Did two voltages smoke my board? Or was it the pull down resistor?

BACKGROUND:
Here is my reasoning for the attached circuit (not really a schematic, more of a connection diagram). I am powering an Amazon Echo Dot in addition to some fancy lights inside of a pretty enclosure. Because the power needed by the Echo is 12VDC and the Arduino Nano is 5VDC, I figured the 12V power supply could do the trick for both. Because 12V is the highest unregulated power the Nano can handle I didn't want to push that limit and heat up the board, so I opted for a 5VDC 7805 regulator and I put that into the 5V pin. I did the same thing on a recent project and I noticed an issue when the board was powered AND the USB was connected. For the most part I got it working like that and after debug, I never used the USB again. Usually I unplug the 12V when I upload a sketch.

I wanted to save the settings for the LEDs in memory so it would come up the same after having the power cycled. So I added the momentary switch (close to dead center of the diagram SW1). I like the switch for three reasons. 1. I had one. 2. It is small and will be easy to mount. 3. It seems pretty robust. What I don't like about it, is it is normally closed. But I figured that wasn't a problem for the Nano. So I added the switch without the resistor R1. It didn't work. When I monitored pin D4 in the serial monitor, I saw that it was indeed HIGH, but when I pressed it, it stayed high occasionally going low in a more or less random fashion. I figured it was floating and I needed a pull-down resistor. So I added R1, which is 12K. I plugged in the 12V, then I plugged in the USB so I could use the serial monitor and I smoked the board. The component that burned was the diode on the underside of the board that attaches to the USB connector.

I figured I must have gotten a solder short on the board, but NOPE. So I looked up pull-down resistors since I just used a 12K because I had used one earlier as a pull-up. Pull-up, pull-down, what's the diff, right? Well online for OTHER circuits I found there IS a big difference, but on these forums and other Arduino related sites, it seems like people use 10K resistors all the time. So 12K seemed like it should be fine.

QUESTIONS:

  1. Is it better to use a regulated 5V DC supply to pin 5V to power a Nano if you need two voltages, or should I have used 12V into the Vin pin?
  2. Are the 5V supply and the 5V supplied by the USB competing in a bad way?
  3. If so how do I stop that?
  4. Is the 12K value for the pull-down ok?
  5. What's the average flight speed of a swallow?

I have another board, but because I can't find anything I did wrong on the first one, I don't have a corrective action and I'm afraid that means I will just smoke the second board too.

Oh, and I did change out USB cables in case that was the cause. I don't know if it's important, but the USB ports on my laptop wouldn't work after this. Fortunately, they came back to life after a reboot.

Thank you.

  1. 5 Volt DC is prefered.
  2. Don't apply both USB 5 volt and 5 volt to the 5 volt pin.
  3. Read (2). Just don't do it.
  4. 12k is OK.
  5. Check up swallows on Google, Wikipedia.

Railroader:

  1. 5 Volt DC is prefered.
  2. Don't apply both USB 5 volt and 5 volt to the 5 volt pin.
  3. Read (2). Just don't do it.
  4. 12k is OK.
  5. Check up swallows on Google, Wikipedia.

Ok, follow up question. How do you apply power AND use the Serial Monitor? The USB has to be plugged in to monitor it, but I can't always power other devices from the Nano. In this case, I suspected dirty power from the adapter was causing a software variable to be out-of-range. It isn't out of range with just the USB. I wanted to check if my filtering on the power supply worked.
Also, I'm sorry to inform you your answer to number 5 is incorrect.

Hi,

Have you got a DMM to measure your circuit voltages?

Sorry but, can I suggest you DRAW with pen(cil) and paper your circuit and post an image.
Forcing CAD apps that are not designed to do schematics is not good.

You can do better than that when you draw and keep the multiple crossing of wires to a minimum.
As you are in troubleshooting mode, a good schematic will help immensely, in fact reverse engineer your project to obtain your new circuit, it may help.

Tom… :slight_smile:

"5. What's the average flight speed of a swallow?"
African or European?
Is it carrying a coconut?

Um, the Echo Dot is a 5V device.

Hi,

Get yourself a USB cable.
Cut the cable in half.
Reconnect ALL the wires in the cable EXCEPT the RED wire which should be +5V
Now you have a powerless USB cable to communicate and program an external powered Arduino controller.
This is mine, the terminals on the top are connected to the two disconnected ends, so I can still make it a power through and/or insert an Ammeter to measure current.

Tom... :slight_smile:

Think I would put more capacitance on the regulator, input AND output. Could have went into oscillation and put x volts on the 5V pin?

Hi,
What is the 12V supply?
I agree with @JCA34F, you need a bit more than 0.33uF on the input side of the LM7805.

Tom.... :slight_smile:

Railroader:

  1. 5 Volt DC is preferred.

