benny_profane
Well-known member
I typically use a 20k trim with whatever CLR (2k2-4k7). For white and blue, that added resistance can be useful.
-
BLACK FRIDAY SALE!
20% off all PCBs - No coupon code required - Valid through 12/01/2024
Components and sale items excluded
Took me long enough to see the light...
- Thread starter jhaneyzz
- Start date
jhaneyzz
Well-known member
I'm working on a recipe for electro luminescent in the lab.
eventually, my pedals will just glow with a ghostly shimmer...
Dirty_Boogie
Well-known member
Any clearer than that, and you'd might as well ship the boards with the CLR and LED pre-soldered, just to avoid any possible confusion!
jhaneyzz
Well-known member
Another blind spot on the same topic...
Since I test LEDs with a 3v battery I assume they NEED 3V. So a assumed the resistor lowered the VOLTAGE from 9V to 3V.
In the discussion mr smartypants @vigilante398 I mentioned that I measured the voltage with the CLR in place and "It's still reading 9V" to which he replied "yeah. it's supposed to" This is all coming back to me in retrospect. I wasn't drunk at the time...
So how can an LED rated for 3V handle 9V?
I predict the answer is going to be "it's the amperage stupid!" not that Nathan would call me stupid (out loud...)
Since I test LEDs with a 3v battery I assume they NEED 3V. So a assumed the resistor lowered the VOLTAGE from 9V to 3V.
In the discussion mr smartypants @vigilante398 I mentioned that I measured the voltage with the CLR in place and "It's still reading 9V" to which he replied "yeah. it's supposed to" This is all coming back to me in retrospect. I wasn't drunk at the time...
So how can an LED rated for 3V handle 9V?
I predict the answer is going to be "it's the amperage stupid!" not that Nathan would call me stupid (out loud...)
benny_profane
Well-known member
The forward voltage is the drop across the diode (same as when discussing diodes as clippers). The rating that you may be thinking of is the power rating (W).
P = I * V
en.m.wikipedia.org
P = I * V
Ohm's law - Wikipedia
benny_profane
Well-known member
What do you mean by appropriate?
jhaneyzz
Well-known member
Let's say I have a board from a PCB maker that doesn't prove build docs... (just sayin...)
I'm ready to finish the build, the last thing is soldering in the LED.
I'm going to use an orange LED because they're the best...
My led has a Forward Voltage of 2.1 and a forward current of 50mA
Can I test the LED pads with the board powered up and engaged, before installing, with my MM and know if it is going to melt, (i.e. No CLR)?
Or am I just not thinking about this the right way?
jimilee
Well-known member
You guys are way overthinking this. Work a little to figure out what you like and go with it. To me, it’s a personal preference once you get past about 500r. I aim for 4k7 but will settle for what ever I come across first that’s closest to it. For a blue LED, I will go higher. Why? I don’t know, it’s always been done that way.
benny_profane
Well-known member
Where are you getting that current figure? I don’t think a meter is going to tell you anything you don’t already know.
If your concern is frying the LED, reference the power rating, then use the ohm’s law and power formulas to calculate the resistor for your supply voltage.
A handy way to audition LED values is to use a breadboard and a trimmer. You can set up a trimmer as a variable resistor in series with the LED and adjust to preference. Measure the trimmer out of circuit to get the CLR to install in circuit. You should use an addition resistor in series to ensure you don’t go too low (unless you want an experiment showing the limit). If you do go too low, it’ll pop and smell terrible.
Is that helpful? I may still be misunderstanding what you’re asking.
coltonius
Well-known member
Waterclear blue, green, and white are the most offensive to our eyes because of the way we receive blues. I use a 10k resistor minimum for those.
UV and some of my diffused LEDs get 470Ω because they’re so dim.
Everything else (red, yellow, orange) typically gets between 1k - 4.7k, like you said. They’re less obnoxious so I’m not as worried.
jhaneyzz
Well-known member
At this point I'm actually asking "for science"
There is a conceptual gap I am trying to exorcise...
jhaneyzz
Well-known member
I guess that answer to my puzzle is that I could measure the resistance between + voltage and the LED pad, and - and ground) determine if there is a resistor in the circuit.
You see, I had it in my head that the CLR takes teh 9V down to 3V, and I could measure the voltage at the positive pad and if it read 9V = no CLR, 3V = yes CLR.
Now i realize that just isn't how that works....
You see, I had it in my head that the CLR takes teh 9V down to 3V, and I could measure the voltage at the positive pad and if it read 9V = no CLR, 3V = yes CLR.
Now i realize that just isn't how that works....
Barry
Well-known member
The CLR can be on the ground side or the plus side, if it's on the ground side you'd have to measure from the side that goes to ground.
Robert
Reverse Engineer
The CLR doesn't drop any voltage without current flow and with no LED installed there is no current flow so you'll always measure 9V on the pad regardless of whether a CLR is present or not.
If the PCB came from here and has pads for an LED (and isn't a breakout board) there is a current limiting resistor somewhere on that PCB.
... okay there was that one time....
Bricksnbeatles
Member known well
Pshhhhh… I just use a 2.7k resistor and make damn sure not to ever look directly at the pedal
Similar threads
