Dropping molex voltage to 9v

[Nicklefrits]

hey guys... my old account was pruned for inactivity so i'm starting new haha. i am not sure if this is the appropriate area for this post, so please move it if you see fit. basicly i am trying to do this: http://www.overclock.net/case-mods-general-discussion/355286-how-make-case-screen-portable-dvd.html .

i have everything except i am lost as far as the whole diode and resistors part is concerned. i am wondering if anyone could give me a crash course in what i am looking for in these two departments as far as radioshack goes... i just got back from there and it was OVERWELMING how many different diodes and resistors they had haha.

What is the exact resistor and what are the exact diodes i need for this project?

Thanks,
Nick

 

[Shadow703793]

Calculate the voltage drop it's not that hard (I will NOT spoon feed you). That should give you the resistor needed.

From the link you posted:

resistors (15k ohm, 12.5k ohm or potentiometer of similar value, 75 ohm)

This is a good place to start: http://www.bcae1.com/resistrs.htm

A few notes: Remember to get a resistor that can handle the power draw.

 

[Nicklefrits]

alright. thanks for the info shadow. however i have come to realize in the tutorial he says that each diode will reduce the current by .7volts... sounds good. now i just need to know what diode out of the 20 they have at radioshack to buy

 

[Nicklefrits]

actually... now that i think of it, i have a few blue led's laying around.... w/ each using 1.4 v shouldnt 2 led's before the screen knock it down to about 9 volts?

 

[RetiredChief]

Just get a 7809 IC a +9 V regulator). It has 3 wires. (1) input - Connect +12 Here. (2) Ground (also is connected to metal tab and is heat sink). (3) output - Regulated +9 V. PS should onl be a couple of bucks, but have not bougth for a while and Radio shack did carry. Wattag on 7809 = 3 Volts times load curret, ie 500 mills x 3 volts = 1.5 Watts should be no problem.

Ref to Diodes. Must be Si and not Ge as Forward voltage drop for Ge is only +0.3 Volts

Added as to Resistors - Looking at them (without calculating) 1/4 W should be fine.

As to leds, yes forward E drop is approx 1.4 V @20 to 30 Mills, They do not like high current like 100 mAmps. They tend to glow just before winking out.

 

[Shadow703793]

^True that. You could use a Vregulator IC, but that's kind of an overkill, no?

 

[jsc]

If all you need to do is drop 12 volts to 9 volts and you need less than 1 amp,
solder four 1N4000 (that's 1N4001 to 1N4007) series diodes in series. Rat Shack has them - or used to, anyway - for 10 for a dollar.