Definitely! Do not use a 7805 or similar series regulator, especially if you are powering something other than the Arduino.

Get a switchmode "buck" regulator rated well beyond the current you expect to require. You show a WS2812 strip but fail to explain how many LEDs you propose to use. Allow 60 mA per LED.

Railroader:
2) Don't apply both USB 5 volt and 5 volt to the 5 volt pin.
3) Read (2). Just don't do it.

Wrong! :roll_eyes:

You failed to notice, this is a Nano, not a UNO!

Point is, you will need to disconnect the "5V" pin whilst programming unless your main 5 V supply is live.

Railroader:
4) 12k is OK.

It is, but don't use a pull-down. Connect the switch from the pin to ground and use pinMode of INPUT_PULLUP. You do not need another pull-up as long as the switch is close to the Arduino, is of good quality and not wet. A 12k pull-up is fine.

Railroader:
5) Check up swallows on Google, Wikipedia.

Or try a different porn site. :sunglasses:

OP:

  • If the potentiometers are not connected to ground, I can't see how they would work.
  • What do you mean by your board being "smoked"? You have not explained.
  • Is this a Nano or a clone? Please cite the source so we can figure it out.
  • If you caused the Laptop USB ports to shut down, you must have connected something badly wrong, nothing to do with pull-down resistors.

TomGeorge:
Get yourself a USB cable.
Cut the cable in half.
Reconnect ALL the wires in the cable EXCEPT the RED wire which should be +5V
Now you have a powerless USB cable to communicate and program an external powered Arduino controller.
This is mine, the terminals on the top are connected to the two disconnected ends, so I can still make it a power through and/or insert an Ammeter to measure current.

Not relevant to a Nano. other than to measure current. :astonished:

Hi,
I think the BLACK dot on the pot and resistor circuit leads represents gnd.

Tom... :slight_smile:

Presumably it must. Not a bad convention really, but not common practice. :grinning:

CrossRoads:
"5. What's the average flight speed of a swallow?"
African or European?
Is it carrying a coconut?

We have a winner!

I'm still subject to the ridiculous 100 post limit (MHO), so I will respond to all of you in order in one post:

TomGeorge,
Yes, I have a DMM and I apologize for the "schematic." This is the kind of thing I do when I'm building, to give myself an idea of how to lay things out. I prefer not to make a true schematic until I'm nearly done, that way I kind of know how to make it less cluttered. There will probably be more features coming to this device.

CrossRoads,
Well done!

SteveMann,
Re: "Echo dot 5V device." Well I'm not sure why it says "input 12V DC and 1.25 A" on the bottom or why it came with a 12V power supply. This is an Echo Dot 3. Should I be contacting Amazon?

TomGeorge again,
Re: "Cutting power out of a USB cable." That is friggin' awesome. I totally could have come up with that if I weren't so stupid. I also like the added terminals. Nice touch. This is pretty much what I was looking for.

JCA34F and TomGeorge,
Re: "What PS am I using?" Originally I was planning to use the power supply that came with the Echo, but I added a servo motor as an indicator to which mode the device was set. When I did this, it exceeded the maximum current of that supply. I looked into servos that drew less current, but when I considered the maximum possible current draw with, lights, music, servo and whatever else Alexa needed (I measured MUCH less than 1.25A for the dot, even with the volume up so I don't know why it's spec'd so high), I decided to go with a different supply that was capable of something like 4A. Plenty of overhead. It had the additional feature of a plug on a wire that goes to the wall instead of a albeit small wall wart. This is intended as a gift to some friends that live in the UK. This would allow them to put a simple adapter on the plug and still use it, unlike the wall wart. In Germany the outlets are recessed so those wall warts don't work. I can't remember if they are in the UK or not, but either way this will work. That supply turned out to be problematic. After the servo moved to an indicated position, it kept moving around and I think the LEDs were flickering a little. When I looked at the serial monitor I saw that the value of the resistance from that resistor pack in the schematic was going out of range. I thought this was odd because I got that range by measureing it with my desktop power supply. So I switched back and it was solid. So I looked for another one online and found this one, which said "no noise." Gotta love that optimism. Amazon.com: 12V 5A Power Supply, Waysse Power Supply Adapter, AC DC Converter 100-220V to 12 Volt 5 Amp Transformer 5.5x2.1mm Plug for LED Strip Light DVR NVR Security Cameras System CCTV Accessories: Electronics
Well it did stabilize the values, in fact they were just as good as with my benchtop supply.

Re: "Not enough capacitance on regulator." The capacitance used is exactly what was called out in the data sheet. How much do you think I should use?

Paul__B,
Please tell me what is wrong with the 7805. It does get hot, but it puts out a steady 5.08V, can handle 1.5A if I remember correctly and I have a sizeable heat sink on it. I thought switchers induce more noise?

