Arduino nano Vin Pin gives 5V even if Vin is not connected

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We have one Eval board made for Atmega328P. But we are using nano board directly for processor section. Attached is the schematic. We had first version working correctly. But this time, as soon as 12V power is connected with the nano board connected to PC, nano board is going bad. Smoke is coming from nano board. We lost 3 boards now.  I am not sure what could be the reason (Recently I got 20 nano boards CH340 based from ebay and also got 20 main boards assembled). So not sure if entire lot of nano is having issue or somethng else)

Note that in the board, U8 (AMS1117-5) and P1 (PSM) are not mounted. JP1 is shorted so that nano board will supply 5V to the main board through nano connector. So 12V power through TB1 or J4 is mainly for relay. Otherwise entire board derive 5V from nano boards (either through USB or through Vin getting again from main board).

When I connect only nano board to USB port and measure the voltage at Vin Pin of nano, I see around 5V . Is this could be causing any problem when we connect 12V to Vin with USB connected? What happens if we give 5V input to a regulator's output pin? Do we get 5V at the input? Even I checked this in Arduino Uno and see that Vin pin gives 5V when Vin is not cnnected.

 

Or is this could be the problem associated with Cheap CH340 product?

 

 

 

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Well, STOP BLOWING UP NANOs TILL YOU FIGURE THIS OUT

 

You're wanting to run this on a 12v supply?

 

According to the schematic, the VIN pin goes to the input of the regulator and VUSB goes through a schottky diode to +5, which is also the output of the regulator. I'm not in the presence of one of my nano's to check, but I think the voltage on the vin might be undefined when powered by the USB and something high-impedance like your meter might read 5v. 

 

You're sure you're connecting 12v to pin 30? The picture at https://www.arduino.cc/en/upload... is a little confusing as it looks like VIN is the second pin from the top, but that topmost dot is actually the hole.

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I'd suggest that there is probably no regulator or diode in the cheapy boards. Applying 12V in this instance would equal smoke. Some investigation of the cheapy board is required.

Last Edited: Sat. Jul 9, 2016 - 11:15 PM
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I think the voltage on the vin might be undefined when powered by the USB 

I was thinking only C language has many undefined things, but in hardware there is nothing like undefined!laugh. I am not hardware person and so cannot comment further on this. I was thinking if we give input to regulator (such as 7805/AMS 1117) output, that will not be reflected in the input. I too suspect this cheap priced cheap nano board. I need to check it. 

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Oh, it'll have a regulator and the diode. The regulator is the 3 pin chip on the bottom with the heat sink tab soldered down. The cheap Chinese manufacturer just took the published grb files and put the published list of parts on it and there you go. I did manage to kill one once. I'm not sure how. When you plug it to the USB, the power led glows very dimly and the AVR doesn't run its program. Alas. Feel bad. I'm not going to spend much time troubleshooting a board I got 4 of for less than 10 bucks. I'll bet I made a mistake with power and zorched the poor little diode. I have some of those diodes around, maybe I'll... na.

If you don't know my whole story, keep your mouth shut.

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No, Cheap nano board does not use published schematic. They use CH340 for USB-UART and we cannot even find the company manufacturing this CH340!! I had briefly compared two schematics and there is a difference between these two. 

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You haven't looked too hard - there's datasheets on the web. The usb->serial is probably the least of your worries. I'd be sketching out what happens to vin.

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It is confirmed that external Vin is causing problem. CH340 and AMS1117-5 both burnt (I can see black spots). I now removed Vin pin and connected to my board (Both 5V and 12V supply is needed now if I need to use relay etc). Tested 15 boards and no issue. So cheap nano board has some issues. But not sure what it is. May be diode between VUSB and VCC. Or AMS itself that derive 5V from Vin.

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I'll remember not to power mine that way.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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What about posting a pic of your nano boards? From your message I can't understand if you have the regulator or not, I mean, without regulator it's not surprising if it blows up :)

 

I also have cheap chinese nanos, they have the MCU on top and the CH340 and AMS1117-5 on the bottom, never tried to power with 12V, but I might test with 6V just to see if the regulator is working. If it's not, 6V wont burn the atmega (abs. max. is 6V) or the CH340 (abs. max. is 6.5V), just overheat but not critically.

Last Edited: Sat. Jul 16, 2016 - 01:53 AM
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I'd sketch out the circuit first. Use a multimeter to 'beep' out where VIN goes to and compare this against the 'official' schematic. I'd guess there is no diode to isolate Vusb from VIN.

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Attached pictures. Note that I had 10 nano boards without any issues. Next lot only have issues. That too I bought separately from different Ebay vendors and not as 20PCs. 

I checked that Diode is connected between VUSB and regulator output and diode seems to be healthy. Able to power the board from USB, but since CH340 is gone, cannot check if processor is gone. I need to connect serial pins separately and see if that works.

