LED Light Probe - Easy Soldering Project
09-02-2015, 07:35 AM
#21
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Join Date: Oct 2012
Location: San Lorenzo, CA
Posts: 5,361
Originally Posted by Vridar
John, thanks. I will be following this thread with reverence. Please continue to enlighten. You seem to be a patient person we can all learn from. An asset to our forum, for sure.
x2 on this!
09-02-2015, 11:46 AM
#22
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Thread Starter
Join Date: Mar 2015
Location: Denver, CO
Posts: 4,258
Ron,
I mentioned that about 560 ohms would be a good place to start and work down, for a six volt circuit. I have a variable DC supply, so I can mimic what you would have with a six volt DC transformer. I decided to just set it up and show the test.
I had several 100 ohm resistors, so I put 5 of them together, making a 500 ohm series that can be connected at any of the junctions.
(Five 100 ohm resistors)
[ATTACH=CONFIG]529593[/ATTACH]
The basic setup is shown below. I had trouble getting a good exposure of both the parts and the meter face. I opted to show the parts better and inset a closeup of the meter.
NOTE: the meter setting and BE SURE to set the meter for the right range before using it to test.
(LED with 500 ohms)
[ATTACH=CONFIG]529595[/ATTACH]
The meter you use will doubtless be different. Try to correlate these settings to what you have. You want DC milliamps. Since we are trying to adjust for 25 mA of current, I have a 30 mA scale that works well. Pick whatever seems best on your meter.
(Meter Setting)
[ATTACH=CONFIG]529596[/ATTACH]
I worked my down the resistor chain with the following results:
500 ohms = 9 mA
400 ohms = 12 mA
300 ohms = 17 mA
200 ohms = 23 mA
Below is a picture of the last of these tests.
(LED with 200 ohms)
[ATTACH=CONFIG]529597[/ATTACH]
I'd pick the closest standard value to the last test. It doesn't hurt to run the LED slightly below its full rating. If my memory of standard values is correct, you'd have to go up or down a little. Maybe 220 ohms?
I hope this helps.
John
I mentioned that about 560 ohms would be a good place to start and work down, for a six volt circuit. I have a variable DC supply, so I can mimic what you would have with a six volt DC transformer. I decided to just set it up and show the test.
I had several 100 ohm resistors, so I put 5 of them together, making a 500 ohm series that can be connected at any of the junctions.
(Five 100 ohm resistors)
[ATTACH=CONFIG]529593[/ATTACH]
The basic setup is shown below. I had trouble getting a good exposure of both the parts and the meter face. I opted to show the parts better and inset a closeup of the meter.
NOTE: the meter setting and BE SURE to set the meter for the right range before using it to test.
(LED with 500 ohms)
[ATTACH=CONFIG]529595[/ATTACH]
The meter you use will doubtless be different. Try to correlate these settings to what you have. You want DC milliamps. Since we are trying to adjust for 25 mA of current, I have a 30 mA scale that works well. Pick whatever seems best on your meter.
(Meter Setting)
[ATTACH=CONFIG]529596[/ATTACH]
I worked my down the resistor chain with the following results:
500 ohms = 9 mA
400 ohms = 12 mA
300 ohms = 17 mA
200 ohms = 23 mA
Below is a picture of the last of these tests.
(LED with 200 ohms)
[ATTACH=CONFIG]529597[/ATTACH]
I'd pick the closest standard value to the last test. It doesn't hurt to run the LED slightly below its full rating. If my memory of standard values is correct, you'd have to go up or down a little. Maybe 220 ohms?
I hope this helps.
John
09-04-2015, 04:49 AM
#25
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Thread Starter
Join Date: Mar 2015
Location: Denver, CO
Posts: 4,258
This should finish up the LED light probe. I may have to do two posts because of the many pictures.
NOTE: Needed, though I haven't mentioned it yet, is something to insulate around the resistor, inside the tube. There is an electronic supply, commonly called "spaghetti" tubing. I'm showing a piece in the photographs. But a plastic soda straw would do as well. It needs to be the right size to fit OVER the resistor and slip INSIDE the brass tube. Also maybe some kind of boot for the back end of the tube to finish where the wire comes out. I didn't do this, but it might be nice.
Soldering Brass
Soldering will be just a little different, due to the brass tube's greater mass. It will take longer to heat up and to cool down. Soldering will take longer, almost like a slow-motion of the previous soldering. To avoid burned fingers, be sure to allow plenty of time for the tube to cool down.
A second factor is that metal conducts heat very well, There is much more mass than a wire, cross sectionally, and it is a foot in length. For every 2 or 3 degrees you put in with the soldering iron, the tube is probably dissipating away 1 degree into the air. So it takes longer to heat the metal.
