Somebody goofed up

[GeorgeOfTheJungle]

Or not? It's in a very popular dev board. Suddenly its magic smoke escaped today...

[bd139]

That sort of shit is why humans invented QA 

[martinayotte]

 

[fourfathom]

What is "LS1"?  It looks like the problem is there, and not the upside-down transistor.  I've seen people deliberately swap emitter and collector in order to get a slightly smaller saturation voltage (less gain, though).  That by itself shouldn't cause any smoke.

[Gyro]

What is "LS1"?  It looks like the problem is there, and not the upside-down transistor.  I've seen people deliberately swap emitter and collector in order to get a slightly smaller saturation voltage (less gain, though).  That by itself shouldn't cause any smoke.

It looks like a magnetic audio sounder (it would have to provide DC continuity for the circuit to 'work'). The GPIO stuck high would probably do it.

[bd139]

What is "LS1"?  It looks like the problem is there, and not the upside-down transistor.  I've seen people deliberately swap emitter and collector in order to get a slightly smaller saturation voltage (less gain, though).  That by itself shouldn't cause any smoke.

Fair point. Gain is close to unity doing this so I'm not sure what the deal is. Perhaps it was in the linear region too. Pd off the scale.

[magic]

If LS1 is something inductive it may easily avalanche the BE junction. People say a lot of bad things about avalanching BE junctions, I don't know how true they are

[GeorgeOfTheJungle]

That NPN has become a short circuit, and as the thing is powered by a LiPo, the LiPo went smoking hot as well. I was trying different "beeps" to find out which one seemed louder/could be heard from farther away, gpio 26 was outputting a square wave @2.8 kHz when it happened...

[thm_w]

DET402-G-1 attached, seems like the top cover is missing in OPs photo for some reason.
And it does appear to be coil based, which would give a voltage spike.

[rsjsouza]

What is "LS1"?  It looks like the problem is there, and not the upside-down transistor.  I've seen people deliberately swap emitter and collector in order to get a slightly smaller saturation voltage (less gain, though).  That by itself shouldn't cause any smoke.

A.k.a. common collector configuration.
https://en.wikipedia.org/wiki/Common_collector
 

[Circlotron]

What is "LS1"?  It looks like the problem is there, and not the upside-down transistor.  I've seen people deliberately swap emitter and collector in order to get a slightly smaller saturation voltage (less gain, though).  That by itself shouldn't cause any smoke.

A.k.a. common collector configuration.
https://en.wikipedia.org/wiki/Common_collector

If that’s the case, the power supply rails are reverse polarity.

[GeorgeOfTheJungle]

Now that I think about it, I was flipping gpio every 350 µs, but that's not 2.8 kHz, it's 1.4 kHz. Since it's close to the resonance frequency of the DET402-G-1, could that have accelerated the unfortunate events?

Code: [Select]

: invert 0= if 1 else 0 then ;

26 output: speaker
: beep
    begin
        speaker speaker digr invert digw
        350 delay.us
        key?
    until
    speaker 0 digw
;


[fourfathom]

What is "LS1"?  It looks like the problem is there, and not the upside-down transistor.  I've seen people deliberately swap emitter and collector in order to get a slightly smaller saturation voltage (less gain, though).  That by itself shouldn't cause any smoke.

A.k.a. common collector configuration.
https://en.wikipedia.org/wiki/Common_collector

Not the same thing at all.  Look again.

[fourfathom]

Now that I think about it, I was flipping gpio every 350 µs, but that's not 2.8 kHz, it's 1.4 kHz. Since it's close to the resonance frequency of the DET402-G-1, could that have accelerated the unfortunate events?

Code: [Select]

: invert 0= if 1 else 0 then ;

26 output: speaker
: beep
    begin
        speaker speaker digr invert digw
        350 delay.us
        key?
    until
    speaker 0 digw
;
Quite possibly. Depending on Q, the voltage ringing might well be high enough voltage to kill the transistor, especially in the upside-down config.  This could be a problem at any frequency. But driving it at resonance could make it worse.

[SiliconWizard]

Oh well, do NPNs not have a right to be used inverted? Maybe some of them just feel "right" when used this way.

[Kjelt]

Found the culprit in a different topic, she is the one that goofed up 

https://www.eevblog.com/forum/chat/gender-politics-has-now-infected-engineering-as-well/msg2667105/#msg2667105

[SiliconWizard]

Found the culprit in a different topic, she is the one that goofed up 

https://www.eevblog.com/forum/chat/gender-politics-has-now-infected-engineering-as-well/msg2667105/#msg2667105

Oh, I was not that far away then!

[Ian.M]

IMHO its just a shitty design.  If the transistor can't stand the max. current the sounder will pass @3.3V DC, they should have included a series resistor to limit the continuous current, possibly with a  capacitor across it so you can get more drive when you pulse it.   Also relying on reverse E-B zenering to turn the transistor on and clamp the back-EMF from the inductive load is just plain nasty.

Alternatively they could have used a NPN+ PNP pair as a complimentary emitter follower, and a capacitor in series with the sounder - that's particularly robust because the non-active transistor will turn on enough to clamp the output if the load tries to drags it more than one Vbe outside the rails.

[Sal Ammoniac]

Now that I think about it, I was flipping gpio every 350 µs, but that's not 2.8 kHz, it's 1.4 kHz. Since it's close to the resonance frequency of the DET402-G-1, could that have accelerated the unfortunate events?

Code: [Select]

: invert 0= if 1 else 0 then ;

26 output: speaker
: beep
    begin
        speaker speaker digr invert digw
        350 delay.us
        key?
    until
    speaker 0 digw
;


There's your problem right there... Forth killed it. When the transistor saw it was being controlled by Forth, it did the only thing it could: commit suicide. 

[SiliconWizard]

There's reason in controlling an inverted transistor with an inverted language.

[bd139]

There's your problem right there... Forth killed it.

I actually just spilled coffee everywhere laughing at that 

[GeorgeOfTheJungle]

Where's techman-001 ?

[techman-001]

Where's techman-001 ?

Just stumbling across this topic right now

I think the inductive load and possibly the on/off frequency killed the transistor being used in "uncommon emitter mode".

I think it may have also killed it if it was in common emitter mode.

George is that Forth your "ATlast" ?

[GeorgeOfTheJungle]

George is that Forth your "ATlast" ?

Yes it is. The only other Forth I've ever had (and used) is one for the Apple II that John Drapper (a.k.a. Captain Crunch) in person sold me at the NCC in NYC in 1979.

Edit:
But that code above won't run in yours because I've added some words to mine: e.g. delay.us (delayMicroseconds), digr (digitalRead) and digw IIANM.

[techman-001]

George is that Forth your "ATlast" ?

Yes it is. The only other Forth I've ever had (and used) is one for the Apple II that John Drapper (a.k.a. Captain Crunch) in person sold me at the NCC in NYC in 1979.

Edit:
But that code above won't run in yours because I've added some words to mine: e.g. delay.us (delayMicroseconds), digr (digitalRead) and digw IIANM.

Just having bought a Apple II from Captain Crunch makes you a legend!

Yes I could see your extra Words.

Forth people never copy each others code, for one we don't need to, and 2) our systems are all different.

Your code is:
: invert 0= if 1 else 0 then ;

26 output: speaker
: beep
    begin
        speaker speaker digr invert digw
        350 delay.us
        key?
    until
    speaker 0 digw
;

Mine would be something like:
( not inverts all bits)

 : beep
    begin
           speaker dup digr not digw
           350 delay.us
           key?
   until
   speaker 0 digw
;