Author Topic: Adding an LED power indicator to vintage circuit  (Read 1102 times)

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Offline gkmaiaTopic starter

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Adding an LED power indicator to vintage circuit
« on: May 18, 2019, 07:39:53 am »
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?
 

Offline StillTrying

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Re: Adding an LED power indicator to vintage circuit
« Reply #1 on: May 18, 2019, 09:10:00 am »
"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.
.  That took much longer than I thought it would.
 
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Offline gkmaiaTopic starter

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Re: Adding an LED power indicator to vintage circuit
« Reply #2 on: May 18, 2019, 09:18:31 am »
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.
« Last Edit: May 18, 2019, 09:21:24 am by gkmaia »
 

Offline Benta

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Re: Adding an LED power indicator to vintage circuit
« Reply #3 on: May 18, 2019, 09:25:08 am »
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.
 
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Offline pwlps

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Re: Adding an LED power indicator to vintage circuit
« Reply #4 on: May 18, 2019, 09:53:21 am »
That rail runs 12v. My LED runs 2.5v. Without a divider I may end up burning it or not?

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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Offline gkmaiaTopic starter

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Re: Adding an LED power indicator to vintage circuit
« Reply #5 on: May 18, 2019, 10:25:35 am »
Went with a neon as per L101. Thanks for the tips!
« Last Edit: May 18, 2019, 10:27:33 am by gkmaia »
 


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