Only two solder connections to the tube- one at each end. The one at the back will be easy. The LED end is a little more involved. The LED is physically attached to the tube by its negative (-) lead wire. The case serves as one of the conductors to the LED.
There are two ways I'll suggest to fasten the LED to the end of the brass tube. Any modifications to the brass tube should be done before putting the electronics inside it.
(Two LED mounting methods)
[ATTACH=CONFIG]529698[/ATTACH]
If you decide to drill a small hole, try to make a tiny dent in the tube with some sharp object, and maybe very gentle tapping (very, very) with a hammer. This will help the drill get started without walking around. A Dremel can probably do it. Or a hand drill. A drill press would be ideal. The hole can be very small and brass is a soft metal. This is the method I chose. I think I used a #56 drill, but anything small will work.
(Tube With Small Hole)
[ATTACH=CONFIG]529699[/ATTACH]
The second method of mounting I might suggest is making a little notch in the end to allow the LED wire to get to the outside of the tube for soldering. A small notch could be filed in the edge or perhaps even two careful snips with some good tin shears would do it. All you need is a notch the size of the wire diameter. This will allow the LED to seat against the end of the tube, while the wire passes through to the outside. (see diagram above) Keep the solder at least 1/4 inch from the end of the tube. This will make it easier to get loose, should you ever need to.
I'd do it the second way if I was doing it again. It might be a little easier, I think.
Final LED and resistor soldering
Cut both the wire leads on the resistor to about 3/8 inch. The resistor is, again, good practice dealing with short leads, because it deals with heat well.
NOTE: Small objects you are soldering will tend to stick to the tip.
Figure out some way to hold the resistor down. Lay something across it. Tape it down. Be creative. Anything that works is OK.
(Securing small parts)
[ATTACH=CONFIG]529700[/ATTACH]
Tin the resistor, both ends, pretty much the way you did when the wires were longer.
Then, secure the LED with tape, after cutting the positive (+) lead to about 1/2 inch. Be sure you cut the right one. It is the longer wire, opposite side from the flat spot.
Tin the cut (+) lead of the LED as quickly as possible. Give it a minute to cool.
Finally, secure and tack together the (+) LED wire to one end of the resistor. It make no difference which direction the resistor goes. Again, try to be quick with the heat.
(Final LED and resistor)
[ATTACH=CONFIG]529701[/ATTACH]
The negative LED lead needs to be shaped according to your method of mounting. (See LED Mounting Method illustration above) Bend it to the shape it needs now so that it fits nicely into the tube. It may take a little trial and error. Both methods will need a tinned solder spot either behind the hole or somewhere a short distance from the LED end. Make note for later where you want to tin the brass tube to allow soldering of the negative lead.
(continued in following post)
NOTE: Needed, though I haven't mentioned it yet, is something to insulate around the resistor, inside the tube. There is an electronic supply, commonly called "spaghetti" tubing. I'm showing a piece in the photographs. But a plastic soda straw would do as well. It needs to be the right size to fit OVER the resistor and slip INSIDE the brass tube. Also maybe some kind of boot for the back end of the tube to finish where the wire comes out. I didn't do this, but it might be nice.
Soldering Brass
Soldering will be just a little different, due to the brass tube's greater mass. It will take longer to heat up and to cool down. Soldering will take longer, almost like a slow-motion of the previous soldering. To avoid burned fingers, be sure to allow plenty of time for the tube to cool down.
A second factor is that metal conducts heat very well, There is much more mass than a wire, cross sectionally, and it is a foot in length. For every 2 or 3 degrees you put in with the soldering iron, the tube is probably dissipating away 1 degree into the air. So it takes longer to heat the metal.
Only two solder connections to the tube- one at each end. The one at the back will be easy. The LED end is a little more involved. The LED is physically attached to the tube by its negative (-) lead wire. The case serves as one of the conductors to the LED.
There are two ways I'll suggest to fasten the LED to the end of the brass tube. Any modifications to the brass tube should be done before putting the electronics inside it.
(Two LED mounting methods)
[ATTACH=CONFIG]529698[/ATTACH]
If you decide to drill a small hole, try to make a tiny dent in the tube with some sharp object, and maybe very gentle tapping (very, very) with a hammer. This will help the drill get started without walking around. A Dremel can probably do it. Or a hand drill. A drill press would be ideal. The hole can be very small and brass is a soft metal. This is the method I chose. I think I used a #56 drill, but anything small will work.
