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Old 09-15-2013, 06:09 AM   #1
alien
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Apr 2012
Philadelphia, PA
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Turn an inexpensive LED dimmer into a PWM timer for an electric element by swapping out a single capacitor:

Blog post: http://smokedprojects.blogspot.com/2...-pwm-hack.html




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Old 09-15-2013, 12:15 PM   #2
danb35
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Very clever! Should be pretty easy to feed this into an SSR and presto! Manual power control.



 
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Old 09-16-2013, 04:10 AM   #3
alien
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Exactly!

I have a spare so if anyone wants the 1.5 Hz PWM timer it is $10 shipped within the USA. Contact me via PM.

 
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Old 09-17-2013, 01:59 AM   #4
cank
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Great idea. I just ordered 2.
Thanks for sharing. I post how it goes.

 
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Old 09-17-2013, 02:12 PM   #5
alien
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Good luck! Desoldering the original cap was the hard bit (for me anyway).

There is a lot of electronics in one of these little dimmers for $4 or however much they are.

 
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Old 10-10-2013, 12:47 PM   #6
cank
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Alien,

I received my two dimmers but the circuit board is different. I have watched that video and looked at your pics and think I found which capacitor to switch but thought I should ask you first. Is there a way to verify which I one using just a normal multimeter? If my phone can upload pics I'll attach one of the boards.
I think it's C4?


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Old 10-12-2013, 05:49 AM   #7
alien
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I have a couple of spares knocking around. I opened them up and they are different again! The PCB is neither green nor blue, but maroon -- and all the components are very helpfully labelled part with numbers and values, as on yours.

One of the 8-pin chips should be marked NE555. Orient the chip so that the bar is at the top, and count the pins from the top left (1) to the bottom left (4) and back up the other side from the bottom right (5) to the top right (8). There might be a dot next to pin 1. The timing capacitor should be connected to pin 1 on one end (ground) and pins 2 and 6 on the other end. Some of the connections may be visible on the PCB, some may be underneath the chip and not visible.

On that basis it looks very much like C4 as you say, which has the same value that mine did (0.1uF), so swapping it for 47uF or 100uF should get you in the ballpark. Good luck!

 
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Old 11-07-2013, 11:22 PM   #8
cank
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Finally got around to trying this. My desoldering skills are quite lacking and I ended up just pulling the pads and everything off the board. I even thought there was some stray solder in the masking to I tried to pry it off, turned out it was some of the metal from the circuit, so I soldered the leg of the capacitor to pin 2 of the 555 chip and a bridge to the closest resister.


Hooked it up to a SSR and a pencil sharpener motor. Everything seemed to work great. I could vary the pulse from off to full on. One thing I noticed is that when I first plugged it in, even if the pot was in the off position it would send one small pulse to the motor and then stop.

Thanks for this great little gem. Now I gotta find time to try it out for an element.

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Old 11-08-2013, 12:54 AM   #9
alien
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With the lid on nobody will know. Actually I pulled one of the pads off mine and had to scratch away part of the mask to solder to the ground plane.

 
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Old 01-08-2014, 09:28 AM   #10
alphaomega
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Hi!
Sorry for reviving the thread, but I have some info to add if someone else finds this later.
I found this thread (and magic's page) after I already reverse engineered a similar dimmer and modded it to SSR freq. for a cheapo RIMS system I'm planning.
I also found that a 100uf cap got me in th 1Hz range.
The tip I have is, if you want to decrease freq. by adding capacitance, you can avoid desoldering the smd cap and risk damaging the pcb. You can just solder the new cap in parallell. This makes it easy to undo later as well.
I just cut the legs of the electrolyte to appropriate length, pretinned, added some fresh solder to the pads and soldered it in.
Cheers!



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