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DIY Laser Torch






It says 250ma's. I find it strange though since he is powering a red LED. And it is being run off of 4 batteries, this driver needs six.
 
Something can't be right..  You can't source 250mA into a standard LED without it blowing up...  And you meter is saying .25mA (250uA).

I use a 10 ohm, 1/2 watt resistor as a dummy load usually.  You can just  measure the voltage across this resistor and the and the current will be I=V/10.  So.. 2.5V would equal .25A.  
 
Gazoo said:
It says 250ma's. I find it strange though since he is powering a red LED. And it is being run off of 4 batteries, this driver needs six.
Click to expand...

Look closer.. he's using the meter for measuring current. The display says "mA". He may have the probe leads in the wrong hole in the meter or something.

One thing's for sure... He's can't really be putting a half watt into that LED.. There's no smoke in the picture.. ;)
 
I guess I am used to my meter because I have mine on the 10 amp scale when measuring current...so 250ma's would show as 0.25ma's. If he is measuring on the 200ma scale then it would show as 25ma's. So I am confused.. ;D

I do like this diagram. IMO it is one of the easiest to follow:

prototype_001_001.jpg
 
Ok, I noticed with 250ma going into the LED, that it was really hot. Then I tried it later with 2 others and fried them. I took 1 resistor out giving me 10 ohms instead of 5 ohms. Now I got a 140-150ma range. This seem about right? Also, when I go to measure the ma output, why will the LED go out completely, then when I remove the voltmeter, it will turn back on? Thanks again! 8-)
 
Sounds like you have your meter in parallel with the output...this is a big no..no. Your meter needs to be in series with the output.
 
Um, can you explain please? That confuses me. A diagram showing where I should measure with my voltmeter would be great!
 
You can use your multimeter (setup to read current) in series with the input.  Connect the positive lead of the meter to the positive lead of your power source, and the negative lead of the meter to the power (positive) input lead of your regulator circuit.
 
Ug, I just burnt some more LEDs trying to figure where to measure the correct way. Anyone got some ideas?
 
troop231 said:
Don't I want to measure after the resistors though? Diagram please?  ;D
Click to expand...

In a series circuit, the current is the same everywhere.


Power Source                    Amp Meter               Regulator Circuit
-------------                  ----------                -----------
|          +|-----------o<-----|+      -|----->o---------|+        |
|           |                  |        |                |         |
|           |                  |        |                |         |
|           |                  |        |                |         |
|           |                  |        |                |         |
|           |                  ----------                |         |
|          -|--------------------------------------------|-        |
-------------                                            -----------
 
Woah that confused me even more lol. Can you just point out in my pics where to measure? That would be fantastic! Thanks!
 
troop231 said:
Ug, I just burnt some more LEDs trying to figure where to measure the correct way. Anyone got some ideas?
Click to expand...

LEDs are not going to work for you unless you use a bunch in parallel..  If you have an extra 10 ohm resistor, you can use it for a dummy load as I mentioned earlier. Then you can just measure the voltage across the dummy load to discern the current.

Also, Gazoo was right.. Your power source is really inadequate for this circuit..
 
Actually measuring between the power source and the circuit is a good idea. The current measured will be the same. I think it was chimo that reminded us of kirchoff's law.

Follow knimrod's instructions...or google it.

how to use a dmm
 
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