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Old 01-22-2008, 08:13 PM #1
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Default My First Post!! 100 ohm pot question

How about a stupid question for my first post!!!!

I've read and read but cant find the answer.

Does it matter what 100 ohm pot I get for the Daedal driver? single turn? how many watt? etc. *If someone has a part number that would be great. I want the smaller box type board mount style.

My electronics supply store has no 100 ohm in stock so they will need to order it in for me. I may as well order exactly what I need.

Making a box one first before I try and stuff it all into a flashlight!!!

Thanks


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Old 01-22-2008, 08:21 PM #2
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Default Re: Mt First Post!! 100 ohm pot question

Hi and Welcome!

You really don't need anything huge. I've been successfully using a 1/4w single turn 20ohm trimmer pot, but it IS on a ceramic substrate, so it has good heat dissapation comparatively.

It also depends on your duty cycle (how long you expect to keep it on continuously for vs. off time). My duty cycle is pretty low usually - Seldom do I have it on for longer than 30 seconds or so - and in all that time I have never felt any appreciable warmth generate on the pot. The diode, the LM317 - yes, toasty. The pot? No.

Do, however, be sure you heat sink the laser diode - the head of the Aixiz module is good for low duty cycle use - and be sure the diode is FLUSH MOUNTED for maximum heat transfer efficiency.

Also- with your pot - be sure to use another 4 ohm resistor in series so you can't accidentally reduce the resistance to below the minimum - thereby frying the beloved laser diode (experience talking here). If you're using a Senkat diode (highly recommended) you probably don't want to pump more than 290mA into it for any significant period of time. I usually run mine around 250mA and it burns like crazy!

Good luck & have fun!

Dave

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Old 01-22-2008, 08:30 PM #3
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Default Re: My First Post!! 100 ohm pot question

I'll be making the driver circuit with the 6V, LM317, 100 ohm pot, 4 ohm resistor, 1N4001 diode and 47uF 35V cap soldered to the StoneTek/ Aixiz combo
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Old 01-22-2008, 09:26 PM #4
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Default Re: My First Post!! 100 ohm pot question

Welcome! DDL has a couple of links to pots on this 1st page of his Driver thread:
http://www.laserpointerforums.com/fo...num=1185701612
One link is to Digikey and the other is to Radio Shack. Hope that helps...
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Old 01-22-2008, 09:34 PM #5
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Default Re: My First Post!! 100 ohm pot question

Actually 100 ohm is quite too much... you will never need 100 omhs, less ohms in the pot means more precise adjustment, for a stonetek diode 20ohms would be nice maybe a little more if you want like 50ohms but IMO 20 is enough, with a 4ohms in series. since the most common current ran through these diodes is 250ma you'll want a total of 5 ohms, make sure to check everything with a multimeter
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Old 01-22-2008, 09:41 PM #6
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Default Re: My First Post!! 100 ohm pot question

I absolutely agree, a 100ohm is overkill. In fact if you plan to use the same diode, SenKat's for example, a pot is not needed. Just solder a 5 ohm 1/2 watt resistor between the output and adj. and you are good to go.

Kenneth_v,
Welcome to the forum. No question is a stupid question. One other note, you can get by with a 10uf 16 volt capacitor. They are much smaller and provide ample protection against voltage spikes. 47uf is overkill.
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Old 01-22-2008, 10:47 PM #7
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Default Re: My First Post!! 100 ohm pot question

10, 100, 51... I'd go for a 25 myself :-)


now if you want somethig that's good for blu-ray too...
a xx-ohm fixed with a yy-ohm trimmer

it depends on your driver circuitry of course!

another good parts source is Newark
go to Passives / Potentiometers/ Potentiometers-rotary
and figger it out from there.

if I remember correctly they don't have a minimum order...

fixed resistors are about 9c to 12c, depending... you might have to order 10 each depending in the item - that's a whopping $1.20 for the 12-centers.

they have 30 varieties of 15-ohm pots ranging from about 80c to $4

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Old 01-22-2008, 11:21 PM #8
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Default Re: My First Post!! 100 ohm pot question

Here's all the things you need to buy from radioshack. I included both the 25 ohm rheostat and the 1k ohm pot so you can choose between them.
The rheostat is huge but it's more accurate, the 1k ohm pot is small, but it's difficult to adjust.
The total for parts with the rheostat is $11.44
The total with the pot is $10.14
Just choose one ;D sorry it's a little messed up, that's just how it shows up when I attach it.
[smiley=smiley_down.gif]
[smiley=smiley_down.gif]
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Old 01-22-2008, 11:52 PM #9
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Default Re: My First Post!! 100 ohm pot question

Thank you all for the responses.

I post a few more times as my build goes along im sure!!

I'm sure glad I found this site. From reading throught the forums, it looks like lots of great helpful people here.

Thanks again
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Old 01-23-2008, 01:43 PM #10
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Default Re: My First Post!! 100 ohm pot question

Quote:
Originally Posted by Kenneth_v
Thank you all for the responses.

I post a few more times as my build goes along im sure!!

I'm sure glad I found this site. *From reading throught the forums, it looks like lots of great helpful people here.

Thanks again
If you want the small PCB mount 100 ohm trimmers, I usually use the 25 turn ones (multi - turn). I've found them at Willy's electronics (local) as well as Fry's Electronics (chain). I bought a bag of the ones recommended from Digi-key, but I don't like the form factor. I'll post brand model if I can find the package at home, but they are more like these:

http://www.allelectronics.com/cgi-bi..._100_OHM_.html

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Old 01-23-2008, 04:23 PM #11
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Default Re: My First Post!! 100 ohm pot question

Since I am making a box version, I have lots of room to work with. Next project will be the flashlight version.

The reason for making my laser is for teaching various ways that the power of light energy can be used to ignite a fire. (focused sunlight with the polished bottom of a pop can, magifying glass, etc and finishing with the laser) There will be a bundle of wooden matches hidden in the centre of the tinder so I just have to ignite the matches. Cheating a bit but looks impressive.

I will have a fairly short duty cycle, enough to light the matches but I would like to do it from as far away as possible. I will add a pot as I would like to be able to fine tune the output for better performance over a distance with a shorter duty period.

Any suggestions for improvements in the design for this purpose??

Ken
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Old 01-23-2008, 04:40 PM #12
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Default Re: My First Post!! 100 ohm pot question

Quote:
Originally Posted by Kenneth_v
I will have a fairly short duty cycle, enough to light the matches but I would like to do it from as far away as possible. *I will add a pot as I would like to be able to fine tune the output for better performance over a distance with a shorter duty period.

Any suggestions for improvements in the design for this purpose??

Ken
What I am going to do in my next red burner, is make a "turbo" switch so it will run at ~150 mA normally, then when the momentary switch is pushed, will bump the current up to ~300. I accidentally made something like this when a loose connection would intermittently bypass the lm317, and bump up to 396 mA. It cut black plastic like a hot knife. But I wouldn't recommend that current for decent life of the LD.
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