Driver Using Radio Shack Board

[Sasquach]

I used a breadboard to make this driver but wanted a more permanent driver (as I use the breadboard for other stuff). I also made a test load but that's boring.

Simple Driver using RS board 276-159B. There are actually 2 boards when you buy this (or there was when I bought them 15 yrs ago).

One switch for discharging cap through 1k Ohm (or whatever) Resistor.

One switch for selecting max of 250 mA or 500 mA (by using the 5 Ohm resistor by itself or 2 in parallel).

30 Ohm pot I had lying around

LM317 I had lying around. Pinouts labeled I, O, and A (If you don't know what they mean then nevermind )

Parts are inserted on opposite side of board and soldered where big black dots are.

Pretty easy. I'm going to build this sometime this week.

Side Note: I received my modules from DTR, pressed the diode I found in a 12x DVD burner (knowing it wasn't prob going to burn tape) anyway and created my own LED Now that I think about it I probably LEDed it before I even built the driver. I set my PS to about 3.5 volts and touched the leads. About what I expected but it was a good learning experience. Man this stuff is tiny.


Photo of built driver. Instead of a switch to change max current, I used a jumper (just below the two resistors). With jumper-500mA. Without jumper-250mA.
Sorry for crappy cellphone pic.

[Speedy78]

What does the pot adjust? This is very replicate-able by someone like me who cant seem to figure out how to organize components! Nice job!

[Cyparagon]

It adjusts the current, of course.

I highly recommend tying the unused leg of the pot to the wiper. In the current configuration, if the wiper bounces, it will cause a current spike.

[Speedy78]

Si theres basically a high and low switch and a fine afjustment then?

[Sasquach]

Originally Posted by Cyparagon

It adjusts the current, of course.

I highly recommend tying the unused leg of the pot to the wiper. In the current configuration, if the wiper bounces, it will cause a current spike.

Good point. I thought I had done this.

[Sasquach]

Originally Posted by Speedy78

Si theres basically a high and low switch and a fine afjustment then?

Correct

Adjustment up to the selected current limit.

[Sasquach]

Not sure if this has been covered before but I didn't see it using a search.

If you don't have a 30 Ohm Pot you can change the range of a different pot to make the range smaller.

Say you have a 100 Ohm pot and you want a 50 Ohm pot because it's hard to adjust your driver to get exactly the current you want.

Add a 100 ohm resistor between the wiper and the other non-shorted lead. Now you have a 50 Ohm pot although it's not as linear as the 100 ohm but close. See attached.

You can do this to decrease the value of any pot and you don't have to match the resistance of the pot to change it.

Use this to see how it changes:
Rp- Pot Resistance
R-Resistor

Pot Range = Rp*R/(Rp + R)

So if you use the 100 Ohm pot with a 200 Ohm Resistor then the new range is :

100*200/(100+200)=20000/300= 67 Ohms

Now say you have a 100 ohm pot and you want to change the range to a 20 Ohm pot.

Use this:
R= (Pot Range * Rp) /(Rp - Pot Range)

R=(20 * 100) / (100-20) = 25 Ohms

Add a 25 Ohm resistor and you have a 20 Ohm pot

NOTES:
-This does change the linearity of the pot.
-We are shorting the other two leads so this does not cause the same problems associated with audio devices.
-The New Pot range cannot be greater than the Old pot range unless you can find a resistor with a negative value. If you find one let me know.

Sorry so long.

[Zom-B]

I hooked up an inductor to my ohm meter and it displayed a negative value.