(Tube With Small Hole)
[ATTACH=CONFIG]529699[/ATTACH]
The second method of mounting I might suggest is making a little notch in the end to allow the LED wire to get to the outside of the tube for soldering. A small notch could be filed in the edge or perhaps even two careful snips with some good tin shears would do it. All you need is a notch the size of the wire diameter. This will allow the LED to seat against the end of the tube, while the wire passes through to the outside. (see diagram above) Keep the solder at least 1/4 inch from the end of the tube. This will make it easier to get loose, should you ever need to.
I'd do it the second way if I was doing it again. It might be a little easier, I think.
Final LED and resistor soldering
Cut both the wire leads on the resistor to about 3/8 inch. The resistor is, again, good practice dealing with short leads, because it deals with heat well.
NOTE: Small objects you are soldering will tend to stick to the tip.
Figure out some way to hold the resistor down. Lay something across it. Tape it down. Be creative. Anything that works is OK.
(Securing small parts)
[ATTACH=CONFIG]529700[/ATTACH]
Tin the resistor, both ends, pretty much the way you did when the wires were longer.
Then, secure the LED with tape, after cutting the positive (+) lead to about 1/2 inch. Be sure you cut the right one. It is the longer wire, opposite side from the flat spot.
Tin the cut (+) lead of the LED as quickly as possible. Give it a minute to cool.
Finally, secure and tack together the (+) LED wire to one end of the resistor. It make no difference which direction the resistor goes. Again, try to be quick with the heat.
(Final LED and resistor)
[ATTACH=CONFIG]529701[/ATTACH]
The negative LED lead needs to be shaped according to your method of mounting. (See LED Mounting Method illustration above) Bend it to the shape it needs now so that it fits nicely into the tube. It may take a little trial and error. Both methods will need a tinned solder spot either behind the hole or somewhere a short distance from the LED end. Make note for later where you want to tin the brass tube to allow soldering of the negative lead.
(continued in following post)
09-04-2015, 05:11 AM
#26
Super Member
Thread Starter
Join Date: Mar 2015
Location: Denver, CO
Posts: 4,258
Final Assembly
Lay out the parts as shown below to get an idea of how to cut the wires from the transformer. This is why we marked one wire as (+). If you didn't get (+) marked, you need to set up a test again to find out.
Lay the tube and the parts out somewhere. Place the LED beside the tube, located as if it were assembled, i.e. bottom of the LED flush with the end of the tube.
Position the end of the longer (+) wire so that it overlaps the resistor lead by about 1/4 inch. Mark the back of the probe on the wire and strip apart for the length of the tube
Cut the NEGATIVE (-) transformer wire the right length to connect to the back end of the probe. You will need a little separation beyond the end of the tube to connect the negative wire easily. Strip 1/4 inch, twist and tin both wires.
All the parts should look something like this.
(Final parts layout)
[ATTACH=CONFIG]529702[/ATTACH]
Decide if you want anything to slip over the back of the probe, a boot or anything. I didn't do this, but it would be a nice addition. If so, slip it onto the transformer wire now.
Tin the two spots on the brass tube. Solder spots should be 1/8 to 3/16 inch or so. Make one at the rear end of the probe, at the very end of the tube. On the LED end of the tube, make a spot where you think you need it to connect the negative lead.
(Tinning back end)
[ATTACH=CONFIG]529703[/ATTACH]
(Tinning LED end)
[ATTACH=CONFIG]529704[/ATTACH]
Slide the wires into the tube so that the (+) wire protrudes out of the LED end of the tube. To do this, the negative wire will have to be pulled inside the tube for a little way. It will pull back out later.
Slide the spaghetti or soda straw over the (+) wire. This tubing must be long enough to insulate both resistor connections. Don't let the spaghetti get stuck in the tube.
(LED before tubing)
[ATTACH=CONFIG]529705[/ATTACH]
Tack solder the unused resistor lead to the (+) wire. Afterward, slide the spaghetti or soda straw over the resistor, all the way up to the LED. You can wrap a very tiny piece of duct tape around the wire to keep the spaghetti from slipping back.
(Parts ready to put into tube)
[ATTACH=CONFIG]529706[/ATTACH]
Carefully push the LED and resistor, with the insulator fully covering them, into the tube. If you drilled a hole, bending the lead outward at the end helps to thread it through the hole. Work with it until the LED is flush with the end of the tube. Don't solder the negative LED lead yet.
The negative wire should have pulled back out of the brass tube as you pushed the resistor into the tube. Tack solder the negative wire to the back end of the brass tube. Do this end first for practice. Let it cool. If you chose to have a boot for the back of the tube, it should already be on the wire. Slide it onto the brass tube.
