Hey, good news: I am almost completely done with allocating the parts for my build. I need answers to two more questions and then I should be squared away...
1.) LEDs - I am attempting to preform the LED mod to my PSone screen. I am trying to find white LEDs that will be used for the backlight; however, I am having difficulty knowing which resistors to get for them. I found these on radioshack.com: http://www.radioshack.com/product/index ... =techSpecs. I tried to calculate the proper resistor i'd need for 4 wired in a series but became confused . Can someone tell me what resistor i need to use here with these? Would the LEDs draw their power from the 12v line or the 3.3v line?
2.) Fans - I have decided to go with a small fan in my portable. My main concern about using a fan is that it will draw too much power from the battery. I have decided to go with a 7.4v, 4800mAH battery to conserve weight and size of the portable overall. I plan to use a combination of small heatsinks and a fan. How much charge does the fan draw from the battery over a period of time? I want to be able to play the portable for at least 2.5 to 3 hours. The size of the fan is something I have not identified yet; however I am thinking of one between 40mm and 60mm in diameter (here is an example: http://www.newegg.com/Product/Product.a ... 6811999701) (is that an appropriate size? has anyone used a different size fan?). Granted the power of a fan this size, would I need to upgrade to a higher capacity of say 6000mAH to run the portable for 3 hours?
Any recommendations or advice regarding all this shiznit would be greatly appreciated...
try a 10 ohm (that's an estimate) resistor for the LEDs. a small fan should take no more than 150ma, get a small one (i used a 25mm i think). the whole portable shouldn't draw more than 1-1.3A (a very rough estimate) so you're battery should last at least around 4 hours. also you need 3mm, not 5mm LEDs. get the highest mcd and viewing angle (viewing angle is important) you can find. ebay is a good source for plenty of those at a much cheaper price than those radioshack ones. i just power my LEDs straight from the battery voltage and tehy work fine
Last edited by daguuy on Thu Mar 09, 2006 9:03 pm, edited 1 time in total.
i would use more than a 10 ohm resistor, maybe 20. its up to you a little. the higer the resistamce, the dimmer the lights, but the less power they draw.
i dont think you can wire 4 in series, unless you have LEDs that run off less than 2V. im not sure how others do it... but if you put 2 in series and 2 in parallel on the 7.2V line, then you would have 3.6V per led. thight might be too much... well lets go with it anyways. so lets say you have that, and each LED needs maybe 80mA at most (Random guess. probably a bit high) so you need 160mA.
V = IR
7.2 = 45
----
.16
so that quick calculation says 45 ohms. ultimately its comes down to "is my screen bright enough, or do i need a smaller resistor?". but with a 10 ohm resistor across the 7.2v line, you are drawing 7.2/10 = 720mA. thats like 6 fans.
the fan in that picture is probably too big. draw its dimensions on a piece of paper if you dont know exactly how big it is. i dunno. ive seen 20 or 25mm fans that would work sweet in a portable. just look around for them.
that particular fan also draws 190mA. i have one that draws 60mA and is the same size, so you can definitely do better. (mines from a PS2)
hm. it depends. assuming you can keep the exact power comsumption of the LEDs the same (which would be hard if youre chaging the voltages around), then it would be more efficient before the converter. for ovbious reasons
overall, i wouldnt worry about it. probably negligible.
I have seen a 30mm fan before, but i am concerned that with small heatsinks (probably RAM heatsinks), not enough heat will be dissappated. I just don't want my chips to melt....
In regards to the LEDs: i guess i'll have to take back the 5mm ones i got tonight. 3mm wide angles was what daguuy suggested, so i guess i'll go with them. I just am confused as to the best configuration for the LED mod, since i want to have an more efficient lighting source than the PSone screen currently has.
What would be my best course of action in regards to the LED mod and the circuitry?
yeah, 5mm's just dont fit into the place where they need to go. you hafta get the 3's. one at each corner, all facing the same direction (either clockwise or counterclockwise) is probably the best way to do it.
that fan looks pretty ok. its a 12v fan, so it will run slower off 7.2v... or possibly not at all.
daguuy, sorry if this sounds redundant but i am thinking about ordering the battery (which is expensive...). You said given I use this 5mm fan with the LED mod that I would get at least 4 hours? Is this based off of mathmatical proof or is it speculation (if i sound critical, i really don't mean it. I just want to make sure the 4800mAH battery is the right one to buy...)
4800mah is great. i expect to get around 4 hors with my 4200mah battery. the 3.3v line with dc-dc convetor takes around 700ma, 12v takes 100-300ma (some games might take 500ma), and the screen takes around 350ma when led modded. that's around 1.1-1.3A. that means a 4800mah battery should give somewhere around 3.5-4.5 hours
Awsome. Thanks for all your clarification and guidance. I honestly was new to all of this maybe 3 weeks ago and all of you brought me up to speed quite quickly.
I have to go to Washington DC tommorrow for a field trip of sorts, but afterward I will order the battery. However, when i get home, my step down converter will have arrived from TI .
umm just wondering but which battery is he getting?(im trying to make a n64p too and looking for a good battery)
EDIT:oh wait never mind i didnt read it very well... sorry about that
Good news again: i ordered the battery and the charger to go with it. They should arrive sometime next week.
In the meantime, i would like to get everything else done so when i have the battery, all i have to do is make the appropriate connections. One of those connections is the LED mod; which doesn't seem to hard in practice, but its hard to find a good deal on wide angle 3mm white bulbs.
Thats 50 LEDs for 14 bucks. I only need at most around 6 (in case i want more or just want spares just in case i blow a couple). I don't want to pay 14 bucks since the battery+charger+fan+equipment has already set me back a good $100.
Does anyone know where i can order the same kind of LEDs where i can specify how many i want so i don't have to pay 14 bucks?
digikey is a really good place to get parts from, and they ship real fast. but if you order less than $25 dollars worth of stuff, they charge you an extra $6 or something.
the LEDS is got from there were lik $3 each. i also found surface mount resistors and capaitors for 4 cents each... guess who ordered 500 resistors and capacitors
. Can someone tell me what resistor i need to use here with these? Would the LEDs draw their power from the 12v line or the 3.3v line?
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