I haven't decided yet how many LEDs will be used. The original idea was one for each grill segment (bluetooth speaker very similar to this 1930's Art Deco Addison Radio | Retro radios, Antique radio, Art deco clock). That would be 8 vertical segments, plus 16 horizontal segments plus 1 or 2 for the dial area. So total of 26 LEDs. However, I believe I have an idea which will shrink that number, but I haven't tested it yet. So I'm counting on 26.
I didn't understand the last half of your statement about 2/3 ". . . unless your main 5V supply is live." Maybe you could rephrase that sentence and use small words.
I like the idea of placing the switch on the ground side and pulling it up, but I don't understand why it is better.

  1. Actually the potentiometers ARE connected to ground. Not shown in drawing
  2. Smoke literally came out of the Nano. I meant the Nano board, not mine. When I removed it from my board and invsestigated the fried component was the zener diode connected to the USB port on the underside according to the internet, the source of ALL great things.
  3. It is a clone. I got this one probably a year ago so I don't have a reference. All I can tell you is I have to use the "old bootloader" to communicate.
  4. Well I agree, but I didn't know what. Since that was the only change I had made after plugging BOTH my 12V AND the USB in to monitor many times, I figured I must have shorted something with a solder blob. But nope! See my reply to ALL next.

ALL,
With the fried Nano off the board, I checked for a short. None. I checked resistance between the pin and ground with the switch disconnected and got 12K. I plugged in the power supply and saw 12.2VDC on the input to the regulator and 5.08V on the output. I first plugged the USB cable into a new Nano (clone), just freestanding, but with my finger on the diode. No problems. No heat. I then plugged the Nano into my board, no LED strip or switch. When I plugged in only the USB, no problem, no heat. I then plugged in the LED strip. No problem, no heat. Then the switch. Same thing. So I uploaded the software that checks the state of the switch and with the pull-down resistor in place I now read HIGH with the switch closed and LOW with the switch in the open configuration. . . as it should. I have NOT yet plugged in the 12V power supply (without the USB) to see if my last working sketch still functions without smoke. But this thread has not reached consensus. TomGeorge seems to think I should not plug them both in at the same time. Paul__B seems to think that is ok with a Nano. I'd like to get more feedback as I only have like one more Nano left and this is supposed to be a Christmas present. As I mentioned, I have plugged them both in many times, yet SOMETHING smoked the board and unless somehow I had a short, like maybe I wasn't careful and one of the potentiometers was touching the board (not likely), it kind of seems like having both supplies at one time was the most likely cause.

Sorry for the long post and thank you for the help.

As you indicated the Diode was damaged, that would suggest too much current draw on the 5V line. The MBR0520, if that is what is on your board, is rated for 500mA, with a higher peak rating.
If the 5V line was shorted, and the PC supported it, then a current surge could have taken it out.
The Nano does not have a resettable fuse like the Uno has to protect the PC if more current was drawn.
Any chance the 5V line was shorted to Gnd briefly when powered from the PC?

Hi,
You cannot run everything, including the LED strip off the computer USB reliably.

I would have a 100uF or at least a 10uF capacitor in place of the 0.33uF capacitor.

Tom... :slight_smile:

profozone:
Re: "Echo dot 5V device." Well I'm not sure why it says "input 12V DC and 1.25 A" on the bottom or why it came with a 12V power supply. This is an Echo Dot 3. Should I be contacting Amazon?

I have an echo device in every room in the house, but no Dot-3's. The 12V requirement for the Dot-3 is news to me. (I see it as good news. 2 Amp chargers are hard to find.)

Don't use the 7805.
Use this and you can run the Nano and a lot of LEDs.

tobsun.jpg

tobsun.jpg

profozone:
I'm still subject to the ridiculous 100 post limit (MHO), so I will respond to all of you in order in one post:

Excellent idea! :grinning:

profozone:
Please tell me what is wrong with the 7805. It does get hot, but it puts out a steady 5.08V, can handle 1.5A if I remember correctly and I have a sizeable heat sink on it.

1 Amp, dissipating 7 Watts. Really?

profozone:
I thought switchers induce more noise?

Why would that be in any way relevant? This is not an audio circuit.

And what do you imagine is inside the Echo anyway?

profozone:
So total of 26 LEDs. However, I believe I have an idea which will shrink that number, but I haven't tested it yet. So I'm counting on 26.

1.5 Amps for all the LEDs alone.

profozone:
I didn't understand the last half of your statement about 2/3 ". . . unless your main 5V supply is live." Maybe you could rephrase that sentence and use small words.

If you connect USB only, and have a substantial load on the 5 V pin, it will likely shut down your USB. Or if the USB copes, burn out your 500 mA Schottky. So if you have the "5V" pin connected to other devices, you must power that side to prevent it loading the USB.

profozone:
I like the idea of placing the switch on the ground side and pulling it up, but I don't understand why it is better.

