Schematic Help! (I'm a NOOB)

Just to preface - I am a bit of a noob when it comes to creating circuits so some of my questions may be a bit basic for some of you gurus and engineers out there. If you could bear with me and help me out, i'd be forever in your debt!

So I just wanted to see if anyone here could help make sense of this schematic. It is for an interactive bluetooth coffee table actually which is hosted on instructables (here is a link: http://www.instructables.com/id/Dot-an-Interactive-Coffee-Table/)

here is the schematic:

I have tried to create this circuit and I am unable to get any power to my Arduino Mega. This circuit should connect the HC-05 Bluetooth unit to the Arduino, and connect the LED strips (WS2811) to power source and Arduino to run sketches & games. According to the schematic, it seems like they want the Arduino powered through the 5V pin, which brings me to my opening question -

  1. When I plug my Arduino Mega in via USB, I see the two lights on the board come on (one orange one green). This schematic shows the 5V Pin and Ground connected to the power supply. Should I use the 5V pin according to the schematic? From what I've read here so far, people seem to think using the 5V pin to power the Arduino is more problematic than using the Vin pin. I am trying to use a switching power supply to power the board via the Vin pin. When using the Vin pin, if connected correctly - the same two lights should come on, correct?

This power supply has the same connections as mine which are:

L, N, (Ground), V+, V-

According to the Schematic above, which of the orange power connections (for the LED strip and the Arduino board) should go into which ports on the Power supply?

Also, any notes on the voltage that should go into which pins on the board? hope this all makes sense, if anyone needs clarification - please let me know! :slight_smile:

V+ and V- are the output of the supply, so V- -> GND and V+ -> 5V (if its a 5V supply).

You must mains-earth a supply like this, don't omit that, and I'd ground V- too - ie you can
strap earth, V- together.

It is very bad to apply power to the 5V pin and plug in USB at the same time. This causes power to be back fed into the USB and can damage it.

Here's Big Clive explaining the issue, and also tearing down a powered USB hub that was stupidly designed with this flaw.

The VIN pin has circuitry connected to it that will block the USB power if you are applying power to it or the barrel connector, but the 5V pin does not have any such protection.

Do you have any experience working with mains voltage? The power supply in your picture requires directly wiring mains voltage to exposed screw terminals. I do not have any confidence that you are competent enough to do this without hurting yourself. Do not use that power supply.

Get a 9V wall wart to power the Mega, and use a buck converter module to step it down to 5V for the LED strips.

Jiggy-Ninja:
It is very bad to apply power to the 5V pin and plug in USB at the same time. This causes power to be back fed into the USB and can damage it.

Here's Big Clive explaining the issue, and also tearing down a powered USB hub that was stupidly designed with this flaw.

The VIN pin has circuitry connected to it that will block the USB power if you are applying power to it or the barrel connector, but the 5V pin does not have any such protection.

Do you have any experience working with mains voltage? The power supply in your picture requires directly wiring mains voltage to exposed screw terminals. I do not have any confidence that you are competent enough to do this without hurting yourself. Do not use that power supply.

Get a 9V wall wart to power the Mega, and use a buck converter module to step it down to 5V for the LED strips.

I have already connected the power supply by stripping a PC power cord and connecting to the power supply. Despite my noob-ness I have made power supply connections before. Currently I have power to the supply unit fine (LED is illuminated), just not powering the Arduino. I was thinking of using a wall wart but that still doesn't address how I'd power the LED strip though - wouldn't I have to still get a switching power supply for that?

MarkT:
V+ and V- are the output of the supply, so V- -> GND and V+ -> 5V (if its a 5V supply).

You must mains-earth a supply like this, don't omit that, and I'd ground V- too - ie you can
strap earth, V- together.

I have heard that about connecting Earth and V-, I will do that for sure. And when you say earth - mains, are you saying to also connect V+ and earth as well? Also, I am not confident this is a 5V supply - I am going to get a Multimeter today to test before powering on the unit. But in the case this unit outputs 9-12v, should I use the VIN pin instead or should I adjust the V Adj til I reach 5V? Is running current into 5V Pin on Arduino more dangerous to destroy my Mega than the VIN pin? Thanks!

puredark:
I have already connected the power supply by stripping a PC power cord and connecting to the power supply. Despite my noob-ness I have made power supply connections before. Currently I have power to the supply unit fine (LED is illuminated), just not powering the Arduino. I was thinking of using a wall wart but that still doesn't address how I'd power the LED strip though - wouldn't I have to still get a switching power supply for that?

Correct, you aren't going to power LED strips with the puny linear regulator that's used on Arduino boards. You can use multiple power supplies to power different parts of your circuit depending on convenience or requirements. A wall wart for the Arduino and the beefy SMPS for the LED strip works fine.

puredark:
I have heard that about connecting Earth and V-, I will do that for sure. And when you say earth - mains, are you saying to also connect V+ and earth as well? Also, I am not confident this is a 5V supply - I am going to get a Multimeter today to test before powering on the unit. But in the case this unit outputs 9-12v, should I use the VIN pin instead or should I adjust the V Adj til I reach 5V? Is running current into 5V Pin on Arduino more dangerous to destroy my Mega than the VIN pin? Thanks!

