Spike Brewing 12.5 Conical Fermenter Giveaway - Enter Now!

Home Brew Forums > Home Brewing Beer > DIY Projects > More illuminated switch questions

Reply
 
LinkBack Thread Tools
Old 06-23-2010, 12:34 PM   #11
TriangleIL
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Chicago
Posts: 267
Liked 2 Times on 2 Posts
Likes Given: 2

Default

Quote:
Originally Posted by mattmauriello View Post
google images is my friend.... check this out:

Dont worry about R1 and C1 in those pictures, they're a little over kill. just keep your resistor (R2 in these pictures) high enough. the 3.6 kOhm that Bjorn suggested is probably perfect. the idea is that when current goes one way, it passs through the LED only. when reverse, it passes through the diode. since it passes (and its shorted through), there is negligible reverse voltage build up. if you just put them in series, the revers voltage stays, and all you've done is cut it in half, and since most LEDs break down at low reverse voltages, it wont cut it.
Are you saying we don't need R1 and C1, or are you saying the values are too high on those? If too high, what do you recommend for R1 and C1?
__________________
TriangleIL is offline
 
Reply With Quote Quick reply to this message
Old 06-23-2010, 12:50 PM   #12
Bjornbrewer
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2008
Location: St. Clair Shores, MI, USA, Earth, Sol System, Milky Way
Posts: 428
Liked 3 Times on 3 Posts

Default

you don't need them. They are actually quite pointless and only add components and complexity for no reason. You just need the diode and one series resistor (R2 in that schematic).

The capacitor is there to limit the diode/LED current...it acts as a resistor of sorts. R1...i think that's there for stability only (dampen oscillations) and R2's only job is to reduce charging current of the capacitor. If you take out the capacitor there is no need for the dampening resistor and then R2's function will be to limit the diode/LED current. The advantage of this circuit with the capacitor is that you don't need a big 5W resistor to limit the diode/LED current. So if size is a problem, this may be a better circuit, but I don't think that's an issue.

__________________
Sand Viking Brewery

“Happiness? A good cigar, a good meal, a good cigar and a good woman - or a bad woman; it depends on how much happiness you can handle.” ~George Burns
Bjornbrewer is offline
 
Reply With Quote Quick reply to this message
Old 06-23-2010, 02:57 PM   #13
erik
Feedback Score: 0 reviews
Recipes 
 
Join Date: Apr 2010
Location: San Jose
Posts: 48
Default

You guys rock! Thank you!

I have ordered diodes and resisters (ebay) and will build this as soon as they show up.

__________________
erik is offline
 
Reply With Quote Quick reply to this message
Old 06-23-2010, 03:44 PM   #14
Bjornbrewer
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2008
Location: St. Clair Shores, MI, USA, Earth, Sol System, Milky Way
Posts: 428
Liked 3 Times on 3 Posts

Default

let us know how it works out

__________________
Sand Viking Brewery

“Happiness? A good cigar, a good meal, a good cigar and a good woman - or a bad woman; it depends on how much happiness you can handle.” ~George Burns
Bjornbrewer is offline
 
Reply With Quote Quick reply to this message
Old 06-23-2010, 05:00 PM   #15
TriangleIL
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Chicago
Posts: 267
Liked 2 Times on 2 Posts
Likes Given: 2

Default

Excuse my ignorance here ...

For the following LED Multi colors, it shows the forward voltage as ~ 3.1V for most LEDs, and then ~ 2.1 for the red and yellow LEDs. For the 2.1V LEDs, will I need a different Diode/Resistor combination?

Thanks!

__________________
TriangleIL is offline
 
Reply With Quote Quick reply to this message
Old 06-23-2010, 05:44 PM   #16
Bjornbrewer
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2008
Location: St. Clair Shores, MI, USA, Earth, Sol System, Milky Way
Posts: 428
Liked 3 Times on 3 Posts

Default

ignorance excused!

The diode will stay the same, but the resistor may change. Use the formula I used on the first page except the source voltage will be 120V (instead of 12 or 6)

Example)

Vled = 2.1V
R = (120-2.1)/20mA = 5895 ohms

Vled = 3.1V
R = 5845 ohms

practically you should use a 5.9kOhm resistor (or close) and you'd be good with any of those LED's.

You should know the forward current of the LED as well, but 20mA is a typical value.

__________________
Sand Viking Brewery

“Happiness? A good cigar, a good meal, a good cigar and a good woman - or a bad woman; it depends on how much happiness you can handle.” ~George Burns
Bjornbrewer is offline
 
Reply With Quote Quick reply to this message
Old 06-23-2010, 06:31 PM   #17
TriangleIL
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Chicago
Posts: 267
Liked 2 Times on 2 Posts
Likes Given: 2

Default

Bjorn,

Awesome, thanks a lot. This makes perfect sense now. Have to remember all my college electronics equations

Thanks again!

