Let there be light ...


And now we start the study of electronics… 

No, was just a little joke. ;)
Ok, let’s start with a few basics, for example the difference between parallel and series circuits.

Series circuits:


In series circuits the current is identical and the voltages are different. The supply voltage is divided among the individual voltages.


So far so good but what does it mean?
Ok, let’s have a look. 

On the whole string the current is the same, however the voltage is divided by resistors.

The context is simply: the largest resistor has the highest voltage. And good to know: the values of the resistors are added to each other, so you get the whole resistance in the circuit.


Here is an example with LEDs:


With only one resistor several LEDs can be operated. Only the supply voltage has to be greater than the sum of the LEDs forward voltage.

The disadvantage in this circuit is, that if one LED breaks all others will break as well in this whole circuit. So you could say “another one bites the dust”.

Parallel circuits:


In parallel circuits the voltage is identical and the currents are different.
A picture says more than words… ;)



You can see that every string has the same voltage (here the supply voltage), but not the same current. The current depends on the respective resistor.
Another example:


The advantage of the parallel circuit is that each LED has its own series resistor and thereby the current can be adjusted differently. So you can, for example, illuminate LEDs  with different brightness.

And if a LED is broken the others will continue to work.

The disadvantage here is the space requirement, each LED needs its own resistor





Ok, that’s enough of circuit basics, let’s start with the LEDs.



Some informations about LEDs.


LEDs need a minimum voltage to work; which is called forward voltage or simple VF. This voltage is stable and each color has its own VF.

The current ensures the lighting of the LED. A normal LED needs around 8-12mA to work, maximum is 20mA. If they are run with a lower current the lifespan is longer.

A low-current LED works also fine with only 2mA, it just doesn’t shine as bright as others.




For more information of LEDs I’d like to recommend wikipedia.  




Ok, first things first. ;) We determine the VF with a multimeter.

We connect the COM-Port (minus) with the cathode and the voltage-port (plus) with the anode of the LED. The multimeter is then adjusted to the forward voltage, diode symbol.


For the calculation of the resistor we need a law (Ohm’s law)… 
Don’t panic, is all simple math. ;)
 



V: the main power (in this case 5V) , VF: forward voltage from the LED

I: the current that you choose  R: the resistor




Yellow LED:

I = 25mA (my yellow one can up to 30mA) , V = 5V , VF = 2,1V




For the definition of resistors there is a library that defines the values. It's called E-Series.
We look at the E24-Series and take a 120Ω resistor, now we have a current with 24,2mA.



Or if we take two resistors in series the values of them are added to each other as explained earlier.



Red LED:

I = 1mA  (my red is a low-current LED and very bright…)  V = 5V , VF = 1,8V




In the E24-Series this is a 3,3kΩ resistor and after calculating the current will be 0,97mA.






An now some interesting links:
Some calculator...


... and the e-series.




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