In the burnt out boards, the resistance between 5V and Gnd is only 133 ohm whereas it is around 1.5K in healthy boards.

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Ok, so the regulator is completely burned. I have nanos exactly like yours, and others that are a little bit different. You can see in the picture attached, on the right, the one like yours, on the left, a different model.

 

I notice that my other model has more copper near the regulator and maybe that helps to spread heat and prevent the burning out, maybe your other nanos are also like this, so they survive. However, the AMS1117 is supposed to have thermal shutdown circuitry and this shouldn't happen... fake AMS1117, perhaps? check this: https://plus.google.com/+JamesSleeman/posts/Q5s4VmbQwj6

 

I got brave and decided to test my nanos with 12V, I observed no problems, the 5V rail was perfect, but they were not connected to anything, so they were "just" drawing about 20 mA current. In this situation, the regulator is dissipating (12-5)*20 = 140 mW power.

 

Now, the datasheet says:

 

Thermal Resistance:

 

SOT-223 package  ϕ  JA = 90°C/W*

* With package soldering to copper area over backside
ground plane or internal power plane ϕ  JA  can vary from
46°C/W to >90°C/W depending on mounting technique and
the size of the copper area.

So today is pretty hot were I am, lets say 30 ºC, if the thermal resistance was 90 ºC per watt my regulators should be at 30 + 90 *.140 = 42.6 ºC

 

However, if I was drawing lets say 200mA from the 5V rail of the nano the regulator would dissipate 1.4W and would heat to 156 ºC, maybe blow up.

But if the nano was well designed with more copper near the regulator, maybe the thermal resistance would be less, if it was for example 65 ºC/W it would only heat to 121 ºC and survive (from the datasheet, max is 125 ºC).

 

Maybe your application draws a lot of current from the 5V rail, so some nanos can handle it and others can't, depending on their thermal design.

 

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But if AMS is unable supply, USB should have supplied required current right? What I mean is as soon as AMS output goes below (VUSB-diode drop), PC should start supplying right? That means AMS output does not even drop leading to failure??

My board draws hardly 150mA and do not have any issue if I connect to PC. Also I remember like connecting these boards burnt boards directly to 12V without USB Power and did not have any problem (Not for sure though). May be I have to experiment by giving only 12V and see if AMS is getting heated up (I can try only after 2 weeks). I would not mind losing another $2.5 if that tells me the problem.

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Who knows? Maybe these are fake AMS that don't even have any overcurrent protection, so they just blow up? I searched and there are several people complaining about fake regulators that blow up in various conditions...

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Well, let's calculate this: (12-5)*.150 = 1.05w. That's a lot for that little regulator. At 90C per watt, you're looking at say 110C. Perhaps within the device's spec, but hotter than I like things to be. Perhaps you can power this thing from a switching regulator like this one: http://www.ebay.com/itm/PSU2-5-1...

 

If you don't know my whole story, keep your mouth shut.

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There are three voltage levels on the Nano clone.  There is Vin (pin #1) which is +7_+12VDC.  There is Vusb, which is about +4.9V, and there is Vcc, which powers the AVR and the CH340G.  This is about +4.3V with USB power and +5V with Vin power.   There is also a 3.3V source that comes out of the CH340G IC, but the amount of current available from this pin is undocumented.

 

The Schottky diode between the USB +5 (Vusb) and the AVR Vcc prevents the voltage from Vin from being applied to the Vusb when both the USB cable and the Vin power source are applied at the same time.  This is a common occurrence when the AVR is only using the USB for a COM channel and bootloading the program, and the main power for the Arduino comes from Vin.  Vin can be from +5.5V to about +15V, although at higher voltages the Arduino board will get noticeably warm.

 

When powered by the Vusb, the Arduino runs at about +4.3 to 4.5 volts DC, not +5V.  The Shottky diode drops about 0.3V, and Vusb is often less than exactly +5V.   It seems to be a characteristic of the AMS1117 regulator that if an input voltage is applied to the Vin that is less than the rated output voltage, then that input voltage will be passed to the AMS1117 output pin without damage to the AMS1117 IC.   This is why all the Nano clones have a +5 AMS1117 regulator instead of the +3.3V regulator in the original Nano designs.  If you put in +7V -- +9V into Vin, then the AVR Vcc is exactly 5 volts.

 

To make a 3.3V system from a Nano clone,  use solder wick to clear the solder from the cathode (the side towards the center of the Nano board) of the Schottky diode and lift this end of the component off the pad.   Then exchange the AMS1117 5.0V regulator for an AMS1117 3.3V regulator: (use the solder wick on the four IC pads of the AMS1117).  Lastly, connect a thin (AWG30 wire-wrap works best) wire from the cathode of the Schottky diode to the Vin of the AMS1117 3.3V regulator.   Now voltage from the Vin pin (@ 9V) goes to the input pin of the AMS1117 and 3.3V comes out onto the Arduino Vcc.  But the Schottky diode blocks this high voltage from going into the Vusb +5.   With no external voltage on Vin, the Vusb goes from +4.9 to about +4.5 through the diode, and then to 3.3V through the AMS1117 regulator.

