Hello
I'm pretty new to electronics, I am currently designing a fuzz guitar pedal. I plan to use a 2.1 DC jack and a battery snap for PP3 9v battery.
I am concerned about reverse polarity frying my circuit and I have thought of a way to make an LED indicator to warn against reverse polarity.
EDIT to the picture: the diode should go after the LEDs to allow them to light before being redirected.
I have no idea if this will work and would like some feedback please.
Thanks

 

Why not just use a diode in series with one supply lead?
Max.

 

Why not just use a diode in series with one supply lead?
Max.

I did consider just that but I do need an indicator for ease of use. And since it's a guitar pedal a series diode's Vf may alter the results of my project as it is an audio circuit

 

If you need an indicator, place a LED after the diode, if no light, then the polarity is wrong.
If concerned about the diode, place a decoupling cap after it.
Use a Schottky for low Fv.
Max.

 

That seems plausible. Would you need a CLR for the LED still?

 

Not sure what you mean by CLR, the LED would be on all the time unless you come up with a way to clear it, you could always make it high impedance with a high value resistor.
Max.

 

I am concerned about reverse polarity frying my circuit and I have thought of a way to make an LED indicator to warn against reverse polarity.

The circuit you posted won't work. The 1N4001 would prevent the red LED from turning on and would essentially short the battery when reverse connected. You only need one current limiting resistor, assuming the potentially different brightness of the different color LEDs wouldn't be unacceptable.

The suggestion of using a diode in series with the battery connection is the simplest solution; aside from using a battery connection that doesn't allow reverse polarity.

 

To avoid the forward voltage drop of a standard diode, you can use a single P-MOSFET to act as a (near) ideal diode and prevent damage from a reverse 9V battery connection (below).
Its forward drop is just the MOSFET ON resistance times the circuit current.
You might notice that the forward current is a reverse flow through the P-MOSFET, but that's okay, since FETs conduct equally well in either direction when ON.
If the battery input is reverse biased, the P-MOSFET is biased off and does not conduct, blocking any reverse current.

The P-MOSFET can be just about any device with a low enough Rdson to keep the forward voltage drop <100mV (or however low a drop you want).

 

Thanks for your responses guys. Much appreciated.

I think I'll look into the P-MOSFET solution or just do some experimenting (surely no massive harm can be done?).

 

I think I'll look into the P-MOSFET solution or just do some experimenting (surely no massive harm can be done?).

Not if you use a resistor for a load when you do the experimenting.