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1. In general, I find this the best way to measure the current. Using a DMM in current mode inserts an additional resistance in the circuit which is later removed so the circuit parameters are changed and may no longer be valid when you remove the DMM. The voltage reading mode has a very high...

Re: 5 ohm google: parallel resistors

You are welcome.  Good luck with the exam. If you take care of the current to the LD, you don't have to worry about the voltage.  The 7135 sinks the power above what the LD/resistor will draw. e.g. #1 assume: 4.5V battery source 2.85V across LD/resistor combo (therefore 1.65V across the...

I believe glue is used to allow the crystals/components to be aligned into the "sweet spot" of the LD/beamshaper's output. This allows for the use of LDs from different manufacturer and for variances in LDs.

Unfortunately it's sealed in right now, so I can't really get at it.

The difference is quite noticable in the dot intensity. The beam is very, very faintly visible in total darkness but easy to see if I kick up some dust.

BTW, the power rating for the resistor can be calculated by: P = V * I or P = I^2 * R Example: If I=150mA and R = 19ohms P = 0.15 * 0.15 * 19 = 0.4275 Watts (dissipated in the resistor). Therefore you would need a 1/2 Watt resistor. Paul

Your setup should be something like below.  You will have to use the actual LD if you want to "dial in" pot, otherwise the circuit will not perform as expected when you put the LD back in. Let's start from the beginning.  The 7135s have a range of current outputs, so determine what yours puts...

Where are you measuring the current and how are you measuring it (including DMM setting)? The current out of the 7135 will always be 350 mA. Even if the pot is shunting, say 100mA, then it is dissipating 1 Watt! Very few pots would be rated for that amount of power.

Do you know that you have to put the resistance in parallel with the load to reduce the current? The 7135s are constant current, so putting in a series resistance has no effect. A resistance in paralle will divert some of the 350 (or so) mA away from the LD.

Your pot likely cannot handle the power you are putting through it and is burning out.

I didn't check the current. The board is fairly tight to get at the sense resistor. It's glued now so I don't want to take it apart.

Thanks!  My white on black Dymo cartridge buggered up so I had first used a black on red until I picked up a new cartridge.  The switch is a push button that I took out of something.  It is long enough to rest on the rear of the enclosure.  It is mounted with 2-sided sticky foam tape. My zeroing...

The "freak" is still working fine - it still has its mojo. It's not a stupid question at all. Either resistoring method (series/parallel) should work OK. A series resistor should be a bit more efficient but the value will be a little harder to calculate if you don't know the LD's VI curve...

It may be easier to shunt a little current away from the LD by putting it in parallel with it. A couple of hundred ohms should pull off around 25mA.

Nice pic! I've only seen one worse than that - unfortunately, no pic. It was in a pass through power filter for a shielded room. The filters were on feeders rated 400A @600V. The cap that blew was about the size of my fist. It made a big mess.

I swapped out the dropping resistors on the 200mW red and adjusted the current up from 290mA to about 340mA.  This increased the output from 150mW to 200mW. Here's a pic:

Re: Can I recharge protected CR123a's with an adap I would highly recommend that you treat the Li-ion batteries with care and respect. These things can and will "rapidly vent with flame" (explode) if they are mistreated. It sounds like you are using more than one, so you would need a board to...

Got my board today and quickly finished the assembly. It works very nicely.  I tested a few lasers: 1. Orig batch of Senkat Glowtorch Lasers ("defective" model): ~153mW (Increased Drive Level: now at ~200mW)! 2. DX Lab-type 100mW red: ~125mW 3. DX CR2 30mW Green: ~24mW 4. Cut-down (2xAA to...

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