Foucault tester - advice needed...

[rochler]

Howdoo folks, I'm planning to build a foucault tester and I'm not sure about the best way to go with the test light - unfortunately I'm very ignorant about electronics so I've got some dumb questions:

I've already got a green super LED (20000 mcd - yikes!) which would probably work fine. It's a 20mA LED with a voltage of 3.6 (max) or 3.4 (average). Would I be correct in assuming that if I powered it with 3 x 1.2 volt NiMH AA's (rechargable) it would run fine without a resistor

Also, is it worthwhile putting a potentiometer in the circuit so I can tone down the light a bit? I"m a bit worried that the LED is far too bright for what I'm using it for - I don't want to go blind hehe...

Lastly, is there some kind folk out there who can do me a little thumbnail circuit diagram (showing polarity etc.) so I've got something to work to? I'm a complete dumbass when it come to hooking things up...

Many thanx, Fred...

[Shawn]

Its a diode, so will only work the right way around, you could use 12v and say 470 Ohm resister if you dont wish to use batteries,

[Garyh]

Hi Fred,
I used a super bright led as well (red), not as bright as yours..and it is plenty bright enough running on 2 rechargables...like sirdystic says with the led its a diode so will only light up with the right polarity........
When you put in a diffuser that cuts down the brightness alot..I used some frosted perspex but to cut the brightness down some more I just stuck a white piece of thin plastic on the perspex..that worked well...not to bright and better difused...
Cheers Gary

[rochler]

Originally Posted by SirDystic

Its a diode, so will only work the right way around, you could use 12v and say 470 Ohm resister if you dont wish to use batteries,

Yep, I'm fairly right on the LED, as you've both said it only works the right way around & you can't really go wrong unless you put too much heat thru it when soldering, or if you apply too much voltage.

I'm cool with using batteries, they're convenient & will last for ages in this application - but did I do my sums right (3 x AA @ 1.2 volt = no resistor?)

Cheers & thanx again

[rochler]

Originally Posted by Garyh

Hi Fred,
I used a super bright led as well (red), not as bright as yours..and it is plenty bright enough running on 2 rechargables...like sirdystic says with the led its a diode so will only light up with the right polarity........
When you put in a diffuser that cuts down the brightness alot..I used some frosted perspex but to cut the brightness down some more I just stuck a white piece of thin plastic on the perspex..that worked well...not to bright and better difused...
Cheers Gary

Thanx mate, I will take your advice & use something to diffuse the LED - the plastic off a milk bottle should do the trick & probably won't need a potentiometer then perhaps? Does that mean you can run a LED on less voltage than the recommended (says min. 3.3 v on the packet)?

Ta, Fred....

[erick (Eric)]

Originally Posted by rochler

....... Does that mean you can run a LED on less voltage than the recommended (says min. 3.3 v on the packet)?......

It's worth a try. I had a red LED I wanted to put into a mount so I could see if motor was on. I also didn't want to draw too much from the batteries that drive it - 3xAA. I had a choice of voltages from inside the unit - I finally went straight across the motor - 1.78 volts. The LED just glows (but will be easily seen in the dark) and is drawing only 0.4mA (!). But I think the specified min voltage for this LED was 1.7 volt, so I'm still above this.

[Satchmo]

Originally Posted by rochler

Thanx mate, I will take your advice & use something to diffuse the LED - the plastic off a milk bottle should do the trick & probably won't need a potentiometer then perhaps? Does that mean you can run a LED on less voltage than the recommended (says min. 3.3 v on the packet)?

Ta, Fred....

Hi Rochler

My advice is use a superbright white LED, you'll get the best view of the surface smoothness than the monochromatic LEDS. Just get the brightest one you can find and leave the room lights on. I find that the eye is much better at judging shadows when the whole visual field is evenly lit, not staring at a bright disc on a black background....

[Shawn]

Sorry to interupt, but what do you use Mark, ?.

[rochler]

Originally Posted by Mark Suchting

Hi Rochler

My advice is use a superbright white LED...

Thanx Mark, I'm going to go with the green one I've already got 'coz I understand that green works particularly well in this type of application. Apparently our eyes are more attuned to the yellow/green part of the spectrum or something....

Cheers, Fred...