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 Post subject: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Sun 14, 2018 6:02 pm 
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Location: Indianapolis, IN
Hello All,

After reading Matt Kroll's post in the Transistor Radio forum about converting his Zenith Royal 3000 T/O dial illumination to LED's, decided to do the same myself and it looked great. A package of 100 "warm-white" LED's were purchased on Ebay for $7.99 including shipping. After performing a "reversible" retrofit on my Royal 3000, also built a "strip" for a '63 Cadillac Wonderbar dial-light and yesterday, a removable "cluster" for an Arvin 3588...

These LED's are rated for 3-3.2 Volts on package and are VERY bright at this voltage level. Was thinking about other possible uses for these besides radio and remembered an LED light pen given me by a cousin which I've used often working at the bench. It's light output isn't nearly as bright, but has been valuable in several situations. I have several old test probes in junk "stash" and thought that one of these LED's could be easily mounted in it---and also have several NOS 5V wall-warts which would be a great power source. Played with resistor values and found that a 91 ohm would limit current to level which gave 2.9 Volts at LED with no noticeable difference in brightness from maximum and would hopefully extend its life. After wiring, wrapped a few turns of tape on cord to make it fit snugly in probe and provide some strain relief---also folded a piece of thin cardboard and pushed in at other end for further support.

The light works perfectly, is very lightweight, and doesn't depend on batteries so it can be left on for long periods. It will easily light up tight corners of crowded chassis and is more than bright enough to shine through circuit boards to examine for cracks. And these LED's have a wider angle of 120 degrees, so they illuminate a broader area !

This is a very simple project and I'm sure that all here would benefit by making one. Any regulated wall-wart would work with proper current limiting resistor or even a long cord with clips or banana plugs for use with bench supply (or even a "remote" battery pack). You could even tape this on a longer piece of rigid material to get into deeper areas such as under or behind cabinets. Many, many uses around the home...

Pics below...

John


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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Sun 14, 2018 7:17 pm 
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Joined: Jan Sun 06, 2008 3:28 am
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Location: Richmond, VA
John, that is a great tool. I have a LED penlight my wife gave me some time ago, but as you noted, they really aren't that bright. I will give that a try, perhaps using an old ball point pen barrel. A plastic probe might be better than a metal penlight around a hot chassis :roll:

Thanks!

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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Sun 14, 2018 8:39 pm 
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Joined: Dec Sun 21, 2014 6:37 am
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Location: Portland, TN, USA
An idea definitely worth stealing.

Thanks, John.

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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Sun 14, 2018 8:55 pm 
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Location: North of Mpls, Minnesota
Or you can just buy one for a couple of bucks.
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Dave


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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Sun 14, 2018 9:32 pm 
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Location: Oakland Township, Michigan
Thanks John! Great idea. It offers that familiar feel of a test lead probe that we're all so used to.

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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Mon 15, 2018 2:46 am 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Thanks Guys !

Ed---an old, plastic ball-point pen barrel is another good option for handle ! Used to save 'em years ago...

Chuck---feel free to put it into production !

Dave---I really like that Borelite, but mine only cost 8 cents for LED and a few minutes time (and doesn't need, but could use batteries)...

Matt---your warm-white LED's have opened up a whole new avenue of projects !

John


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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Mon 15, 2018 3:08 am 
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Here is my knock-off, using a plastic Bic barrel. I found a 3-volt/300mA wall wart, but it was cranking out nearly 5 volts with no load, so I used a 47 ohm resistor to bring it down to 2.9 volts. I glued the LED in the tip with a drop of CA, and used some shrink wrap (heat carefully) at the back end. I used one of my white light LEDs.

Attachment:
LEDprobe.jpg
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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Mon 15, 2018 5:59 am 
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Location: Florida
This thread reminds me of my "plug in" flashlight. Years ago I got tired of reaching for my flashlight and finding it with dead batteries so I removed the two D cells and replaced them with a small transformer. It looked a bit strange to have a flashlight with a line cord.

