Electronics > Projects, Designs, and Technical Stuff
Adding an LED power indicator to vintage circuit
gkmaia:
I would like to add an LED to a vintage circuit as an indicator it is powered on.
My plan would be to add on a 12v rail that comes out of T1 pins 9 and 10.
Add a couple resistor as a voltage divider to bring the voltage down. By my calculations I will get about 2.04v at the LED with the divider.
Can someone with more experience let me know if its a good plan? Or any drawbacks of my idea with some viable suggestions?
StillTrying:
"My plan would be to add on a 12v rail that comes out of T1 pins 9 and 10."
There's already a LED there, or is that the one you've added.
SuperBright LEDs are bright enough as an indicator at 2 or 3 mA, so you can connect them almost anywhere there's DC.
"Add a couple resistor as a voltage divider"
A LED only needs one series current limiting resistor.
The polarity of C104, C105 and D107 look the wrong way around to me.
gkmaia:
The LED you see is the one I added.
That rail runs 12v. My LED runs 2.5v. Without a divider I may end up burning it or not?
Yes, they were wrong. Just fixed it thanks.
Benta:
You mention that is's vintage eq. In that case, I'd install a neon lamp across the 240 V line (don't forget a series resistor). Much easier.
pwlps:
--- Quote from: gkmaia on May 18, 2019, 09:18:31 am ---That rail runs 12v. My LED runs 2.5v. Without a divider I may end up burning it or not?
--- End quote ---
A LED is a diode: you drive it with a constant current, not voltage. Just put a resistor in series, for example to get 10mA it will be (12V-2.5V)/10mA that is around 1k.
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