(Rear Solder Connection)
[ATTACH=CONFIG]529707[/ATTACH]
Bend flat and tack solder the negative LED lead at the front end of the brass tube. Be as quick as you can with this one. Let it cool.
(Solder LED into tube)
[ATTACH=CONFIG]529708[/ATTACH]
I finished off the light probe with one and a half wraps of white electrical tape, just overlapping the flange at the bottom of the LED.
(White tape for trim)
[ATTACH=CONFIG]529709[/ATTACH]
I think you're done. Plug it in and see if it works.
John
****** Disassembly For Repair ******
Should you need to disassemble the LED light probe, heat the solder that attaches the negative LED lead to the brass tube. Using the soldering iron tip, push the LED lead to the side, then up and away from the tube. Let it cool. Re-heat and carefully (your eyes) tap against the edge of a wastebasket to shake off excess solder. If only a slight solder connection remains, it may usually be broken with gentle but firm pressure on the wire lead from a small tool. Unsolder the negative transformer wire from the back end and guide it inside the tube. Then carefully pull out the LED.
**************************************
Lay out the parts as shown below to get an idea of how to cut the wires from the transformer. This is why we marked one wire as (+). If you didn't get (+) marked, you need to set up a test again to find out.
Lay the tube and the parts out somewhere. Place the LED beside the tube, located as if it were assembled, i.e. bottom of the LED flush with the end of the tube.
Position the end of the longer (+) wire so that it overlaps the resistor lead by about 1/4 inch. Mark the back of the probe on the wire and strip apart for the length of the tube
Cut the NEGATIVE (-) transformer wire the right length to connect to the back end of the probe. You will need a little separation beyond the end of the tube to connect the negative wire easily. Strip 1/4 inch, twist and tin both wires.
All the parts should look something like this.
(Final parts layout)
[ATTACH=CONFIG]529702[/ATTACH]
Decide if you want anything to slip over the back of the probe, a boot or anything. I didn't do this, but it would be a nice addition. If so, slip it onto the transformer wire now.
Tin the two spots on the brass tube. Solder spots should be 1/8 to 3/16 inch or so. Make one at the rear end of the probe, at the very end of the tube. On the LED end of the tube, make a spot where you think you need it to connect the negative lead.
(Tinning back end)
[ATTACH=CONFIG]529703[/ATTACH]
(Tinning LED end)
[ATTACH=CONFIG]529704[/ATTACH]
Slide the wires into the tube so that the (+) wire protrudes out of the LED end of the tube. To do this, the negative wire will have to be pulled inside the tube for a little way. It will pull back out later.
Slide the spaghetti or soda straw over the (+) wire. This tubing must be long enough to insulate both resistor connections. Don't let the spaghetti get stuck in the tube.
(LED before tubing)
[ATTACH=CONFIG]529705[/ATTACH]
Tack solder the unused resistor lead to the (+) wire. Afterward, slide the spaghetti or soda straw over the resistor, all the way up to the LED. You can wrap a very tiny piece of duct tape around the wire to keep the spaghetti from slipping back.
(Parts ready to put into tube)
[ATTACH=CONFIG]529706[/ATTACH]
Carefully push the LED and resistor, with the insulator fully covering them, into the tube. If you drilled a hole, bending the lead outward at the end helps to thread it through the hole. Work with it until the LED is flush with the end of the tube. Don't solder the negative LED lead yet.
The negative wire should have pulled back out of the brass tube as you pushed the resistor into the tube. Tack solder the negative wire to the back end of the brass tube. Do this end first for practice. Let it cool. If you chose to have a boot for the back of the tube, it should already be on the wire. Slide it onto the brass tube.
(Rear Solder Connection)
[ATTACH=CONFIG]529707[/ATTACH]
Bend flat and tack solder the negative LED lead at the front end of the brass tube. Be as quick as you can with this one. Let it cool.
(Solder LED into tube)
[ATTACH=CONFIG]529708[/ATTACH]
I finished off the light probe with one and a half wraps of white electrical tape, just overlapping the flange at the bottom of the LED.
(White tape for trim)
[ATTACH=CONFIG]529709[/ATTACH]
I think you're done. Plug it in and see if it works.
John
****** Disassembly For Repair ******
Should you need to disassemble the LED light probe, heat the solder that attaches the negative LED lead to the brass tube. Using the soldering iron tip, push the LED lead to the side, then up and away from the tube. Let it cool. Re-heat and carefully (your eyes) tap against the edge of a wastebasket to shake off excess solder. If only a slight solder connection remains, it may usually be broken with gentle but firm pressure on the wire lead from a small tool. Unsolder the negative transformer wire from the back end and guide it inside the tube. Then carefully pull out the LED.
**************************************
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