[sdiy] flashing LED?? blinking led FLED (are they internally similar to a UJT?)

Mr&MrsAccount hbissell at wowway.com
Wed Jun 12 18:27:05 CEST 2024


Long ago in a far distant galaxy (workplace)  
  
I put a flashing LED into one of our products in place of an error indicator. This meant the unit 
would always flash an error condition. 
  
My intent was to give the service techs a bit of a workout, hone their troubleshooting skills. 
  
They didn't notice. They shipped it to the customer, who returned it.  The flashing LED has some quiescent current when it is off, so the oscilloscope trace showed what looked like a command from the GPIO to flash, albeit with wrong logic levels. The current draw when ON was enough to pull the GPIO a little bit lower. 
  
When I came in, the chief engineer was puzzling over it.  I told him "I'll take care of it" and did. 
  
Last time I played a "practical joke".  So yes, I know about flashing LEDs 
  
For you other ancient ones.. Remember they had "flasher buttons" that fit below the bulb in an Edison socket to turn any incandescent lamp into a flasher.  EMI anyone ??? 
  
Harry 
   
   

-----Original Message-----

From: Ben <synth-diy at synth-diy.org>
To: Ingo <igg.debus at gmail.com>
Cc: SDIY <synth-diy at synth-diy.org>
Date: Wednesday, 12 June 2024 10:04 AM EDT
Subject: Re: [sdiy] flashing LED?? blinking led FLED (are they internally similar to a UJT?)

My pinball machines are full of them. :-)

> On 12 Jun 2024, at 14:11, Ingo Debus via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> Anyone remember self-flashing incandescent lamps? They had a bimetal strip in them. Once heated up, the bimetal interrupted the current, the lamp cooled down causing the the strip bend into the other direction, giving contact again, and so on…
> 
> Ingo
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