#### Super-Dave

##### New Member

I know from the data sheets that the audio input signal voltage on pin 5 can't exceed the VCC+ voltage (power supply) on pin 3. Since I'm making this for a "car", I'm looking at 14.4 power supply voltage with the engine running. The aftermarket radio to drive this is rated at 60W x 4 using 4ohm.speakers. By my calculations, that is about 15 volts, does that sound right? If this is correct, that'll overload the LM391*, so should I use a resistor inline to attenuate it? How would I calculate that?

And how do I calculate the resistors needed for pins 6, 7 & 8? (Ref Hi, Ref Out & Ref Adj) I know there's an equation on page 8 of the LM3915 datasheet, but I can't wrap my head around it.

"V out = V ref(1 + R2/R1) + I adj R2"

Whaaaaaat????

Whoever's idea to introduce letters to math should be flogged.