# Infinately ignorant NooBee question.

Discussion in 'The Projects Forum' started by Seax_Smith, Aug 30, 2011.

1. ### Seax_Smith Thread Starter New Member

Nov 15, 2010
13
0
okay, am educating myself slowly (as time allows( on DC stuff).

First sucessfull project was an LED hood for my little 2.5 gallon aquarium. This was a victory for me when I finally made it work, so that should tell you the level I am at.

Batteries, switch, resistors and LEDs had me struggling for a bit - mostly how to arragne the LEDs, which resistors to use and which batteries to use to get me as close to supply demand as possible so I didn't waste battery charge with big resistors and burning off juice the light could actually use later. Tried to maximize the dc current stored in the battery. Dont know if that makes electronics sence or not, but it made sence to me at the time, and I think I am swapping out batteries les often.

Anyhow, want to add something (useless) to it just to learn from doing it.

Is there some way to wire an LED to indicate that the light has been shut off?

Was thinking that I could power the LED from the batteries, put the resistor on the anode, put a diode after the resistor and then ground the diode to the switched power side of the switch. Would the unpowered side of the switch provide (enough?) ground?

Thanks much (if liberal application of the 2x4 of enlightenment is needed, please apply liberally)

2. ### praondevou AAC Fanatic!

Jul 9, 2011
2,936
489
Please put your idea in a circuit diagram and post it. Then we can tell if it's gonna work.

And avoid opening threads called "infinetely ignorant noobee question"

3. ### PatM Active Member

Dec 31, 2010
81
72
Using a big resistor (large value ?) will not burn off juice.
Using a resistor with too small a value could kill your LED because of too large a current.
Using a larger resistor will limit the current to the LED.
You should determine the current needed for the LED and then adjust the resistor value for the current needed to light the LED

4. ### Seax_Smith Thread Starter New Member

Nov 15, 2010
13
0
That's several hours of photoshopping for me becasue I don't have circuit diagraming software.

Will be easier to cut the hood open, test the idea and play with it and eventually reseal the hood.

42? So long and thanks for all the fish.

5. ### praondevou AAC Fanatic!

Jul 9, 2011
2,936
489

Is the attached circuit what you meant?
To know if this works you need to tell us the lamp rating and DC power supply voltage.

Btw, if you happen to have the question to 42, tell me.

File size:
4.1 KB
Views:
18
6. ### iONic AAC Fanatic!

Nov 16, 2007
1,422
68
Read a bit on the SPDT(Single Pole, Double Throw) Switch. In one position the circuit path would be the LED's for the fish tank. Flip the switch off and it turns the Off LED Indicator on.

Heck praondevou's switch is even better. But if you want a challenge try using a LDR(Light Dependent Relay) to switch the indicator LED on! This way you could learn a bit about transistors and LDR's.

Last edited: Aug 30, 2011
7. ### Seax_Smith Thread Starter New Member

Nov 15, 2010
13
0
The question to 42? 8x7 is too Deep of a Thought for me.

Thanks for the Eagle.... will figure out the freeware licence thing at some point - dyslexia makes some things a bit trying.

That diagram is exactly what I was asking.

The "light" itself is 4 strings of 3 LEDs wired in series (series parallel aray).

Used a seven 1.5 volt batteries in series to give me 10.5 volts to supply power to 4(3x 3.3 volt LEDS) so I could use resistors with a really low Ohm value. I know that when I get one fryoide in the 3x string, the other two will fry as well.

8. ### praondevou AAC Fanatic!

Jul 9, 2011
2,936
489
Yes it would be better to use a resistor from the very beginning, otherwise you don't have any control over the LED current.
What is these 3.3V LEDs rated current? My idea is that you had a lamp/light bulb, which have low resistance and wouldn't turn on with the additional LED's current.

Better use a transistor to turn on / off the additional LED. The transistor configuration depends on the LED you will use, it's current/forward voltage drop and the transistor characteristics.

File size:
22.3 KB
Views:
19
9. ### Seax_Smith Thread Starter New Member

Nov 15, 2010
13
0
Diagram is pretty close. Have four strings of 3 LED's totalling 12 LEDs.

Looks like I need to learn about transistors next and the BC457C.

Assuming the J2 is just a simple switch.

No clue what the O1 and O2 is about.

ThInk was that, if I used a supply voltage a little higher then the demand, then I wouldn't loose much battery charge with the low value resistors.

Thanks much for your help. Think I need to educate myself on what a transistor is, what they do and how they do it before I can go any farther with this.

10. ### #12 Expert

Nov 30, 2010
16,676
7,321
The book is The Hitch Hikers Guide to the Galaxy, or something like that. The question is something like, "What is the meaning of life, the universe, and everything?"

11. ### Seax_Smith Thread Starter New Member

Nov 15, 2010
13
0
Douglas Adams..... "super computer" Deep Thought generated the answer to the question "What is the meaning of Life, the Universe and Everything", which was 8x7=42. [pretty sure it was in Restaurant at the End of the Universe.] Thought you would catches the reference to the 'dolphins'.

12. ### #12 Expert

Nov 30, 2010
16,676
7,321
I rely on my signature line often, because...sometimes I'm wrong.

13. ### iONic AAC Fanatic!

Nov 16, 2007
1,422
68
O1 and O2 are actually Q1 and Q2. They are what designates a transistor aside from the actual part number, like BC547...

R1 and R2 are for resistors, T1 is a transformer SW1 is a switch, D1 is for a diode...the list goes on.

I suggest you head on over to the Tutorials section Volume I - DC and read from the beginning.

14. ### praondevou AAC Fanatic!

Jul 9, 2011
2,936
489
I loved his books and especially the hitchhikers books. It's a shame that he died so young.

"Life! Don't talk to me about life"

15. ### Seax_Smith Thread Starter New Member

Nov 15, 2010
13
0
Not positive on the math... other than I know the equation was incorrect. Amazing thing about The Guide is how well he nailed the web, even as the net was just starting to take shape.

Is a Long dark Tea time of the Soul

16. ### Seax_Smith Thread Starter New Member

Nov 15, 2010
13
0
Is how I managed to build the light in the first place.