micro LED lighting project, can't get past step one, could use some assistance

Thread Starter

fbmstar

Joined Dec 23, 2016
8
Hello all,
Well, the short and skinny: i'm building a 1/24 scale trailer model, and have decided to put some tiny led's on it (and also a few micro motors that can be switched on and off). Like the title states, i'm still stuck in the tutorial stage of this, so figured I'd post this in the project forum as i'll likely need more assistance as this progresses.

I decided to start simple as i don't have very much electronics experience, and just hook up 1 LED with a switch. Picture of the schematic is attached. I soldered up the components to a radio shack board, everything seemed to work great. Switched it off, took a little nap, then came back out and the led was on. I flipped the switch and it got a little brighter. So now, the led stays on all the time, and the switch just varies the brightness. I tried rewiring the circuit (the battery and diode are both flipped upside down and the switch is moved between the two). This has the same affect, but the LED is a little less bright when on all the time.

Any ideas on what is wrong? Maybe i applied too much heat to the switch when soldering? Components in the wrong order? The circuit will (hopefully) eventually have about 20 or so lights in series and parallel configurations, and will be very difficult to work on once installed. Any suggestions for more robustness to the circuit?

Attached are pictures of the circuit with the switch on and off after i rewired it. (the relays and black wire are not hooked up to anything currently).

thanks in advance for the help
 

Attachments

markdem

Joined Jul 31, 2013
113
Try taking the switch out of the circuit and just connect the battery directly to the resistor. Does it work? My guess is yes.
So the problem must be with the switch. Have you got a multi meter to test the resistance of the switch?
 

Thread Starter

fbmstar

Joined Dec 23, 2016
8
Thanks for the reply, Mark. I'm getting about 20.2k ohms with the switch in the off position and 0.0 ohms with the switch in the on position. These measurements were taken with the switch still in the circuit (as i'm not sure how well i'll be able to get it out with 5 leads soldered up). I did bypass the switch and it works fine, which is expected i would think as it works fine with the switch as well; the switch just doesn't turn it off fully.

Here's a link to the switch data sheet:

http://datasheet.octopart.com/GT11MCBE-ITT-datasheet-5393594.pdf

I'm not familiar at all with the ratings for the switch, maybe i didn't select the correct one?

thanks again.
 

Thread Starter

fbmstar

Joined Dec 23, 2016
8
and in case you don't want to click on a random link, here's what i believe the the pertinent info on the switch:

CONTACT RATING: 0.4 VA max. @ 20 V AC or DC max.
MECHANICAL & ELECTRICAL LIFE: 40,000 make-and-break cycles at full load.
CONTACT RESISTANCE: Below 50 m Ω typ. initial @ 2-4 V DC, 100 mA.
INSULATION RESISTANCE: 109 Ω min.
DIELECTRIC STRENGTH: 500 Vrms min. @ sea level.
OPERATING TEMPERATURE: –30ºC to 85ºC.
 

markdem

Joined Jul 31, 2013
113
Perfect. So now you know the switch is not turning off.
For the example above non of the ratings will matter. The selection of switch is fine.

When measuring the resistance, did you disconnect the wires from the switch? It can stay in the PCB, just not connected to anything.
Have you got another switch like that? Also, what pins on the switch have you connected the wires to?

Tip for next time, while you are testing, only solder the pins you need. Makes removal easy :)
 

Thread Starter

fbmstar

Joined Dec 23, 2016
8
So, I removed the resistor form the switch, which just leaves a little length of wire still attached to pin 2 on the switch. (basically no effect i would imagine). I'm now getting about 4.78M ohms with the switch off, and 0.0 ohms with it on. I have 10 of these switches. measured two more and am getting 0.L ohms with the switch in the off position. (I guess this is infinite as far as my crappy DMM can see, and seems like what one would ideally want in this application).

just FYI, the switch i purchased is GT11MCBE, which either connects pins 2 and 3 or pins 2 and 1. I'm using pins 1 and 2 only.

thanks for the tip, will certainly keep that in mind as progression is made :)

Still not really sure what the issue is, aside from the fact that i have about 15 more questions regarding this "simple" circuit. Appreciate the help!
 
I suspect that you might have a small solder or solder flux bridge on the PCB. So, I'd clean the flux off and isolate the pads with a razor blade.

I think if you took your "simple circuit" and just wired and tack soldered it without the breadboard it would work. We might be able to see something on the foil side.
 

markdem

Joined Jul 31, 2013
113
Buh humbug. That takes out my theory (I was thinking the switch had short).
I agree with KISS. Just solder the resistor and wire directly to the switch without the PCB. The current has to be bypassing the switch somewhere.
 

