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max time for running a rgb led from small battery

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ghostman11

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hi guys,
does anyone have any idea what the maxium life span of a small 1.5v battery running a low power pic and rgb led would be? yes i know is scant details but a rough guess is all i am after at this point. like would it be days or weeks will do
 
hi guys,
does anyone have any idea what the maxium life span of a small 1.5v battery running a low power pic and rgb led would be? yes i know is scant details but a rough guess is all i am after at this point. like would it be days or weeks will do

hi J,
First point is a 1.5V would not light a LED directly.
 
You will need a boost up power supply (led driver) to make the correct voltage (current) for the LEDs.
A 3V coil cell might be a better choice. They can not produce much current but it will work.
MORE INFORMATION.
 
yeah sorry guys i should have pointed out i was aware i would need some kind of boost circuit, however since i origanaly posted the question i have found a small 4.5v battery that would do the job, however better than that i have been playing with the charger for the wifes electric tooth brush. i would much prefer to do away with the battery and use inductive coupling or whatever its called, i notice you can buy very cheap chargers for nintendo DS that use the same principle so i might get one and have a play with that. i dont need much current or voltage just enough to power small pic and a couple of leds, the leds wont be all on together so i figure if theese things can charge a battery then they can handle a led and small pic
 
So no 1.5V battery. No 4.5V battery.
Will work while in a charger. Will not work when away form a charger.
You will dis-mantel your wife's tooth brush and look at he coils.
OK.....When she lets you back on the internet tell us how that works. lol
 
it did cross my mind to open the wifes charger and have a peek..........but i decided against it so i am going to get one of theese **broken link removed** to have a play with.
the idea is to sit the gadget on top, or to be more precise so you understand why i want to do it this way.... i know someone that makes resin paperweights with all kinds of things in them includeing old electronic componets, we got talking and i thought it would be fun to put a small circuit in one with some leds and a few odd bits of old components and have it flash away etc. but i didnt want wires coming out of it!
if theese battery chargers i have linked too work ok then it should be a nice way to do it, its only a bit of fun and something shiny and pointless to sit on my desk :D

they make theese type of things **broken link removed**
 
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small update. i have made a very small led cube 3x3x3 with 1.8mm red leds, the leds are close close together so i have a nice tight small footprint. its this that i want to attempt to power. looking aroun on you tube and various website that have info on powering leds with inductive power transfer i notice non of them have current limiting resistors on the leds!!!
now unlike a certain other thread on here i DO NOT want to get into arguments on current limiting resistors! actualy i would like to use them with this but wondered why they seem to be always left out with inductive transfer< is this because there isnt enough current to light the led if they are used??? or simply something people just do because they have seen it done that way?
idealy i would like to have enough power transfered so i can use a voltage regulator and current limiting etc, i dont intend to have more than 2-3 of the leds lit at any one time.
 
To save power could you light the leds one at a time, but do it so fast that you would see desired leds on at the same time. This would reduce your current requirements to a little more than 20ma (assuming you are using standard LEDs). You could drop the current requirements even further by driving the LEDs at 10ma and getting less light output. Voltage wise you would need say 3.6v - 4.5v depending on what LDO regulators you wish to use.
 
hi cobra, yep i will probaly light one at a time, output dosnt need to be high as the leds i am using i normaly drive at 10ma and thats plenty for them so i give even drop it a little more. especialy as this is just a fun little gimmick i fancied building :D, i have to admit the whole concept is very intriguing.
 
i want to attempt to power. looking aroun on you tube and various website that have info on powering leds with inductive power transfer i notice non of them have current limiting resistors on the leds!!!
If you get LED current from a voltage source you need a resistor. I know some of the hacks on you tube don't.
"inductive power" By that I think you are talking about switching power supplies that drive LEDs. They are built to drive current not voltage. The supply will increase the voltage until it gets 20mA (or what ever current it is built for). Voltage is of little concern.
 
hi ron. i am talking about the circuits like the ones that charge up tooth brushes without being connected to them. the idea being to run a led cube with no power leads as the cube will be completly encased in resin with the cube suspended in the midle of it.
 
The 'tooth brush charger' can only carry a limited amount of power. I think you can take advantage of that. I would start out with a round wooden stick and wrap 20 turns of magnet wire around it. The output is AC so I would use 4 diodes to make a full wave bridge. Now you should have DC. The little PICs probably should have 2 to 5 volts to run on. Place two red leds, in series, across the + and - points of the full wave bridge with no resistor. The LEDs will act like a Zener diode. If the voltage is 3V the LEDs pull current and try to keep the voltage at that point. Slowly insert the coil into the tooth brush charger. If the LEDs are too bright pull out the coil and reduce the turns. If there is no or little light add 10 more turns. Repeat until you like the results. You might need 100 turns I don't know.

That is just a test. For the real circuit, add the PIC and to keep it from seeing too much voltage add a 5.1 volt zener across the supply. (and a 0.1uf cap) If all the LEDs are off the voltage could get too high so use the 5.1 or 4.7V zener. Or you could use LEDs as zeners.

You need to do more tests. I think if you use one red LED it will cause the supply to drop to 2 volts or under. This will cause the PIC to reset. As the PIC supply approaches 2 volts the PIC's output can not drive much power. The "resistance" of the output pin goes up and this is much like adding a resistor to the LED. So things might be fine. If the voltage is too low or the PIC resets you will need to add a resistor to the LEDs or use two LEDs to increase the voltage.
 
much useful info there ron and a great starting point!!! i have oredered one those cheap DS chargers so the wife can have her tooth brush charger back :D theese little circuits are alot of fun to play with!! i will keep you posted and let you know how it goes. also i have worked out how to do video on the cell phone so if i get it all working i will post a vid :D
 
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