Because you are not connecting things to the 5 V line and putting it at risk of short circuits (and interference). Switches are often remote from the main circuit.

profozone:
When I removed it from my board and investigated the fried component was the Zener diode connected to the USB port on the underside according to the internet, the source of ALL great things.

It is a Schottky, not a Zener. As CrossRoads has pointed out, it is rated at something like 500 mA.

profozone:
3. It is a clone. I got this one probably a year ago so I don't have a reference. All I can tell you is I have to use the "old bootloader" to communicate.

Not generally a problem - my clones require the same. But goodness knows what the rating of the Schottky in these actually is! :astonished:

profozone:
TomGeorge seems to think I should not plug them both in at the same time. Paul__B seems to think that is OK with a Nano.

It is. Tom has not commented further, but seemed to have not realised what a Nano is. As you see in the circuit above, the Schottky prevents back-feeding from the "5V" pin to the USB port.

profozone:
I'd like to get more feedback as I only have like one more Nano left and this is supposed to be a Christmas present.

As long as you do not make mistakes ...

Remove the burnt out diode from the damaged board. While a Schottky is the proper one, an ordinary power diode will work, you just lose about 0.6 V on the "5V" line if using (only) USB power. So if you are using USB only for programming, it doesn't matter. :sunglasses:

profozone:
As I mentioned, I have plugged them both in many times, yet SOMETHING smoked the board and unless somehow I had a short, like maybe I wasn't careful and one of the potentiometers was touching the board (not likely), it kind of seems like having both supplies at one time was the most likely cause.

Except that there is no actual problem doing so. :sunglasses:

TomGeorge:
Hi,
You cannot run everything, including the LED strip off the computer USB reliably.

I would have a 100uF or at least a 10uF capacitor in place of the 0.33uF capacitor.

Tom... :slight_smile:

Please understand I'm not trying to be argumentative. I'm just trying to understand. I found this statement in the TI documentation for the 7805:
It is not necessary to bypass the output, although this does improve transient response. Input bypassing is needed only if the regulator is located far from the filter capacitor of the power supply.
Also this statement:
When using large capacitors at the output of these regulators, a protection diode connected input to output (Figure 15) may be required if the input is shorted to ground. Without the protection diode, an input short causes the input to rapidly approach ground potential, while the output remains near the initial VOUT because of the stored charge in the large output capacitor. The capacitor will then discharge through a large internal input to output diode and parasitic transistors. If the energy released by the capacitor is large enough, this diode, low current metal, and the regulator are destroyed. The fast diode in Figure 15 shunts most of the capacitors discharge current around the regulator. Generally no protection diode is required for values of output capacitance ≤ 10 μF.
Comments?

Paul__B

I said small words!

Again, not trying to be a pain in the butt, just trying to understand. You said, "1 Amp, dissipating 7 Watts. Really?" I do not understand this statement either. So you think the 7805 is essentially being driven too hard? It'll get too hot? I just turned on 26 LEDs and measured the current going into the entire circuit (7805, Nano, LEDs plus any losses). I turned the LEDs up until they drew the most current and it measured 410mA. With P=IV, that is a maximum of P=(0.41 * 12) = 4.92W. Did I mess that up?

The noise is relevant because, on another project I completed days ago, I had back EMF from a motor (despite being separated in turn by a relay, a transistor and an optoisolator) cause the digital pin on the Nano to become unable to switch states. This caused the relay to stay closed and leave the motor on. Despite protective diodes on the motor windings, I wound up only solving it by replacing the motor. But that's a different story. On THIS project, I think I mentioned earlier, a noisy power supply caused the inputs to the Nano to go out of range. I intend to add in a servo that will move an indicator to display what mode has been selected. The servo only runs for as long as it takes to move the needle about 16 degrees, so not very long, but with the noisy power supply the servo kept trying to move around spastically, like me. I bought a quieter PS and that solved the out of range problem. I don't know if it solved the servo problem because I smoked the board and haven't gotten back to that part yet. You have a very good point about the Echo, though. I measured the current a while back with the Echo installed, but that was with my benchtop power supply and no servo. Now that I have this new PS, I should probably plug the Echo in and turn on some tunes. See what happens.

Ok, so with this: "If you connect USB only, and have a substantial load on the 5 V pin, it will likely shut down your USB. Or if the USB copes, burn out your 500 mA Schottky. So if you have the "5V" pin connected to other devices, you must power that side to prevent it loading the USB." You are essentially saying I HAVE to have the external power supply. I actually figured that one out for myself, but I was also trying to investigate the servo problem I just mentioned and therefore needed to plug the USB in as well.

Roger that on the switch and pull-up resistor!

Yes, Schottky. That's what I meant. Often mess that up. I do the same thing with composite and component cable terminology.