"Help!" for: Electronics

[DRG]

So I've read through this entire thread twice, researched on other sites, and picked up some new LEDs... and I'm still just not getting a few things.

1. I've plugged the stats of my new LED setup into an online calculator (http://led.linear1.org/led.wiz) and compared it to the formulas on thatdecade's LED Resistor selection tutorial in this thread and I'm getting wildly different figures. Assuming I want to use one resistor per LED, with a power supply of 6V, an LED forward voltage of 3V, and current of 18mA, the calculator is recommending 180 ohm resistor for each LED. The formula provided by thatdecade gives me 6/.018 = 333.33 ohm. What am I missing here?

2. Running in parallel with a resistor for each LED, is the type of resistor needed effected by the number of LEDs? Say I have 1 LED vs 6 LEDs?

3. Is increasing the size of the battery pack (4AA vs 2AA, for instance) the wrong way to go for increasing the battery life of my setup? I notice that it requires bigger resistors, so is it just getting 'resisted away'? Again, assuming I want to run them in parallel with a resistor for each LED.

4. One of the layouts provided by the calculator suggested 1 ohm resistors. I see they exist, but would they even be necessary?

 

[Gokussj5okazu]

1. Your value of 180 Ohms is correct. The issue you are having with thatdecade's formula is that you are taking the source voltage divided by the current. Take the LED voltage instead. So 3V/18ma = 166.6 Ohms. The nearest common value is 180 Ohms.

2. No, running multiple parallel strands, as long as each LED has it's own resistor, will not affect the required values.

3. Increasing your source voltage will increase your capacity, but increasing your battery pack's current capacity is more effective. If you're using AA's, that means to get 6V you are running 4 in series. If each battery has a capacity of 2500mAH, then that is all your complete pack will have since they are in series. Just for an example, if you're running 6 LEDs at 18mA, that's 108mA total. 2500mAH/108mA would give you a little over 20 Hours run time.

4. YES. I assume you had 3V supply for 3V LEDS. You still need a resistor to limit the current, even if there is no required voltage drop.

 

[DRG]

Gokussj5okazu, thank you so much. These issues have been perplexing me to no end and you explained it in a way even I could understand.

 

[thatdecade]

Goku is close. The voltage drop on the resistor is used in the calculation, not the battery voltage, not the LED voltage. You find the voltage drop on the resistor by subtracting the LED forward voltage value from the battery voltage value.

Example:
2xAA = 3 volts
Generic Red LED has a Forward Voltage of 1.7 volts and a Current of 25mA
Need a resistor value

(3-1.7)/0.025=52 ohms

Plugging these same numbers into the LED wiz calculator, get the same suggested resistor only rounded up to the next common value.
http://led.linear1.org/1led.wiz

That guide I linked in my signature will get you LEDs that light up. To get them as bright as possible, you need to calculate slightly different. I have been meaning to write an updated guide. /time


---------------
I always prefer 3xAA battery packs. Are great for all LED values, wasting very little power with excess voltage (increased battery life)

Using a 3xAA battery pack of 4.5 volts and the other numbers from DRG (3V 18mA LEDs) in the LED Wiz Calculator. You can use a 100 ohm resistor for each LED. Add as many LEDs in parallel like this as you want.

+4.5V

R = 100 ohms R = 100 ohms R = 100 ohms R = 100 ohms

-----------

 

[Silver Gooch]

I am currently working on an Iron Man Mark 7 helmet build and I'm almost done with the fiberglassing stage. The next thing I wanted to do was to install electronics to be able to move the faceplate. Are there any good tutorials to go about that?

 

[SniperWolf]

I'm about ready to install lights and more importantly fans in my helmet. Now I am in way electronic savy. Anyone have a parts list for what fans to use with what batteries and switch. VERY VERY much appreciated.

 

[blackout11c]

I'm about ready to install lights and more importantly fans in my helmet. Now I am in way electronic savy. Anyone have a parts list for what fans to use with what batteries and switch. VERY VERY much appreciated.

All you need for a fan system is -
1x 30mm (approx 1.2 inch) laptop fan
wire (insulated, I prefer multicore copper wire)
a switch (not a tactile or Push-To-Make/Push-To-Break)
9V batteries and snaps seem to work for the fans (as they are rated for 12V)

 

[SniperWolf]

How many batteries would I need to run 2 fans for most of a day? Thanks again.

 

[blackout11c]

How many batteries would I need to run 2 fans for most of a day? Thanks again.

