Backyard Aquaponics
A place to discuss aquaponics

This thread will be series of simple circuits with hopefully enough theory to get people to understand and build your own widgets.
I will also take requests at any level of difficulty

DIY 12v powerfailure battery powered aerator please

Cool, that sounds fun, I'll do sines basic ones first, then get stuck into that one.
Be patient all, I never have much time !!

Led and current limiting resistor

LEDs like normal diodes conduct in the forward direction (in the direction of the arrow) and block current in the reverse direction.

So if you just applied 5v across the LED without the resistor and if we pretend the LED has ZERO resistance/voltage drop then the current would be Infinity. Infinity current is a lot and the LED would proceed to explode (or something less exciting).

So lets say we were very frugal with our power requirements and only wanted the LED to draw 5 mA. Referring to Ohms Law V=I x R Voltage(V) equals Current(I) times Resistance(R)
What we want to find is R because we already have voltage (5v) and current (5mA)

5v/0.005A = 1000R or 1000 Ohms or 1kOhms

So a 1k Ohm resistor will allow 5mA of current when 5 volts is applied.

It will actually be less than this because the LED has a voltage drop of lets say 1.2v.

So to do this propery: 5v -1.2v = 3.8v

3.8v / 0.005A = 760 Ohms

Any questions ?

computer shops sell batery backups that provide 240 automaticly when the power goes down. most small ones provide around 300w for ten minutes, I guess you might get one or two hours if ya 240v airator is around 30W.
how many W does the average airator consume???

if you do use these as a backup then you must check the battery in the unit ever 6 months. I have seen people complane because there computer crash when the power goes out, but they never checked the condition of the batterys

It isnt hard to upgrade the battery either...

RE: LED's and resistors.

I was under the impression that it shouldnt matter which side the resistor goes on.

I just tested it and actually got a quite satisfying explosion as the LED fell over.

Which also means I have to undo a stack of soldering I just finished.

Now I'm even more confused than I thought I was before.

What voltage and resistor did you use?

4.5 volts , 330 ohm resistor

Bullwinkle it doesnt matter which side of the LED the resistor goes.

What its the current rating of the LED ?
Did you have thE LED backwards ?
Normal diodes are good at blocking, however LEDs typically can't handle very high voltages in the reverse direction, that number is also in the datasheet for the part. Make sure you have the datasheet Send me a link and I can point out the bits you need to take notice of.

Did you accidentally bypass the resistor and apply voltage directly across the LED ?

MOSFET switching on LED with current limiting resistor.

The LED current is calculated as before, resistance of the MOSFET is generally negligible.
There are some important specifications of the FET (MOSFET) that need to be considered before selecting one. I just realised we might need a separate post about FETs.

By applying a voltage to the FET Gate - the horizontal pin labelled "Signal"
the FET can be turned on. Making the voltage on the Gate go to 0v will turn the FET off.

Its just a switch.

The resistor between the gate and ground (0v) makes sure the FET doesn't turn on by itself, the radiation from a phone, or other electrical device, even the radio station can turn on the FET if your circuit isn't driving the Gate signal High or Low. Also the FET can be half on and half off, acting like a resistor and destroying itself.

Questions ?

Any feedback would be great. I don't really want to spend all this time if no one really cares.
But am very happy to if people are genuinely interested.

Let me know

Are you happy with this gorotsuki69 ?

I think I must have touched it to somewhere with the full 5 volts.

I tested it again because I quite liked the sound it made, andit didnt happen.

Thats the problem with being a beginner, you have no idea if the fault is with your knowledge or with the circuit.

It can have you chasing your tail.

as for the data sheet, the LED's came in an assorted colour pack, home sealed with no label and with resistors included, so I have no idea

But now have one data. In some arrangement, they go pop at 4.5 volts

That'll happen I quite enjoyed letting the smoke out of things at uni.
If you whack several volts across a normal rectifier diode (black one) it will look like a LED. But only for about 1 second