Sorry I got confused with single-coil dual-winding/two cylinder bike engines, they fire on exhaust stroke. The Royal Enfield is a 4-stroke some models with dual-sparkplug, so I figure 2 revs/spark.

2000RPM/60=33.3Hz crankshaft speed/2 = 16.67Hz ignition frequency.
At 800RPM =6.67 Hz, at 8,000 RPM = 133.3Hz
At 800RPM =150msec, at 8,000 RPM = 15msec between pulses

I would use a timer on the Arduino to measure time between ignition pulses and convert to RPM.
You are using the LM2917 to drive an analog meter? See page 10 on app. note http://www.national.com/an/AN/AN-162.pdf
also thread here: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1237171773


A capacitive ignition sensor can be made with a couple turns of wire wrapped around the spark-plug wire and then into the 555 circuit. I have never found a source for inductive pickups. You can make one with a split ferrite core (like EMI snap-on cores).

You have to pulse an IR led to transmit data. Sparkfun website is down so not sure what you got. People use a 555-timer chip circuit http://jap.hu/electronic/infrared.html to generate these fast pulses, which the micro then turns on/off to send data. Samsung standard is 39.2kHz and RC-5 modulation (32 bit, 1 start, 1 stop) is popular), more info here:
http://www.techdesign.be/projects/011/011_waves.htm

I think you have two things to sense.
When the lenses are at (either) end of travel, you need 3 or 6 (home) limit-switches also. VCR's use a small hole drilled in the gear with opto-sensor, or microswitches and a cam lobe to find home.

Next, to measure position- a slotted (quadrature) optical encoder wheel, from an old computer mouse, old DSLR lens or plastic cutout from laser print out. A hall-sensor on the motor might work but I have not tried. The gear teeth themselves are really small and aligning the sensor would be difficult.

What I have done is used ~1" plastic tubing to connect a rotary encoder to the mech. shaft. The tubing allows misalignment and stretches snug on the shafts, or use glue/clamps but it's low torque.

I couldn't find a datasheet, but I did cross-reference it to NTE3100 with pinout here: http://www.nteinc.com/specs/3100to3199/pdf/nte3100.pdf
Or you can use a multimeter on diode-test to ID the LED pins and the phototransistor if you shine a light on it, it will turn on.

   if your bike is a 4-stroke engine, you get a spark every 4 engine revolutions. If your bike is a 2-stroke engine, you get a spark every 2 engine revolutions.
2000RPM/60=33.3Hz crankshaft speed = 8.33Hz (4 stroke)  or 16.67Hz (2 stroke) ignition frequency.

Wait - do you have the pinout correct on the BC546 C-B-E? It looks like your excess current is not the LED's staying on, but the Arduino outputs staying high during sleep mode and driving the transistors? First you need a base drive resistor a few kohms, never direct. Second you can drive the pins low, or pinMode them to inputs before you go to sleep, to save power.

I've been assigning SPI pins CS,MISO,SCK,MOSI as input/output pins with pinMode(), and enabling pullup resistors on CS and MISO in Setup(). With a scope, I noticed these pins can float and cause weirdness. Check it by touching them with your finger and seeing if things change.
I'm not sure what the MAX6675 library does for SPI setup, but it's good for 4.3MHz SPI which seems fast enough.

The LTC2418 24-bit A/D is a real bear to get working ] The conversion data and channel numbering are from Mars. Its output data is "somewhat" 2's complement- there are status bits to tell -ve or +ve over range and I finally have a signed long for the conversion (I will post my sketch in another thread once I get it finished). I need a float to print voltage.

Code:

//This code works fine, I get a float with the static(?) cast:

signed long adc_value;

   adc_value=getAtoD();
   adc_result= (float) adc_value;
   adc_result= /838860.8; // R divider 9V max; A/D=2.5Vfsd
   Serial.println(adc_result,4);

However, I went to using a union to store the A/D data and it doesn't work properly:

Code:

union
{
  float v_modem;    // Ch. 4 scaled voltage 0-5V
  float v_solar;    // Ch. 3 scaled voltage 0-5V
  float modem_vreg; // Ch. 2 scaled voltage modem vreg 0-9V
  float I_monitor;  // Ch. 1 scaled current 0-2A
  float v_board;    // Ch. 0 scaled voltage 0-9V
}
adc;
//--------------------------------------

void mysub() {

signed long adc_value;

  adc.v_board = 0.0;
  adc.I_monitor = 0.0;
  adc.modem_vreg = 0.0;
  adc.v_solar = 0.0;
  adc.v_modem = 0.0;

  adc_value=getAtoD();
  adc.v_board = (float)adc_value/838860.8;

  Serial.println(adc.v_board,4);
  Serial.println(adc.I_monitor,4);
  Serial.println(adc.modem_vreg,4);
  Serial.println(adc.V_solar,4);
  Serial.println(adc.V_modem,4);
}

V_board is correct i.e. 6.0512V but ALL channels in the union have the same value 6.0512V 

I found my USB hub made things not work properly- connect directly to your PC.
Then uninstalling the USB driver then reinstalling in Windows7 fixed things.
I go to Computer->Manage->Device Manager and see if connecting/disconnecting the Arduino shows COM port assignment.
COM1 can be your motherboard RS-232, not a USB assignment.

I had some hassles with the Mega2560 under Windows7. It does not use the FTDI USB chip, instead uses Atmel 8U2 so I had to load the USB driver from drivers\Arduino MEGA 2560.inf ...  but not so with the Mega328.

I have a 24-bit signed quantity (from A/D converter LTC2418) and need to convert it to a float (voltage). I'm finding this really hard and not sure where things go wrong. I get the 24-bit A/D data and sign-extend into a 32-bit long:

signed long adc_value;

   adc_value=getAtoD();
   Serial.println(adc_value,HEX);

   adc_result= (float)adc_value;
   Serial.println(adc_result,2);


Results
A/D data:
0xC0000000 (+2.5V fullscale) sign extends to -> 0xFFC00000 gives-> -4194304.00 (expect 838608.00)
0x80000000 (zero)               sign extends to -> 0xFF800000 gives-> -8388608.00 (expect 0)
0x7FFFFFFF (-1 LSB)            sign extends to -> 0x007FFFFF gives->  8388608.00 (expect -1.00)
0x40000000 (-2.5V fullscale)  sign extends to -> 0x00400000 gives->  4194304.00 (expect -838607.00)

I can't understand why the values are off.

How do I disable the Mega2560 from powering up via USB? I am supplying external power VIN and only want to use that, as the current drain is too high for USB. The voltages are too low when USB is connected.

byte d[4];
long adc_value;

<.... stuff deleted>

adc_value  =  (long)d[0] << 24;
adc_value += (long)d[1] << 16;
adc_value += (long)d[2] << 8;
adc_value += (long)d[3];

This code works fine now. (Without proper casting to a long, I get swapped nibbles i.e. 21346587)
Thanks to everyone, esp. jraskell for the help.

Yes it should be: unsigned long adc_value; but I get the same results.

It is the missing brackets on SPI.begin() that cause it to hang at run time.
Thanks everyone for your help.

I do get interesting results and am still looking for a solution. It looks like the shift operator is only 16 bit. The cast to a long swaps nibbles on some of the bytes, which is strange. Thanks everyone for your help so far.

  byte d[4];
  long adc_value;

  d[0]=0x87; 
  d[1]=0x65; 
  d[2]=0x43; 
  d[3]=0x21; 

  adc_value=0;
  adc_value += d[0] << 24;
  adc_value += d[1] << 16;
  adc_value += d[2] << 8;
  adc_value += d[3];
  Serial.println(adc_value,HEX); //--> prints 4321 (expected 87654321)

  adc_value = *((long *)d);
  Serial.println(adc_value,HEX); // --> prints 21346587 (expected 21436587)

  d[0]=0x12; 
  d[1]=0x34; 
  d[2]=0x56; 
  d[3]=0x78; 

  adc_value=0;
  adc_value += d[0] << 24;
  adc_value += d[1] << 16;
  adc_value += d[2] << 8;
  adc_value += d[3];
  Serial.println(adc_value,HEX); //--> prints 5678 (expected 12345678)

  adc_value = *((long *)d);
  Serial.println(adc_value,HEX); // --> prints 78563412 (expected 87654321)