Theoretically, one 9V on each fan would be enough to power them for a day, possibly even two days, depending on how long you run them for.

 

[tabris89]

howdy 405th, im thinking that when i get my armor up and running (still a while off), instead of powering each LED set individually, i was thinking of running the leads for the LED's and such through the undersuit and converging at a central point, maybe the chest. does anyone know of a small light controller kit or something of the like that could allow me to tie them all together? think of a pc fan controller i ask cos i have ideas but not necessarily the know how.

 

[blackout11c]

howdy 405th, im thinking that when i get my armor up and running (still a while off), instead of powering each LED set individually, i was thinking of running the leads for the LED's and such through the undersuit and converging at a central point, maybe the chest. does anyone know of a small light controller kit or something of the like that could allow me to tie them all together? think of a pc fan controller i ask cos i have ideas but not necessarily the know how.

You could link all of the LED's is parallel, with appropriate resistors, and attach them to extra-long connection wires. As you live in aussie, you should be able to buy reels of multicore wire, or even single core wire, from your local Jaycar or Dick Smtih Electronics, if DSE actually sells those. The other alternative, in terms of wire, would be to buy a cheap, several metre long Ethernet cable, or similar, and dissect it.

 

[RobotChicken]

I wouldn't recommend this. I've done full body circuits and you use a lot more wire, have shorter battery life, puts more strain on the wires due to flexing as you move around, introduces more parts (you'll need connectors for electrically joining the parts together, and that in itself introduces another potential failure point), and if any part of the circuit fails then your whole system is down. Separate powering for each armor piece keeps it simple, more durable, and more reliable. Just my 2 cents.

 

[tabris89]

well it was only a thought lol cheers for the input lads it did sound complicated in my head but a 2nd, 3rd, 4th opinion are always helpful

 

[iialucard]

Hey I'm wanting to make a voice amp for a helmet im making and would like to know the easiest way to do so?? thanks for your help

 

[thatdecade]

How many batteries would I need to run 2 fans for most of a day? Thanks again.

Common PC fans pull 250mA, a 9V battery can run this for ~2-3 hours of battery life. One 9v per fan.

If you haven't already bought the fans, you would be better off with a lower voltage than common 12V pc fans. I like the 5V kind, are powerful and can be run on 3xAA (16 hours) or 3xAAA (7 hours).
http://www.ebay.com/sch/i.html?_nkw=5v+fan

instead of powering each LED set individually, i was thinking of running the leads for the LED's and such through the undersuit and converging at a central point, maybe the chest. does anyone know of a small light controller kit or something of the like that could allow me to tie them all together? think of a pc fan controller i ask cos i have ideas but not necessarily the know how.

I agree with RobotChicken. Wires running everywhere make the suit torture to put on and take off without ripping out the wires. Please please please, wire your suit so each armor piece has it's own battery back and wiring.

Having said that. If you really want a single power source for your whole suit, no light controller is needed (unless you want animated lights). Just get a big power pack and run the wiring in parallel.

Use quick disconnects if possible. You can pick these up at your local hardware store.
https://www.sparkfun.com/products/11487

 

[Carpathia]

I'm considering changing this thread from "Help! for: Electronics" to "Ask Thatdecade"

Seriously, every-time I see that this thread is active, I don't even check it if you're the last post, because I know you've answered any question with clarity. Thanks for putting in as much time and effort as you have answering the tons questions people have had!

 

[iialucard]

hey i was just wondering what i will need for a voice amp within my helmet??

 

[FreedNightHawk]

For a voice amp, you'll need a microphone, a pre-amplifier, and an amplifier.

Mics are a dime a dozen pretty much anywhere so I wont bother showing you those. However, for pre-amps, my personal choice would be this: https://www.parts-express.com/pe/showdetl.cfm?partnumber=320-555

As far as a good amplifier, depending on your power needs: https://www.parts-express.com/cat/audio-amplifier-boards-modules/3464.

 

[RobotChicken]

Just noticed Harbor Freight has a 27-LED work lamp for $2.59 - that's a great price for 27 white LEDs.

 

[thatdecade]

I'm considering changing this thread from "Help! for: Electronics" to "Ask Thatdecade"

Seriously, every-time I see that this thread is active, I don't even check it if you're the last post, because I know you've answered any question with clarity. Thanks for putting in as much time and effort as you have answering the tons questions people have had!

Thanks man, I appreciate the appreciation. :$