Thread Starter

fbmstar

Joined Dec 23, 2016
8
I believe you are 100% correct, that backside looks terrible.

i tried taking a picture of the backside, but my camera won't focus enough to see how terrible it is. Picture attached. You can see the shield of flux around it, but not how much is in between the two active terminals.

Any idea how to clean the flux off? I don't have any rubbing alcohol unfortunately.... i do have chip brushes and acetone. would that work? I'll try a quick air blast first, then just the chip brush. Won't apply any additional chemicals at this time.
 

Attachments

markdem

Joined Jul 31, 2013
113
Just use a screwdriver or knife to scrape in between the pins. It will not look pretty but it will get any flux of hairline joints out of there.
 

Thread Starter

fbmstar

Joined Dec 23, 2016
8
so, i just blasted it with air, and am now getting .425M ohm... apparently that was worse than it was @ 4.78M ohms, right around 10 times worse.

after scraping between the two with a screw driver: about 7.6M ohms.

taking an exacto knife 3 times between them: 3.42M ohm.

not to mention the dial is constantly moving upwards whenever i try to measure it, definitely seems like a fluxxing issue.

took a soldering iron to it to try to clean up all the flux around the perimeter of both leads, getting about 9.0M ohms

tried a micro butane torch (no flame) on it, now getting about 9.67M ohms

any ideas on what kind of resistance i should be looking for?

any ideas on how to get this flux off of there

thanks again fellas!
 

markdem

Joined Jul 31, 2013
113
Hmm, in theory you should be getting O.L when the switch is off as it is just 2 bits of metal with a air gap.
Can you try another switch in your circuit without the PCB and see how you go. This really should just work first time.
 

Thread Starter

fbmstar

Joined Dec 23, 2016
8
Well, the resistance values i was getting were pretty high on the switch, so i tried to connect the resistor up again to try the circuit out a couple of times. After initially soldering the resistor back in, was getting somewhere around 7M ohms. Hooked up the battery and everything seems to be working as it should. Measured the resistance after about 10 on/off cycles and i'm getting 0.L again on the meter!

In conclusion, flux is your friend in the beginning, enemy at the end. Think i'll go pick up some rubbing alcohol and a tootbrush in the AM

thanks again for the help guys. I apologize in advance, but i need to make this single LED circuit into a 20 LED circuit. Will surely be back again for advice:(

thanks again :)
 
Acetone is usually better than rubbing alcohol. A small wire brush also helps. You can get one for a Dremel tool and use a pair of vise grips for the handle.

The flux is easier to get off when it's fresh. Some fluxes are water soluble.

I hope your not using an acid core solder?

I did use warm water and baking soda and an ultrasonic cleaner to remove flux from a commercial test probe. The prep was, ultrasonic in baking soda and warm water, dry and electroless gold plate before it could be used in air at 200 C.

Then again, I worked on electronics where fingerprints were bad. Methanol and Acetone left films that I could measure, but I doubt you can.
 
Your CR2032 battery may not be appropriate.

thanks again for the help guys. I apologize in advance, but i need to make this single LED circuit into a 20 LED circuit. Will surely be back again for advice:(
One thing that you may have to watch out for, is intensity variations between LEDs. You can use the diode test mode on your DMM and sort by Vf. then effectively, use similar Vf's for different sides of your model, so intensity changes won't be noticed.
 

hp1729

Joined Nov 23, 2015
2,304
Hello all,
Well, the short and skinny: i'm building a 1/24 scale trailer model, and have decided to put some tiny led's on it (and also a few micro motors that can be switched on and off). Like the title states, i'm still stuck in the tutorial stage of this, so figured I'd post this in the project forum as i'll likely need more assistance as this progresses.

I decided to start simple as i don't have very much electronics experience, and just hook up 1 LED with a switch. Picture of the schematic is attached. I soldered up the components to a radio shack board, everything seemed to work great. Switched it off, took a little nap, then came back out and the led was on. I flipped the switch and it got a little brighter. So now, the led stays on all the time, and the switch just varies the brightness. I tried rewiring the circuit (the battery and diode are both flipped upside down and the switch is moved between the two). This has the same affect, but the LED is a little less bright when on all the time.

Any ideas on what is wrong? Maybe i applied too much heat to the switch when soldering? Components in the wrong order? The circuit will (hopefully) eventually have about 20 or so lights in series and parallel configurations, and will be very difficult to work on once installed. Any suggestions for more robustness to the circuit?

Attached are pictures of the circuit with the switch on and off after i rewired it. (the relays and black wire are not hooked up to anything currently).

thanks in advance for the help
Cute little LED. Do you have a source, part number and price for that?
 
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