As I notice a lot of people get confused when they try to build their own schematic. The complexicity in the power input is one of the major problems for the usb power input.So i decide to design a more friendly schematic for those who want to use a 12 power supply only directly.So have a look at this.

Fill in the form and push "Calculate" to get an updated schematic.
link here<----

As you've already realized we love make the things simple...
This is a way i prefer to protect some circuits and varius loads from a reversed battery...

We all make mistakes so a protection is n

This is  a simple circuit based on the famous 555 timer...
With this circuit you can control any load you want but consider first the switching component that the 555 will control....
The n-channel mosfet buz11 can handle 30A and up to 50volts...
You can operate the device connected on the switching component from 5% to 95%.

This circuit is capable of regulating 12V motors and DC light bulbs. No coolrib required for Q1 or D3 if the current does not exceed 2A. If it does, a sufficient coolrib for both the Schottky Diode (D3) and MosFET Q1 is required.
The regulation is obtained via PWM or Pulse Width Modulation. The output pin 3 of the 555 provides square-wave with an adjustable duty-cycle. What that basically means is that the pulse width changes the speed of the motor. The output from the 555 feeds the mosfet via current limiting resistor R2 of 47 ohms. Because the MosFET Q3 only "switches" and is not behaving like a pot, its energy-waste level is negliable, and also provides the motor more coupling at low rpm. The maximum current Q1 can provide (safely) is about 10A.

link to the circuit page<-------

The circuit has been made for the creation of a symmetrical voltage that would come from a single power supply.
The circuit is providing the possibility the possibility of producing a symmetric voltage as required for some applications. This will always come from the existing single power supply of the circuit which is made possible by the use of IC1 L165. The voltage output is symmetrical in nature compared to the normal output.

The following programs calculate the relevant currents and voltages for various switch mode power supplies and display these graphically. Furthermore the programs give suggestions for appropriate choking coils and high frequency transformers.
                                                                                       explore here<---

0-5v led volt meter lm3914