led lamp

[audioguru]

I've never seen nor heard of that BC-thingy, and in Australia?
Also, he might endup with a ferrite AM radio loopstick. :(

[ante]

Sure! On a day with your stupid hat on, anything is possible! ;D ;D

[iceman302]

hey audioguru forgot to ask lat time wat type of capacitors work best for that circuit u gave me?

and i can't find any 7660 IC's anywhere. is there any alternative circuit or parts that i could use. i'm also going on a long shot to try and find the 7660 but i'm just asking if theres an alternative just in case i can't get the parts

[audioguru]

hey audioguru forgot to ask last time what type of capacitors work best for that circuit u gave me?

Electrolytic capacitors with 10V, 16V, 25V, 35V or 50V ratings are fine.

and i can't find any 7660 IC's anywhere. is there any alternative circuit or parts that i could use. i'm also going on a long shot to try and find the 7660 but i'm just asking if theres an alternative

Go to www.farnell.com and click on your country's flag. They have their part number 408554 for ICL7660CPA made by INTERSIL for AU$2.55 each and they are in stock today. They deliver by Parcel Post or by courier if their warehouse is too far from you.

[iceman302]

oh ok thanx m8
if i have any more problems then i'll post ;)

[iceman302]

sorry to be a bother u again audioguru
but i was just wondering, if i wanted say 8 led's instead of 4 and run it on 4 aa batteries how would i go about altering the circuit u gave me to do this?
because i'm afraid that four will not be bright enough?
and i figure that it maybe a bit easier to do two 8 led circuit then try and connect 4 of the circuits u gave me.
thanx for the help so far its been great.

[audioguru]

Iceman,
Five days ago you said: "the project states that for every 4 led's there must be 2 aa batteries. [where a set is 4 led's to 2 aa's] this is a requirement that must be meet."

Therefore I designed a voltage stepup circuit for you since the LEDs need more voltage than two cells can supply.

Now you changed everything by doubling the battery's voltage to 6V.
The LEDs need only about 3.3V. The current through each one must be limited to 25mA.
It is simple to design a current-limiter for each LED by using a resistor in series with each one, just use Ohm's Law. The resistor will have 6-3.3=2.7V across it. Ohm's Law says its value is 2.7V/25mA= 108 ohms. 120 ohms is the nearest standard value and will result in 2.7V/120= 22.5mA through it and its LED in series with it.
Eight LEDs with their own 120 ohm resistor will draw 180mA and four AA alkaline cells in series will last about 10 hours. 

[iceman302]

ok thanx audioguru,
sorry bout the trouble i really should be a lot clearer when i post.
;)

[iceman302]

hey it me again :), sorry to disturb every1.
ok i just got the parts in and i was wondering if the following configuration is correct before i put it together. note that the resistors are 120 ohm's.
i just need an ok and i'll be on my way. sorry bout all the confusion and all aduioguru.

:-\ :-\ :-\ :-\

[audioguru]

Hi Iceman,
What are you doing? ???
You don't need the LMC7660 voltage step-up ICs when you use more than 3V. The LMC7660's, the LEDs and maybe even the battery would blow-up in your 12V circuit. The resistors would smoke too.

You don't even need 12V from 8 AA cells when the 120 ohm resistors were calculated for only 6V from only 4 AA cells. 4 of the battery cells would be wasted. Use Ohm's Law to calculate that 12V would create a current of 72.5mA through the LEDs but their absolute max current rating is only about 30mA.
Figure how much current would try to flow if you doubled the 12V to 24V!

I have modified your circuit to show how easy it is to power 3.3V LEDs from a 6V battery. If you leave it turned on continuously, the 6V battery will last for 15 hours if you use 4 Energizer AA alkaline cells.

[iceman302]

ok i get it but i have to stick with the restriction of "for every four led's i must have 2aa batteries".this could either be 4aa's to eight led's or 8aa's for 16 led's. it's a little hard to explain but thats what my brief states.
i guess now u can understand why i need help ???

but i get the gist of wat u r saying and again sorry for all the confusion. but this restriction is a bit part in the marking so i want to stick to it. i really don't care if the other batteries are wasted as long as the lamp is bright as possible.

thats for the help so far its been a god send

[audioguru]

I designed two circuits for you that had 2 AA battery cells for every 4 lighted LEDs.

I hope you are correct by using 8 AA battery cells with a total of 16 LEDs.
This circuit is simple and its battery will last a long time.