LED power supply

[LinuxMan]

Hi.

I was just thinking about making myself an 8 effects powering unit (9v) and
was wondering if there was a way to add autosensing LEDs to the box for
every channel? What I meant by that is that I need the appropriate LED light
up if a current channel is in use (powering the effect). Say for example I had
3 effects powering from #1, #2, #3 channels of my powering unit box. That
way those 3 LEDs would lit up and the other 6 wouldn't.

The unit I have in mind as a base is this one: Spyder


Thanks
LM

[niftydog]

yes, there is a way. You need a current sensing resistor in series with the supply that will operate a transistor switch to turn on the LED.

At a certain current, the resistor should develop enough voltage accross it to turn on the transistor - and hence the LED.

The problem is, it also has the effect of dropping the supply voltage by the amount across the resistor. So, perhaps the best way is to put it before the regulators and make sure you still have enough voltage for the regulators to do their job. Also, go with a small value resistor to reduce this effect.

You'll need to measure the "standby" and "on" currents so that an appropriate resistor can be calculated. Also, be aware of the power disipated by the current sensing resistor!

Then, it's a matter of plopping a LED in the collector circuit, perhaps with a current limiting resistor, ground the emitter and away you go!

[LinuxMan]

Hi and thanks for the answer.

Are you thinking about something like this:


(Sorry about the screwy graphics but it serves the purpose.)

OK, after that I connect point A to the Spyder circuit after the DB01 and
before 78L09. Right? First value resistor (going to the base) should be
calculated.

Thanks for your help again...
LM

[niftydog]

Actually, I wasn't thinking straight... try something like this; insert this just before the regulator. You want to calc. the base resistor to develop just enough voltage accross it at the appropriate current, but not TOO much voltage or you're wasting energy. Also, keep in mind the power dissipated by the resistor. Also, calc. the LED current limit resistor!

Code Select Expand


 o-------o
 |       |
 |      .-.
 |      | |
 |      | |
 |      '-'
 |       |
 |       |
 |       V LED
 |       -
 |       |
 |       |
 |     |/
 o---o-|
 |     |>
 |       |
 |       o
 |  ___  |
--o-|___|-o--TO REGULATOR


[Dylan]

Aren't there any switched power jacks that could do something like that?

[niftydog]

well, you could do it that way, yes. But this solution allows you to have everything hard wired (no unreliable connections) and will only indicate when there is significant current being drawn from that transformer winding; not just when a cable is plugged into a socket.

[LinuxMan]

Ok,

I'll try that when I put mine together. Good point about the switched power
jacks.

Oh yeah, and that's a nice piece of ASCII there .

Thanks for help
LM

[Lonestarjohnny]

I don't have that problem, my pedal's stay plugged in all the time and i hardwire the cable end to the power supply, less plug's = less problem's,
Got 1 led for my power supply and each pedal has an LED to tell me it's on, that's all I need,
Johnny

[LinuxMan]

Glad it works for you Johnny...

I have something different in mind though. Let's say one of the power supply
outputs fails on stage. This way I could easily see exactly where the problem
is as there is an indicator... Plus I just love those glowing leds :idea::idea::idea: ... Oh,
so shiny...  

Cheers
LM

[Lonestarjohnny]

Linux, Your just LED Happy, Glad they are cheap lil Beggers for ya,
Johnny

[Lonestarjohnny]

all kidding aside LED's do look good, if your looking for some good dc cable's for hooking up your pedal's i use mouser's part no. 172-4000,
it has a 72 " cord with 1 right angle 2.5 id 5.5 od barrel. i cut the cord to lenght, hard wire under my board to the voltage rail, then do a nice routing to hide my cord's, these work great if you buy the matching dc jack from mouser. i alway's buy a 100 at a time and they run about a buck a piece.
Johnny

[LinuxMan]

Heh.

Yeah, they are cheap 'lil buggers .

That Mouser cord looks OK. It's nice to have a neat fx-board. But I think I'll
still go for the variation with plugs on both end. I don't think they have that at
Mouser...

Cheers
LM