Easily powering multiple devices from 5V...

I posted this same question in the "installation & troubleshooting" section, but received nothing in the way of a response...

The question/concern I have is regarding powering 10 DS18B20 temperature probes (Or anything at all) while I have a 3.2" TFT LCD Touchscreen shield installed on a Mega 2560.

Basically the TFT uses the 5V pin, but it does not provide any kind of pass through to allow for powering other devices, which seems to be a huge oversight to me, since generally speaking, you would surely have more than just a display if you are using a display... Hope that made sense...

Anyhow, right now my solution involved cutting the end off and stripping one of my jumper wires, pushing it down into the 5v header, then installing the display shield... Which is not even remotely ideal to me, not to mention how unprofessional it looks... Given that I am hoping to sell some of these temperature displays/graphs to computer enthusiasts, I need them be semi/professional in appearance.

Any help with this would be greatly appreciated! Thank you in advance, and for all the help these forums have provided me!!!

Thank you,

~J

Yes, silly oversight. You can power devices up to 20 mA or so from a port pin set to output HIGH. The DS18B20 requires up to 1.5 mA while converting the temperature, so all 10 could easily be powered from one pin. You should add a ~ 10 to 100 nF capacitor from the power pin to ground, to lower the noise levels.

How did I miss that??? It never occurred to me that I could sap power from a data pin set to high… Thank you for the elegant, and very simple solution…

~J

Likewise, you can usually use an output pin set to LOW as ground, but again, only up to about 20 mA.

Forgive my naivete, but I have never had to purchase caps before, as this is my first Arduino project, where can I pick up the appropriate capacity and voltage capacitors for such a use?

~J

If you live in the U.S., there is usually a Radio Shack nearby. But you may not need the cap, so try it without.

Radio shacks are closing down, so I am not sure if the one near me is open or not... Will try... Any specific voltage/specs beyond the capacity I should look for?

Working voltage 5 or higher.

Please forgive my lack of knowledge, I am pretty resourceful most of the time, and I search for information thoroughly before asking questions (pride and the like), but alas, I am unable to find sufficient information regarding caps, you mentioned, "working voltage 5 or higher", I am finding a lot of 50v caps within the range I am looking for, and given my lack of knowledge, I can only assume that such voltage is far too high and would do damage...

How high is safe in this situation?

Again, I am terribly sorry, I am very good when it comes to basic electronics, but I have never had to use caps before (Other than replacing the odd popped cap on a motherboard or other device, but when it comes to choosing one to implement for a project, I am unfamiliar... Additionally if someone could point me to a reliable reference for learning about caps, I would be very grateful! If not, I can surely find some resources in sort order...

Thank you,

~J

What is it about the "or higher" that you are having difficulty with? A capacitor that can withstand 50V is not going to be damaged with 5V on it. The only down side is that it will be physically larger than it could otherwise be.

The whole tone of this thread is screwey anyway. You simply have a wiring problem and not much of one at that. Simple wire up all your devices to the same Pins. Don't piss about using output pins to power stuff.

You might need to use strip board to wire to. Do not push wires in the sockets use a proper header strip and solder your wires to that.

I stated VERY clearly that I am not experienced with capacitors, with that in mind, I do not know if the 50V is the output voltage from the Capacitor. Thusly, if the 50v is the output, then there I would be with a pile of smoking electronics, which, just to be clear, is NOT my goal... That was meant as a joke, just trying to lighten things up... :-)

I also specifically asked if someone were able to post some resources for learning about capacitors, since it is something I know VERY little about, which I hoped would allude to that fact.

You say to wire everything to the same pins, please forgive me, but I will restate the problem, the only 5v supply on my 2560 is occupied by the 3.2" touchscreen LCD shield, and there is no pass through header for me to tap into, which is why I am asking in the first place...

Is your suggestion to desolder the existing headers on the shield and replace them with pass through headers? I have no problem with that, I just figured someone would have a simpler solution.

I do appreciate your time and effort in assisting those of us that are new and excited to learn more about Arduino, and electronics in general!

Thank you kindly,

~Jacob

OK so it is working voltage you are having trouble with.

This is the maximum voltage the capacitor will work with before it gets damaged. A capacitor is a passive device, it stores electricity a bit like a battery. It only stores the voltage you put into it. So if you only ever put 5V into it then it will only have 5V in it. You can put any voltage into it up to the maximum working voltage. There is no way that a capacitor will give you more, therefore there is no way a capacitor can cause anything to cause anything to burn up.

The amount of electricity a capacitor can store is normally very small, the proper name for this electricity is charge. Its main use is to smooth out a voltage that changes with time. On all power supplies their are tiny changes in voltage called noise. A capacitor will reduce that noise. Too much noise will stop a device from working.

Capacitors have other applications but basically they all involve slowing down changes in voltage.

As to the 5V situation if it were me I would solder a wire on to a 5V point on the shield, the same for the ground.

This might be a bit advanced for you at the moment but have a look at my pages:-

http://www.thebox.myzen.co.uk/Tutorial/Introduction.html

http://www.thebox.myzen.co.uk/Workshop/Introduction.html

And for examples of what you can build when you know stuff see:- http://www.thebox.myzen.co.uk/Hardware/Projects.html