rack panel art and some unrelated questions

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4/20/2003 6:27 PM

bosephus

rack panel art and some unrelated questions here are a few other things i have drawn up. maybe they are alright? true amp porn im telling ya!!!!                     and i finally got around to doin the true layout for my logic board (aiken's 3 channel footswitch). i need somebody to check my work to make sure i did it right. the view is from underneath the board where i will be soldering. im using header pins and connectors to attach the switches, the LEDs, and the DIN connector. it will be on a radio shack pad per hole board. also, to the right, is an interface circuit i drew up. will i need a dropping resistor on that circuit? doesnt seem like i would need one, since the LED's will be in series.     http://www.villagephotos.com/viewpubimage.asp?id_=2258459       thanx for your help!!     bosephus

 

4/21/2003 3:25 AM
Don Symes	You still need the dropping resistor - maybe a different value - but you MUST have that resistor.     To get the value, decide what LED current you want - probably 10mA, then:     Rseries = (Vsupply - how_many_leds_in_series*Vf_led)/Iled     HTH!     Nice art, BTW.

 

4/22/2003 7:16 PM

bosephus

i forgot another vactrol that will be in that switch circuit. so w nominal voltage of each LED of 2 volts, run in series, would be 6 volts. they will run fine on 5 volts. plus, ill be using a voltage regulator, so voltage or current wont be able to rise. am i correct in this? i have another box running relays. the relay coil leads are being run out to the foot switch box, w an LED in series w the switches. voltage is 5 volts, no current linit resistor. LED's havent died, yet/ regulated voltage of 5 volts.

 

4/23/2003 1:15 AM
Don Symes	quote: "the relay coil leads are being run out to the foot switch box, w an LED in series w the switches. voltage is 5 volts, no current linit resistor."   What's saving those LEDs is the DCr of the coils acting as current limiters.     The 3 LEDs in series on 5V may work (I'm curious to know) - but you should try to check the current just to make sure.     HTH!

 

4/23/2003 3:22 AM
bosephus	ill make a note to check on that. another question, or so. i was told that LED's are mostly constant current devices. which means they draw 20 ma at 2 volts or 5 volts or 20. am i incorrect in this?     bosephus

 

4/23/2003 4:47 AM

Don Symes

quote: "am i incorrect in this?"     You have it sort of sideways:     A forward-biased LED drops 2 volts (or so - it varies a bit with If), and can deal with up to (usually) 20mA without blowing up immediately.     If you don't take some step or other to limit current, an LED will happily TRY to pass all the current you can supply ... briefly.     That 20mA is most likely the LEDs If(max) rating - the do.not.exceed number. LEDs do burn out, and the closer you are to that limit, the sooner it happens.     Going back to the relay example; you're getting away with using the relay coil a a current limiting resistor because the coil current isn't very high. Try to do that with a higher-power relay (higher coil current) and your LED will toast itself pretty quickly.     HTH!

 

4/24/2003 12:22 AM
bosephus	thats coool. was trying to make it easier on myself, by running series LED and vactrols. less wire. parallel it is, w dropping/current limiting resistors!! thanx for your help.     bosephus

 

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