Reading PWM signal with Arduino?

Greetings all. Im a Car Audio buff and i need to get more voltage out of the alternator. The Alternator get a signal from the BCM to control the output voltage and i would like to extract a sample of this signal and duplicate it only with outputs at my control. Can this be done?

You can't directly read PWM but you can filter it with a [u]low-pass filter[/u] to get varying DC that you can read with an Arduino analog input.

If it's 12V you'll need a [u]voltage divider[/u] knock the voltage down to 5V. And, it would be a good idea to add a [u]protection diode[/u] in case the voltage (into the voltage divider) goes over 12V.

Also if it's 12V you'll probably need a driver circuit to boost the "new" (5V) PWM out of the Arduino.

The voltage on the wire fluctuates from 8.1v (12.8v out) to 9.3(14.7 out)

PWM signal of suitable voltage level can easily be read by an Arduino.

Duty cycle, voltages and frequency are key.

If all you really want to do is duplicate the signal, that’s better done in hardware, but you really have to tell what you want to duplicate it to, and why it has to be duplicated in the first place.

Ya I was hoping the Arduino could read it and if it can if there is a reference that can help me do this.

Lots of examples on google.

As said, expected signal matters. A 1 Hz signal would get a very different approach than a 1 MHz signal, and a 1 kHz signal likely yet a different approach.

If voltages are out of range for the Arduino external hardware is needed to condition the signal. What hardware... again depends on the signal itself.

So keep those things in mind when searching for suitable examples.

Kickergt:
Greetings all. Im a Car Audio buff and i need to get more voltage out of the alternator.

How much more voltage and why?

The alternator outputs the voltage it does because that is the correct voltage to charge the battery. Lead acid batteries have a tight window of voltage for charging them, go too high and they boil dry, too low and the don’t charge. Not only that but the vehicle electrics are designed around the voltage the battery and alternator are set up for.

If you want a higher voltage for powering in car audio then either use a boost converter to get the higher voltage, or, if your skills are up to the job, install a second alternator and battery system from a lorry or other commercial vehicle with a 24V nominal output.

PerryBebbington:
How much more voltage and why?

The alternator outputs the voltage it does because that is the correct voltage to charge the battery. Lead acid batteries have a tight window of voltage for charging them, go too high and they boil dry, too low and the don’t charge. Not only that but the vehicle electrics are designed around the voltage the battery and alternator are set up for.

If you want a higher voltage for powering in car audio then either use a boost converter to get the higher voltage, or, if your skills are up to the job, install a second alternator and battery system from a lorry or other commercial vehicle with a 24V nominal output.

I’m guessing the amp etc are in the boot or at least a “fair distance” (as far as 12v dc is concerned) from the battery and because of the large instantaneous current sometimes required is causing big problems with the voltage levels.

One reson they fit those massive 1 farad caps in the boot.
Believe it or not I’ve seen the latter without any covers what-so-ever.

Problem most face is they deliver power via some you-beaut “oxygen free” cable with “gold” connectors and the return is via the rusted out chassis. Go figure. :o

i can forsee a lot of necessary existing onboard systems going “pop”.

PerryBebbington:
How much more voltage and why?

The alternator outputs the voltage it does because that is the correct voltage to charge the battery. Lead acid batteries have a tight window of voltage for charging them, go too high and they boil dry, too low and the don't charge. Not only that but the vehicle electrics are designed around the voltage the battery and alternator are set up for.

If you want a higher voltage for powering in car audio then either use a boost converter to get the higher voltage, or, if your skills are up to the job, install a second alternator and battery system from a lorry or other commercial vehicle with a 24V nominal output.

I need it to hold at 14.7-15.0V. The main issue is that the BCM wont even turn on the alt till the batteries are lower or the demand is high. The stereo doent trigger the load portion of that because the BCM has no idea whats going on turn the ac and headlights on and it will turn it on to 13.8 volts. At 12.8 volts my amp puts out 1528 watts. At 13.8 it does 1777. At 14.7 (when the battery were not match) 2175.

Because popping your ears is not enough... it also has to pop the windows?

Maybe you better put a spare generator on the trailer. That'd do the job.

I need it to hold at 14.7-15.0V. The main issue is that the BCM wont even turn on the alt till the batteries are lower or the demand is high. The stereo doent trigger the load portion of that because the BCM has no idea whats going on turn the ac and headlights on and it will turn it on to 13.8 volts. At 12.8 volts my amp puts out 1528 watts. At 13.8 it does 1777. At 14.7 (when the battery were not match) 2175.

14.7 to 15V will eventually damage your battery.

What is a BCM?

1528W at 12.8V implies a current of almost 120A. Add in any losses and it will be even higher. Forgive me, but I don't believe you, or to put it another way, if that's really true then I have indeed learnt something today!

2175W at 14.7V implies almost 150A. As I said above only more so!