BeagleBone Black won't boot after wiring up LED strip w MOSFETs and separate 12V power supply

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I wired up a circuit with an LED strip, 3 N-channel MOSFETs, and a separate 12V power supply, with the gate pins on the MOSFETS connected to I/O pins on the Beaglebone.

When I didn’t connect the circuit to the Bone ground, I apparently fried 2 boards. Neither will boot up. One gives a flicker on the power light and then goes off, and on the other the power light turns on, but the other LEDs don’t flash and I can’t get into either board.

Here is the thread on the Adafruit forum with a photo of the circuit: http://forums.adafruit.com/viewtopic.php?f=8&t=69691&p=353330&sid=eff0f5bd69bba9338e6f0ec2d7fa70c4#p353330
The Adafruit support said that setup should not have hurt the board.

I checked the voltage on the gate pin on each MOSFET that was connected to the Bone and it was nominal (~200mA).

Does anyone have any ideas on this? How could this have fried 2 boards?

Thanks for any help.

And PS I posted this earlier today but didn’t see it show up in the forum. Sorry if it needed to be approved and you are getting a duplicate.

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I wired up a circuit with an LED strip, 3 N-channel MOSFETs, and a separate
12V power supply, with the gate pins on the MOSFETS connected to I/O pins
on the Beaglebone.

some mosfets have protective diodes on the gate inputs.

When I didn't connect the circuit to the Bone ground, I apparently fried 2
boards. Neither will boot up. One gives a flicker on the power light and
then goes off, and on the other the power light turns on, but the other
LEDs don't flash and I can't get into either board.

If I assume that the ground on the circuit didn't have a connection to
the BBB ground, and that the 12 volt supply was connected to the
circuit +12 and gnd, then you put floating lines on the BBB outputs,
and any leakage in the power supply to ground (or the BBB ground)
could put any voltage on the output pins of the BBB.

The gates were floating, which is why the circuit was unstable.

BTW: these had to be enhancement mode FETs for this to work.

Here is the thread on the Adafruit forum with a photo of the circuit:
http://forums.adafruit.com/viewtopic.php?f=8&t=69691&p=353330&sid=eff0f5bd69bba9338e6f0ec2d7fa70c4#p353330
*The Adafruit support said that setup should not have hurt the board. *

If connected properly.

I checked the voltage on the gate pin on each MOSFET that was connected to
the Bone and it was nominal (~200mA).

Voltage is not measured in ma, do you mean 200 mv?

The meter you used loaded the circuit, and would not show the true
voltage. It's not a matter of current into the chip, it's a matter of
voltage (period). The voltage can cause nasty things in the chip
transistors driving the pin, and the power supply of the chip itself
then does the damage.

Does anyone have any ideas on this? How could this have fried 2 boards?

A suggestion for you. Next time, do not make single connections to
pins on the BBB (or anything else unless you're quite certain of what
you're doing).

Best to take a ribbon connector that makes connections to everything
at once, run it to a breakout board, and then hard wire your
connections to that. A frequent problem in breadboards is wires
coming loose. This way the ground is automatically made to the chips
on the breadboard.

Another option would be to use a darlington transistor array, such as
the ULN2803 or the ULN2003 instead of the FETS. Again, the same
warning about grounding is in effect.

Since you have two non-functional BBB's I'd suggest taking a meter and
checking the voltages at the various regulators on the board. You
have a schematic, and it may be possible that you have a bad regulator
somehow. That's better than a fried CPU.

Harvey

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Thanks very much for your response Harvey. Right sorry on the mA, I meant mV.
Also I sent a picture of the circuit to the Adafruit customer support, it’s in that forum thread that I linked to. And they said from looking at it, it shouldn’t have been capable of frying the Bone.

I’m surprised I can’t find anything similar to this issue. I will check out the regulators.

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Thanks very much for your response Harvey. Right sorry on the mA, I meant
mV.
Also I sent a picture of the circuit to the Adafruit customer support, it's
in that forum thread that I linked to. And they said from looking at it, it
shouldn't have been capable of frying the Bone.

Pictures of the setup help little, except to find an uninstalled wire.
The picture you put on the forum shows connections to the strip, but
none to the drivers, nor from the drivers to the board.

A schematic would be good, as well as the part numbers of the FETS.
Otherwise, it's difficult to do anything but guess, although in this
case, the guesses might be decent enough.

I'm surprised I can't find anything similar to this issue. I will check out
the regulators.

Even in a relatively simple circuit, the number of ways that a circuit
can be miswired is about N! where you count the parts and the wires.
And that's just with miswiring, not forgetting something or adding bad
parts.

Hopefully, you damaged an easily replaceable part.

The outputs on this chip are relatively fragile. There are other
(perhaps older, perhaps a different design of chip) processors that
have more robust outputs.

Harvey

5

Hi Harvey,

I believe this is the main regulator pictured: TL5209, an LDO.

On our BBB I read 5V going into the board, but only 1V on the regulator input, and 0V coming out… What could that mean?

On Sam’s BBB I read 5V into and 3.3V out of the regulator. This board’s power light comes on and stays on, so that regulator seems fine. I’ll keep looking into this one.