__________________
TriangleIL is offline
 
Reply With Quote Quick reply to this message
Old 06-23-2010, 06:41 PM   #18
mattmauriello
HBT_LIFETIMESUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Apr 2010
Location: Silver Spring MD
Posts: 77
Liked 1 Times on 1 Posts

Default

Bjorn pointed this out, but it may have gotten lost...

Quote:
The advantage of this circuit with the capacitor is that you don't need a big 5W resistor to limit the diode/LED current
sice we're keeping the circuit simple, we need it. most commonly, resistors are 1/4 watt, meaning they can dissipate .25 watts of current without blowing up. in this case we're dealing with about 2.5 watts:
power (watts) = current x volts
20ma x (110 volts - 2.1v across led) = .02 x 107.9 ~= 2.2watts
so, while the 5 watts maybe a little high, its safe. id get 2.5 watt resistor minimum.
__________________
mattmauriello is offline
 
Reply With Quote Quick reply to this message
Old 06-23-2010, 07:13 PM   #19
Bjornbrewer
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2008
Location: St. Clair Shores, MI, USA, Earth, Sol System, Milky Way
Posts: 428
Liked 3 Times on 3 Posts

Default

Quote:
Originally Posted by mattmauriello View Post
sice we're keeping the circuit simple, we need it. most commonly, resistors are 1/4 watt, meaning they can dissipate .25 watts of current without blowing up. in this case we're dealing with about 2.5 watts:
power (watts) = current x volts
20ma x (110 volts - 2.1v across led) = .02 x 107.9 ~= 2.2watts
so, while the 5 watts maybe a little high, its safe. id get 2.5 watt resistor minimum.
with how ratings of resistors are so skewed and most are rated with a 50% duty cycle or some ungodly high temperature rise, it is good practice to double the power capability of the resistor. I think I mentioned this on the first page. If you calculate 2.2W, use a 5W or greater.

most resistors will NOT handle the power that they are rated for...don't ask me why, it's just a BS ratings game. I deal with it all the time at work.
__________________
Sand Viking Brewery

“Happiness? A good cigar, a good meal, a good cigar and a good woman - or a bad woman; it depends on how much happiness you can handle.” ~George Burns
Bjornbrewer is offline
 
Reply With Quote Quick reply to this message
Old 07-01-2010, 11:39 PM   #20
Quaffer
Feedback Score: 0 reviews
Recipes 
 
Join Date: Dec 2008
Location: Snohomish, WA
Posts: 488
Liked 24 Times on 15 Posts
Likes Given: 1

Default

Quote:
Originally Posted by mattmauriello View Post
Quote:
Originally Posted by TriangleIL View Post
Are you saying we don't need R1 and C1, or are you saying the values are too high on those? If too high, what do you recommend for R1 and C1?
Does anybody still care about this? Here's my input on this whole thing.

C1 is doing the heavy lifting in this circuit. The power dissipation (heat) of the original circuit is mostly eliminated by using the reactance of C1 (no power dissipation), which is the point of using C1. The circuit without the cap will get hot, while this one wont. For the 110V circuit example, C1 sets the LED current to 19mA or so, but only for half a cycle. On the average the LED will glow as if it had about 9.4mA through it constantly. Bigger capacitor, more current.

The purpose of R2 is to limit inrush current should you be unfortunate enough to plug in the thing when the voltage is at its peak, about 156V for the 110V AC circuit. That could destroy the LED or the diode. The 1K resistor limits the peak inrush current to 156mA, which dissipates quickly as the capacitor is charged. During normal use R2 dissipates about 0.36W, so 1/2W might work but 1W rating is a safer choice.

The purpose of R1 is to discharge the capacitor after you unplug the circuit so that you will not get a shock from it. It has negligible power dissipation. Eliminate at your own risk.

I used the 110V example of the schematic to calculate values. They will be a little higher using a 120V supply (9%).

Is that more information than you wanted?
__________________

Alcohol, the source of - and solution to - all of life’s problems. H.J.S.
My keezer, My E-brewery build thread, How I soldered 1" nut for heater

Quaffer is offline
 
Reply With Quote Quick reply to this message
Reply


Quick Reply
Message:
Options
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Illuminated switch bkloos DIY Projects 9 05-27-2010 02:07 AM
Illuminated Switch question maxbing DIY Projects 2 04-25-2010 12:51 PM
Automation Direct Illuminated Switches thorongil DIY Projects 4 04-21-2010 01:34 AM
ON/OFF Switch questions MrShake DIY Projects 8 01-19-2010 05:42 PM