore until I can get some input.
Maybe I'm trying to get my little Uno to do too much with this?
the first thing to do is...... to post your schematics (and I mean yours, not a "I've wired it like in this video/page .....")
with all the needed infos. (pins numbers, voltage, etc..... )
give as much useful information as you can.
OK, I can do that later. I need to get some sleep, but after that I’ll post a Fritzing schematic of everything I’m using.
How are you powering it? Through the Arduino's power connector?
If so, there's a very simple test called "put your finger on the regulator".
If it's burning hot: bad.
If it's not: OK
If you're powering it any other way then the limit is the external power supply, not the Arduino.
Arduino Uno regulator is good for 800mA depending on high the incoming voltage is.
7.5V is much more likely to yield 800mA vs 12V as the regulator dissipates the higher voltage as heat.
Also: don't confuse the current limit of the Atmega328P, which is 200mA for the DIP package due to having only 1 Vcc pin, vs the 5V regulator current limit (800mA, input voltage dependent), vs the USB supply limit of 500mA.
And… for future reference, if you aren’t sure of component ratings, you should not power them up before investigating further. A couple of seconds may suffice to damage a part.
I am powering everything on the breadboard by the Arduino's 5v pin.
A couple clarifications before the schematic are needed though, since Fritzing doesn't have everything I used. This is the actual SD Shield I used. I'll be using a microSDHC card with it. This is the LCD and potentiometer I used. The resistor seen in the schematic is 1k ohm and is only for limiting the backlight, since the full amount is too bright for me. The pin on the LCD where the resistor and power are isn't even connected, so there's no issue of side effects. The wires going off the left side are as follows:
Red - data
Gray - ground
Yellow - clock
Brown - power
EDIT: I guess the image is too large for the forum to show, so you'll have to visit the Photobucket link:
@Polymorph: Yeah, that's a good idea. I'll keep that in mind.
Thanks everyone for the help!
I would prefer a schematic. Much clearer.
You asked for it...
The first picture seems much easier to look at, but maybe I'm not used to schematics.
If your "yikes" is n response to the schematic being hideous, then blame Fritzing. I made the breadboard image by hand; it generated the schematic. I do much better with actually seeing what's going on then trying to read a "code" and decrypt it at the same time, so I went with the visual representation. If you've ever owned an Arduino I don't see why you need the schematic to tell what's going on - it doesn't give any more information here than the first image does.
If it only takes a couple seconds to destroy anything, and I ran it fine for a few minutes, it must be fine. The lack of response to my original question tells me there is nothing to worry about here.
No, I said it may take only a few seconds to -damage- something.
Did you take a look at the links? As for the schematics, any schematic program requires you to move the wires and components around to make a clearer representation of the circuit.
I'm only suggesting. There are very good reasons why we use schematics and not pictorial diagrams.
What are those reasons?
I'm concerned much more with function than aesthetic, and for me pictorial diagrams are a lot easier to understand. Sure, with schematics you can include necessary information of components more easily, but that's nothing some labeling or a list can't fix with a diagram.
Anyway, if there's any missing information that anyone needs to help me, I'll be glad to provide it. If I want to learn how to make schematics, I'll do so on my own, and create a thread for that if I needed to. Right now I'm concerned with things not blowing up or burning out, not how to represent those things in a picture.
I’ll test that soon. Correct me if I’m wrong, but I just realized that the peripherals I’m using will draw their current from the power directly, so the limit would be 800mA and not 200mA. I think I was confusing the power draw on these devices with the draw from the Arduino’s digital pins, so I should be well below 800mA.
Crossroads covered that in reply #4.
He explained the difference, but didn’t explicitly state what is drawing power from where. Sorry, I’ll keep working on my mind-reading abilities.
EDIT: Well, I ran the sketch with everything plugged in, and it didn’t overheat, so I guess I’m good. Thanks for the help everyone.
I'll test that soon. Correct me if I'm wrong, but I just realized that the peripherals I'm using will draw their current from the power directly, so the limit would be 800mA and not 200mA. I think I was confusing the power draw on these devices with the draw from the Arduino's digital pins, so I should be well below 800mA.
no and yes but...:
no, on your fritzing diagram, I see you powered the breadboard from the 5V pin of arduino, which outputs a regulated 5V from the regulator on the board .
yes but...... it depends on the power supply : if you power arduino from 12V, then I'm afraid the power dissipated in the 5V reg. will be far too high !
By "power directly" I meant from the 5v pin rather than through the ATMega328. And I power my Uno by USB from my laptop, so that shouldn't be a problem.
In the first post of this thread I had no idea that only the microcontroller was 200mA, and the power itself is 800mA max, so that's where my worry was.