so many resistors!

Includes but not limited to: SNES, Genesis, Sega CD, PlayStation 1, Nintendo 64, Dreamcast, Game Gear and I guess the Virtual Boy.

Moderator: Moderators

daguuy
Portablizer
Posts: 3666
Joined: Fri Apr 01, 2005 7:09 pm
Location: missoura

so many resistors!

Post by daguuy »

i looked for a 3 0hm resistor on digikey to add to a 7805 to get 3.3v. i searched for "resistor" and scrolled down to the resistors and there are so many different kinds i don't know what i need :? . which kind should i get?
nos_slived
Higher Idiot
Posts: 3476
Joined: Mon Mar 21, 2005 6:32 pm
Location: Burnaby, BC, Canada
Contact:

Post by nos_slived »

Digikey has a $25 minimum, so you're better off going to a small electronics store near you.
Image
daguuy
Portablizer
Posts: 3666
Joined: Fri Apr 01, 2005 7:09 pm
Location: missoura

Post by daguuy »

good point. in didn't know about that
rawls
Posts: 137
Joined: Thu Apr 07, 2005 11:34 am

Post by rawls »

Digikey doesn't have a $25 minimum. They just add a $5 handling fee to any order under $25. If you are just getting a resistor, though, then just go to Radio Shat.
daguuy
Portablizer
Posts: 3666
Joined: Fri Apr 01, 2005 7:09 pm
Location: missoura

Post by daguuy »

i'm getting either 2 1amp 7805s and 2 resistors or 1 1.5amp 7805 and 1 resistor
marksalot06
Posts: 17
Joined: Sat May 28, 2005 8:15 pm

Post by marksalot06 »

what do you need a resistor for?
daguuy
Portablizer
Posts: 3666
Joined: Fri Apr 01, 2005 7:09 pm
Location: missoura

Post by daguuy »

getting 3.3v. i saw a diagram that i want to use on triton's site: http://www.gannon.tk/~triton/concepts.htm
Turbo Tax 1.0
Portablizer Extraordinaire
Posts: 4773
Joined: Wed Mar 30, 2005 6:19 pm
Location: Delaware, no sales tax
Contact:

Post by Turbo Tax 1.0 »

that diagram has the battery going to output i think it should be the other way around
when life gives you lemons make flux
Image
snesp mk4
daguuy
Portablizer
Posts: 3666
Joined: Fri Apr 01, 2005 7:09 pm
Location: missoura

Post by daguuy »

yeah i'll have to check that out
superdeformed
Portablizer Extraordinaire
Posts: 298
Joined: Thu Mar 03, 2005 4:45 pm

Post by superdeformed »

I don't think using a 3 ohm resistor will work, as the N64 won't be able to pull enough current through it. One way using resistor's and 7805's that I tried was posted by gamelver (I think). It was 2 7805's in parallel (to handle the current) and one, 1 ohm 10 watt resistor in line to the 3.3v line. A 2 ohm resistor might also work but remember that everything is going to get extremely hot, so you will likely need a heatsink on it. If you have the money and patience, a linear regulator will be much more efficient.
rawls
Posts: 137
Joined: Thu Apr 07, 2005 11:34 am

Post by rawls »

Yeah, just adding a resistor to the output expects a certain current through the resistor to get the required voltage and will be very innefficient. Using a regulator will be a better option, or you could add a 3.3V zener diode to regulate the voltage. The zener will be almost as cheap as the resistor and more accurate and efficient (though not as good as a regulator).
daguuy
Portablizer
Posts: 3666
Joined: Fri Apr 01, 2005 7:09 pm
Location: missoura

Post by daguuy »

what kind of regulator are you talking about? if it's an adjustable one, how would i adjust it to get the right voltage?
rawls
Posts: 137
Joined: Thu Apr 07, 2005 11:34 am

Post by rawls »

A very efficient regulator is the LM651 (my post on this page talks about it). Linear 3.3V regulators exist but I just checked on Digikey and they're all out (at least of those which can handle >1A and don't have to be bought in bulk).

A zener diode is just a diode that you put in the opposite direction of current and it lets roughly the voltage it is rated for through. They are a very simple way to regulate voltage.
nos_slived
Higher Idiot
Posts: 3476
Joined: Mon Mar 21, 2005 6:32 pm
Location: Burnaby, BC, Canada
Contact:

Post by nos_slived »

You must use different zeners than me, because all through electronics, all the zeners we used would let all the voltage through, as long as there was enough to open it.
Image
rawls
Posts: 137
Joined: Thu Apr 07, 2005 11:34 am

Post by rawls »

You have to set the circuit up correctly (the way I worded my last post was misleading). The zener maintains a (relatively) constant voltage across it, so you have to set it up to ground to maintain your current. The circuit looks like this (using a 5V regulated supply and assuming maybe 1A load):

Image

If you use a regulated load, this will be a decent regulator. If you use an unregulated one, then the voltage will shift around depending on the input voltage. Also, this depends on a constant current; as the current shifts the Vout will change as well. I don't know much of what the 3.3V supply for the N64 is used for, but if the current changes a bunch, you should either use the zener with transistor emitter follower, or just a voltage regulator (the latter being preferable).
Post Reply