I recommend not connect mains earth to either of the outputs. There's no need to, unless the thing you are powering needs to be mains earth referenced for safety or EMI reasons. It is unlikely that LED strips will need to be mains earth referenced.

It depends very much on your power supply. Many different ones are made with the same standard case like that. The one you pictured does not have a fixed output and is adjustable.

It is not dangerous to your Mega to feed 5V into 5V pin as long as the supply is properly regulated. You would need to take great care that the adjustment pot does not move after it is set. It is dangerous to your computer's USB port, due to back feeding that I already mentioned. Cheap USB ports that skimp on protection circuitry can actually be destroyed when back fed with power.

Jiggy-Ninja:
I recommend not connect mains earth to either of the outputs. There's no need to, unless the thing you are powering needs to be mains earth referenced for safety or EMI reasons. It is unlikely that LED strips will need to be mains earth referenced.

It depends very much on your power supply. Many different ones are made with the same standard case like that. The one you pictured does not have a fixed output and is adjustable.

It is not dangerous to your Mega to feed 5V into 5V pin as long as the supply is properly regulated. You would need to take great care that the adjustment pot does not move after it is set. It is dangerous to your computer's USB port, due to back feeding that I already mentioned. Cheap USB ports that skimp on protection circuitry can actually be destroyed when back fed with power.

Nice - so if I'm going to update sketches on Arduino and I am using the 5V input pin, I should unplug the power source before plugging in the computer via USB to be safe?

"Also, I am not confident this is a 5V supply "
Good call. Isn't there a label on the side of the supply as well?

puredark:
Nice - so if I'm going to update sketches on Arduino and I am using the 5V input pin, I should unplug the power source before plugging in the computer via USB to be safe?

Yes.

If you insist on that sort of scheme, I recommend chopping a USB cable in half and connecting that to the 5V power supply to power the Arduino through the USB port. This way, you are forced to unplug the external power supply before you can plug in the computer. Even if you think you know what you're doing now, if you decide to do some modifications 6 months in the future you'll be grateful for the idiot-proofing.

My Lenovo didn't like it when I applied 5V to the power header with USB connected, it complained about a power surge and shut down the port. I had to restart the PC to reset the port.
I was connecting with an FTDI Basic, so I made a short extension cable with a connector in the 5V line so I could power the board and not have USB 5V connected.

CrossRoads:
"Also, I am not confident this is a 5V supply "
Good call. Isn't there a label on the side of the supply as well?

Yes - it actually says DC Output: 12V 2A & AC Input: 110/220V + 15%

so its 12V supply. I imagine it would run slightly lower but I will use a multimeter to ensure the output is adjusted to 5V. Thanks!

puredark:
I have heard that about connecting Earth and V-, I will do that for sure. And when you say earth - mains, are you saying to also connect V+ and earth as well?

NO, certainly not! That would short out the supply!

Also, I am not confident this is a 5V supply - I am going to get a Multimeter today to test before powering on the unit. But in the case this unit outputs 9-12v, should I use the VIN pin instead or should I adjust the V Adj til I reach 5V? Is running current into 5V Pin on Arduino more dangerous to destroy my Mega than the VIN pin? Thanks!

If its 9V or 12V you won't be able to adjust it to 5V, the adjustment range is small, but yes, power Vin, and you'll need a supplementary 5V regulator for the LED strip as they can take a lot of current.

MarkT:
NO, certainly not! That would short out the supply!If its 9V or 12V you won't be able to adjust it to 5V, the adjustment range is small, but yes, power Vin, and you'll need a supplementary 5V regulator for the LED strip as they can take a lot of current.

So something like this:

placed between the LEDs to the power supply?

No. A linear regulator is going to get literally roasted trying to run LED strips. You need a buck converter module.

Okay - I plugged it in as is and the lights are not turning on at all. I will get one of those and try it out. I hope I didn't destroy my led strip because I had the power source plugged in to the LED connector (as in the schematic) but my LED Strip had an extra red and white wire (not on the interlocking connector) and it was inadvertently touched to the V+ connection as well. A small spark occurred. Did I burn all 196 lights on my LED strip? Just throwing that out there too

Sparks are generally bad. I think it's more likely you popped a fuse in the power supply by shorting it out than destroying the LEDs. Does the power supply advertise an overload/overcurrent/short circuit protection?

I don't believe there is short circuit protection but the power supply still turns on and sends power to the Arduino even after the spark incident. Just no lights turn on. When you load a sketch onto the Arduino it should automatically play when the Arduino gets powered on correct?

Hi,
Can you please post a complete copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Include your power supply connections.

Can you please post a picture of your project so we can see your component layout?

Thanks.. Tom.. :slight_smile:

TomGeorge:
Hi,
Can you please post a complete copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Include your power supply connections.

Can you please post a picture of your project so we can see your component layout?

Thanks.. Tom.. :slight_smile:

Is this what you were referring to?