Burned Moteino (need some help with wiring)

[Lukapple]

Hi guys,
I’m working on my “Gateopener” project, which includes Moteino and ULN2003AN darlington transistor array chip, which is used to control different things. One of them is an electric lock which is operated with 9-16V AC/DC electrical pulse (in my case 9Vdc). However it looks like I’ve done some critical error with wiring, because when I try to connect that electrical lock to ULN chip (pin labeled U5 on my custom PCB), it burned my Moteino.
Here is the wiring that I’ve used:




Any hints what did I wire wrong?

[TomWS]

From the schematic view, it appears correct, but there isn't enough detail in the PCB view to tell anything.  Did you do a DRC on the PCB to verify there were no shorts in the wiring?

[Lukapple]

I'm not 100% sure, but I think that I did a DRC check.
I'm attaching an Eagle project files in case if you want to see any additional details.

Hmm, one more thing, when I did this test, I had a pcb connected to external 9Vdc source, and moteino(on that custom PCB board) connected to my laptop using FTDI usb cable. When I connected the wires, my laptop also rebooted - I forgot to disconnect it before the test (unfortunately I didn't burn the usb port). Was maybe that the issue ? 
Or may it be that I connected wrong wires or something (for the test I held those wires with hands). I just want to make sure that wiring is correct, before I do another (burning) test.

[john4444]

Hi LukApple,
It looks as if your ULN is directly driving a relay coil.
Without a suppression diode, you can expect the kick-back from the
coil to wipe out almost anything connected to it.
A common 1N4000 diode is often the suppression device of choice and will
be able to adsorb the high-voltage pulse when the relay drops out.

Good Luck.

[Lukapple]

Hi,
Thanks for the hint. But isn't that protection already built-in ULN2003 chip? Do I have to use suppression diode anyway?
Does matter where in the circuit I place it? Is it ok, if i place it at M5 connector?

[TomWS]

Hi,
Thanks for the hint. But isn't that protection already built-in ULN2003 chip? Do I have to use suppression diode anyway?
Does matter where in the circuit I place it? Is it ok, if i place it at M5 connector?

Yes, that protection is inside the ULN2003, but you need to connect the COM pin (pin9) to the high side of the relay (VIN source).

I think VIN from your FTDI board and VIN pin on the Moteino are directly connected, which could have blown our your FTDI board, but not the Moteino. 

[Lukapple]

FTDI adapter looks good - it works fine with other Moteinos. When I connect "bad" Moteino, FTDI TX light is blinking all the time. And when I hit Upload sketch, it uploads infinitely.
I'm using official Moteino and FTDI adapter from Felix's shop.
I feel really bad for that brand new Moteino R6 with flash chip on it

If I connect COM to VIN source (high side of relay), I don't need that additional 1N4000 diode, is that corret?
So I simply do this additional connection (see red bolded line on COM connection - COM connected to "+"):


Can you confirm this PCB fix?

[TomWS]

If I connect COM to VIN source (high side of relay), I don't need that additional 1N4000 diode, is that corret?

Yes, that is correct.
So I simply do this additional connection (see red bolded line on COM connection - COM connected to "+"):

Can you confirm this PCB fix?

So, is this a new connection?

I'm not sure why your board shorted out.  The only thing I can think of is that, with the Moteino straddling the circuit underneath, underside traces on the Moteino accidentally touched pins on the ULN2003?

[Lukapple]

I've tried circuit on the breadboard with diode instead of electric lock and it works fine.


So I think that problem was because:
- I didn't have ULN2003 COM pin connected and like @john4444 said, kick-back burned my Moteino
or
- I accidentally touched wrong pin when I held those wires for test with my shaking hands 

There is enough space under Moteino, so it's not touching ULN pins





 

[Lukapple]

Hi,
I’ve tried to connect COM to VIN, but it looks like there is conflict with “U4” pin, which opens gate (it connects COM and PP pin on the gate opener motor - and I’ve noticed that there is 16VAC on that pin)


However, I’ve connected without that “COM” on uln2003 and added 1N4001 diode on the VIN - electric lock line, and everything works fine