RRM


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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Mon 15, 2018 3:16 pm 
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Location: Mount Pleasant UT 84647 (from Coventry, UK)
A great idea John.


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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Tue 16, 2018 12:15 am 
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Location: Hudson, MA
Very handy :idea:

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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Tue 16, 2018 3:57 am 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Thanks Guys !

Ed---I like your version better ! Being thinner & longer, it would have a better reach, be easier to handle, and fit into tighter areas... Have several of those never-used regulated "wall-warts" since they throw them away at work and plenty of LED's, so may make one like it, also ! You know, you could also put strategically placed LED's inside a favorite chassis as "spotlights" to show it off !

RRM---I can sure understand using an AC power supply for an often-used flashlight to save on battery costs and waste.

Colin---buy yourself a package of those LED's ! You'll eventually find all kinds of uses for them (think of your trailer)...

Eddy---got a chuckle out of your "emoticom" !

John


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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Sat 27, 2018 3:23 am 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 992
Location: Santa Rosa, CA
What a great idea!!!

A friend sent an assortment of white LEDs. There was quite a diiference.
Ended up building three of these 'light probes', one for each bench.
I wanted these to have a longer reach as they will be used for
projects other than radios. I used some 1/4" dia metal tubing,
wired up the LED/resistor then put a piece of heat shrink over
the whole shebang. One end of the heat shrink holds the LED
in place, the other end acts as a strain relief for the cord. Made
them 6" long.

Ran the brightest LEDs at 20mA and the other at 30mA (this was
the warm-light LED).
Steve

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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Jan Sat 27, 2018 6:22 am 
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Joined: Oct Mon 26, 2009 10:02 pm
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Location: Indianapolis, IN
Thanks Steve---good to see others putting the idea to use !

John


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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Mar Wed 07, 2018 2:43 am 
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I did similar. I got an old plastic power cord off some throwaway appliance and installed a white LED and resistor in series on the end of it. My particular use was as a turntable strobe light, you have a disc with a pattern on it, and you can check the speed of a turntable by looking at the circle of marks and if the TT is slow or fast, the strobe effect from the 60 hz will make the pattern appear to move one way or another or stand still if the speed is right on. The traditional TT strobe is a neon bulb but the LED works as well. Plus being a white LED I could use it as you describe to illuminate tight spots.


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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Mar Wed 07, 2018 1:27 pm 
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Joined: Oct Mon 26, 2009 10:02 pm
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Wow, another neat idea---Never even thought of powering the LED's with AC ! And it would be much brighter than neon...

John


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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: Mar Tue 13, 2018 12:43 am 
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Well you certainly get a bit of strobe effect with an LED on AC as they are like a neon versus incandescent. But they don't care, they just set there and rectify away. Actually mine could have been notably brighter but the idea of having it as just a strobe for close work on a turntable led me to be rather conservative with the current through it.


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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: May Fri 11, 2018 9:08 pm 
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Posts: 1959
Location: Thornhill, Ontario
IIRC, the max PIV of LEDs is about 5 volts. So, if you use a higher voltage AC supply with, of course, a dropping resistance, make sure you use a separate diode after the series resistor to sink the reverse voltage pulse. Same goes for LED replacement dial lamps in vintage s/s stereos... I recall some source voltages in these are 8 VAC.
Cheers,
Roger

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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: May Wed 23, 2018 7:27 am 
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Joined: Nov Wed 05, 2014 8:41 pm
Posts: 64
Location: Chilliwack, British Columbia, Canada
Decided to make my own as well, great idea! Quite liking that it is both non-conductive as well as more narrow than even the expensive AAAA penlights I've found.
Body is an old multimeter probe. Powered it with a wall-wart from an Ikea hanging LED light (LEDs long gone) that includes a handy inline switch.
Used the brightest 5mm LED I could locate for cheap on Digi-Key

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 Post subject: Re: Easy homemade LED light "probe"---very handy !
PostPosted: May Wed 23, 2018 12:37 pm 
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Location: Indianapolis, IN
Kaj---glad you like it !

John


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