 

I believe that your Nanos were damaged by accidentally applying +12 volts to the AVR/Arduino's Vcc pin (+5V) instead of the Vin pin.

Last Edited: Mon. Jul 18, 2016 - 09:17 PM
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Today when I connected 12V power supply to the board. Spark came in FDN340P (Q1 in page 3 of the schematic attached to original post). Nothing is connected to 12V line except the relays and ULN2003A common line. Please note that P1 (PSM module) and ASM1117-5.0 and C1 next to Q1 are not mounted on the board.

 

JP3 in Page 2 near the relays selects the relay voltage between 12V and 5V. Here we use 12V relay. Relay is driven by U2 (ULN2003A) Page 2.

 

Page 4 J16: Pin 32 is 12V input of the nano module and it is removed since I had lost 2 boards already. So there is no issue of nano board it looks as we discussed in earlier posts. The problem is mostly in our design. Note that even though spark came, board continued to work.

 

My doubt:

Some resistor may be needed to limit the current to relay coil? Is there a possibility of relay drawing high inrush current? Or any LC filter needed? I am using 12V 400 ohm coil resistance Leon relay (SC10-S-DC12V)

Or do I need to use higher voltage rating MOSFET FDN340P (instead of 20V may be 50V)?

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The Nano regulator has a maximum input voltage of 20V. There is likely thermal dissipation limit too, depending on 5V load and input voltage. I have used several and have not had issues, but for fear of problems, I went external using a LM2937 D2Pak.

The P MOSFET only has Vgs -4.5V.

It all starts with a mental vision.

Last Edited: Sat. Nov 19, 2016 - 01:02 AM
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The issue is now not related to nano. It is only 12V input and relay section issues. Does 12V input require any spike buster when relay is connected? May be a capacitor? I do not have anything in the schematic.

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It appears the ULN2003A has internal diodes for freewheel of coil current when turning off. Does the power supply handle load currents without dip or instability?

It all starts with a mental vision.

Last Edited: Mon. Nov 21, 2016 - 02:03 PM
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I had blown up a Nano after experiencing intermittent operation, wasnt sure what the problem was, started cutting wires off my (fake) nano, assuming I had wired something wrong. Ended up rewiring the whole design, worked fine during testing, just as I finished the build, I put the lid on, powered up, LEDs flashed then nothing.. could smell burned chips when I opened the lid (specifically the CH340 USB UART).. lots of troubleshooting later, I applied just 12v to Vin + Gnd pin and measured 5v out. When I apply power to my second semi-fried board, I get a bad smell, a high pitched static wine, and 8v on the 5v output.

I do have the heatsink drain pin on some FETs floating around in the enclosure, as well as an exposed LED ground pin, so its *possible* the FET drain shorted to ground as a mode of failure, (unlikely due to the fact that my FETs I dont think were plugged into their loads at the time). I am putting this down to faulty AMS1117 5v supply chips, which explains everything. External 5v regulators from now on.
Also here is a lovely breakdown of the fake Nano boards, including schematic. 

Last Edited: Sun. Sep 13, 2020 - 08:25 AM
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bingoringo wrote:
I am putting this down to faulty AMS1117 5v supply chips,

 

I'd suggest that something in your circuit precipitated the failure.

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Sorry to hear you smoked the board...

 

Welcome to the Forum.

 

Can yo post a schematic of your project?

(And perhaps a photo of the actual board?)

 

What was the overall current drawn by the system?

The linear regulator will get quite hot with a Vin of 12V if you draw much current from it.

 

You might put an ammeter in your power supply lead to see what the project is drawing.

If it is not roughly what you expect, then you have a short, or an I/O pin contention, or something else going on.

 

JC

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After several days of troubleshooting, measuring voltages and currents etc.. and rebuilding just about everything in my circuit, I think I figured out what at least one of the causes of trouble was, I had a BME280 module connected to the device, which I had actually repaired a few weeks ago - by reflowing a new sensor onto the module. My guess is that this attempt to reflow was intermittently causing a short. I was going to write up a schematic and post that, as I thought I may have designed something wrong. I have spend several days in a maddening process rewiring everything - except for the sensor itself. I have replaced the sensor, although the replacement is evidently only 3v3 capable.. realising this after rewiring the sensor cable several times.. Going to switch-out an ESP32 so that should be fine.. - The most frustrating part was thinking I had solved this issue, go to reinstall my system at differently location and each and every time have this issue magically reappear...

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Reflowing a bme280! That must've been 'fun'. I've tried that before - now I just buy the cheapy boards with the hard work done. Unfortunately my hands aren't good for 1/10mm precision.

 

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I guess watching hot air reflow videos on YouTube got my hopes up

Last Edited: Fri. Sep 18, 2020 - 11:44 AM