BBB schematic: https://github.com/CircuitCo/BeagleBone-Black/blob/master/BBB_SCH.pdf
Regulator manual: http://www.ti.com/lit/ds/symlink/tl5209.pdf

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If I assume that the ground on the circuit didn’t have a connection to the BBB ground

Nothing to assume :slight_smile: , there is NO ground connection between the BB and the bread board from what the picture shows, just 3 wires (Red, Green, Blue) not 4.

If Adafruit said they could not see anything wrong with the wiring I would be very worried about their “technical support”

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Nothing to assume :slight_smile: , there is NO ground connection between the BB and the bread board from what the picture shows, just 3 wires (Red, Green, Blue) not 4.

How that could have damaged the BBB is what we don’t understand. The wires to the BBB were connected to the MOSFET gates.

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Right, Adafruit was aware there was no ground connection. They just said this should not have caused the BBB to fry from voltage running through the FET gate pins which were connected to the board.

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First of all, the output level from the GPIO is about 3.3V and MOSFETs are voltage controlled devices.

So you will need a transistor to boost the voltage to 12 volts.

Second: Do you have an actual schematic?

Third: Are you using P or N Channel MOSFET’s ?

Because high current versions like the ones you are using have a built in body diode …

Get back to us with more info, Ok

“No one could make a greater mistake than he who did nothing because he could do only a little.”

“All that is necessary for the triumph of evil is that good men do nothing” Edmond Burke (1729 - 1797)

http://www.packtpub.com/building-a-home-security-system-with-beaglebone/book

http://ca.linkedin.com/pub/bill-pretty/2b/b07/602

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Sure, thanks a lot for the continued help.

Here are the FETs that I used, which are N-Channel and can switch 30V/60A: https://www.adafruit.com/products/355

Here is the wiring I followed (diagram about half way down; first one that doesn’t have the 100-220ohm resistors): https://learn.adafruit.com/rgb-led-strips/usage
Except I connected the voltage wire on the LED strip to a separate 12V supply, and did not ground the circuit to the Beaglebone GND as you can see in the picture I posted on the Adafruit forum. They say at the bottom there in regards to connecting to separate 12V supply, “Make sure to connect the ground of that supply to the ground of the Arduino/MOSFETs!”, but in the forum post, they implied it wouldn’t burn out the board if I didn’t do this.

Here is the schematic of the LED strip: https://learn.adafruit.com/rgb-led-strips/schematic

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what you have done is fry the boards by not connecting the ground.

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Can you explain how that happened?

When I measured the gate pin on the FETs, it was only 200mV.

How would this fry the board, and what exactly would it fry on the Bone?

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1st of all IF you used the FETs shown on Adafruit they are logic level FETs, so you can drive them directly from the BB.

Resistors are only required if you had used the transistors instead of the FETs.

As discussed you missed the GND wire (Black) as shown on Adafruit.

Where did you measure the 200mV? From the BB GND to the outputs or elsewhere? As you don’t have a common GND readings are pretty much meaningless.

FETs have a “large” capacitance on the Gate, without a common ground you could have several hundred (or thousands) volts of static charge for a very short period, but it could be large enough to kill the processor. Very likely if you have carpets around.

If you unplug everything you added to the BB will it boot up again? If not the above may be possible.

You seem to be using P9_12, P9_16 and P9_21 they should be safe to use as I’m using them on a couple of projects without problems, you MUST add the GND wire from any pin 1 or 2 of either P8 or P9 to the GND track of your breadboard.

I may think of something else later on… meanwhile, as I said above, unplug everything from the BB and see if it powers up, if not it’s shopping time again.

14

Also, I believe the RasPi uses 5V logic while the BBB uses 3.3V logic /IO

“No one could make a greater mistake than he who did nothing because he could do only a little.”

“All that is necessary for the triumph of evil is that good men do nothing” Edmond Burke (1729 - 1797)

http://www.packtpub.com/building-a-home-security-system-with-beaglebone/book

http://ca.linkedin.com/pub/bill-pretty/2b/b07/602

15

JS-BBB, that’s about as good of an explanation as I’m probably going to get. I wish I knew exactly what it did to the board, but at least that gives me some peace of mind.

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Try this, instead of FET’s:

The IC allows you to have separate supplies for the logic and the ‘motor’.

So you can run the LED’s from 12V and the logic from 3.3V J

That’s how I drive motors ….

Bill

“No one could make a greater mistake than he who did nothing because he could do only a little.”

“All that is necessary for the triumph of evil is that good men do nothing” Edmond Burke (1729 - 1797)

http://www.packtpub.com/building-a-home-security-system-with-beaglebone/book

http://ca.linkedin.com/pub/bill-pretty/2b/b07/602

sn754410.pdf (154 KB)

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Nice, that looks like a great part. I’ll check into it for future prototyping. Thanks Bill

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在 2015年3月6日星期五 UTC+8下午2:41:17，gr…@sensa.io写道：

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most i/o pins cant handle 200ma.
you fried the processor.

It really helps to read the bone SRM to see the limitations.

you need buffers if you want to drive anything that high

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Is anything coming out from the uart console?