Yes

You will still be better off with a UBEC.  I use this one: http://hobbyking.com/hobbyking/store/__22494__Turnigy_3A_UBEC_with_Low_Voltage_Buzzer.html

It has a warning buzzer when your battery is getting low.

The 6.1V mode will plug direct into the barrel jack, or the 5.1V mode will plug direct into the 5v header on the Arduino for maximum efficiency.

It will run off up to 23V, so you can have lots of cells, high efficiency, and hence long battery life.

A preprocessor macro (#define) defined in a sketch cannot be referenced in a library.

It is a known (and often complained about) failing of the Arduino system.

Code:

digitalWrite (ledbar1[0], (a0c>i));

This does both the turning on and turning off...

a0c>i returns true or false.  True is 1, false is 0.  HIGH is 1, LOW is 0.

So it either turns the LED on (a0c > i) or it turns it off (a0c <= i).

So, if a0c is 2, the results are:

i=0, a0c > i, 2 > 0, TRUE, LED On
i=1, a0c > i, 2 > 1, TRUE, LED On
i=2, a0c > i, 2 > 2, FALSE, LED Off
i=3, a0c > i, 2 > 3, FALSE, LED Off

[1]

The trick is to look at things that repeat with only small changes.  In your code the following block is repeated with just a change of number:

if (a0c==1 || a0c>0)digitalWrite (ledbar1[0], HIGH);
else digitalWrite (ledbar1[0], LOW);

Replace those static numbers with a variable generated by a for loop, and you only have the block once.  eg:

Code:

for (unsigned char i = 0; i < 4; i++) {
  if (a0c>i)
    digitalWrite (ledbar1[i], HIGH);
  else
    digitalWrite (ledbar1[i], LOW);
}

Please clarify:

Do you want to:

a) Read data being sent by an Arduino using your PC, and save it to a text file on your hard drive, or
b) Read data being sent by some other device using an Arduino, and save it to a text file on an SD card?

The two things are radically different, so we need to know what you mean.

Did you read the wikipedia page I posted in my last reply about the envelope follower?

Right - it sounds like after demodulation you will have a serial signal.

However, "serial" is a very generic term.  Most of the time people say "serial" when they mean "rs-232", so connecting it to the RX input of the Arduino's serial port might work.

If it is rs-232 they should have provided you with baud rate and byte format (8-N-1 is most common - 8 bits, no parity, 1 stop bit, but it could be anything really).

The simplest demodulator is an envelope detector - this is basically what was used in early AM radios.  The output of the envelope detector may need some cleaning up before entering the Arduino to get it to the right levels - maybe a simple Schmitt Trigger buffer may be all that's needed.

(and seem a little too secretive)

That's often the case... Have you signed an NDA?

i was thinking to ask the company to provide me with a Tektronix Oscilloscope. I think they have the 2225 model (50 Mhz).  Would that help with this building process or is this not worth asking for?

A scope is one of the basic pieces of equipment all proper EEs should own.  I have a rather aged OS-9020A analogue scope (it was free).  I could do with a decent digital one to complement it too.  I prefer a proper analogue one for working with analogue signals, but you can't beat a digital one for working with digital signals - analysing protocols etc.

I use my scope daily - I think more than my DMM.

Also there is the underlying data encoding to worry about - is it a straight serial signal, or is it something like a manchester coding, or 8b10b, or what?  Without those kind of details it's not possible to do your job.

Is there an echo in here?

echo in here?

Ok.  So is the signal a lower-frequency digital signal encoded into a higher frequency analogue carrier wave?  Kind of like a radio signal?  If so you will need to de-modulate the signal, and for that you will need to know the modulation technique used - AM, FM, PSK, FSK, ASK, QPSK, etc...

Do you have a data sheet available for the device that is generating the signal?

serialEventRun() is called after every loop, but it then checks the availability of serial data and calls the serialEvent() function only if needed:

Code:

void serialEventRun(void)
{
#ifdef serialEvent_implemented
  if (Serial.available()) serialEvent();
#endif
#ifdef serialEvent1_implemented
  if (Serial1.available()) serialEvent1();
#endif
#ifdef serialEvent2_implemented
  if (Serial2.available()) serialEvent2();
#endif
#ifdef serialEvent3_implemented
  if (Serial3.available()) serialEvent3();
#endif
}

As the others have stated, what you ask makes no sense.

So, please furnish some more information, as what you are trying to do is either badly described (so we don't understand it), or you are going about it all the wrong way.

1. What is  this mystery 8MHz signal?
2. What do you want to actually do with it?

I'm asking for high level stuff here.  Not "I want to read it with the serial port", but "I want to do tell if it's pink, or if it's cheese flavoured".

http://www.cplusplus.com/reference/cstring/strtok/

In main.cpp in the arduino core:

Code:

int main(void)
{
    init();

#if defined(USBCON)
    USBDevice.attach();
#endif

    setup();

    for (;;) {
        loop();
        if (serialEventRun) serialEventRun();
    }

    return 0;
}

As you can see from that, any serial events are processed at the termination of each iteration of the loop() function.  It's not interrupt driven.

You can only reliably use the serial events if your loop() function doesn't run for too long (and certainly not if loop() never returns), so never ever use delay() unless you have modified your system to give the serial system a huuuuuge buffer.