high speed camera and some sort of measuring device as a back drop.  Then calculate.  There may even be a cell app that does that or you could change recording speed of your camera.

High speed cameras are some of the things I don't have.  And it sounds rather complicated to figure out how to set up the cameras and make them work.  The reference board (for want of a better term) would have to be rather substantially built to withstand the muzzle blast and it would be a one time use item.

I'm really looking for a simple electronic alternative to the LEDs in the design referenced.

I have experience with high speed cameras. They're not cheap, but they're actually quite easy to use. You install software on your PC, connect the camera with an Ethernet cord, and record some footage. The difficulty comes in achieving high enough frame rates without dimming the image too much. The higher the frame rate, the more light is necessary to produce a bright enough image. The cameras are also relatively expensive.

Unfortunately with the smoke and debris, you're not going to be able to use optics to achieve your goal. Even IR won't cut it with the heat from the blats. You'll probably need ultrasonic or RF.

I realize IR or some other optical thing won't work.  That's why I want to use a conductive wire where other's have used IR.

This has to be low cost so high speed cameras are out.

You can likely achieve this with an Arduino accurately enough. You can set two pins as outputs and two as inputs. Connect two wires between inputs and outputs to create your trip wires. You'll need at least 100 ohm resistors I'm series with the wire to limit current draw. Then in the program, you would initiate the pins, turn the output pins on, then continuously poll the input pins and record a timestamp when the input goes low. The Arduino should have a fast enough clock that your speed will be pretty accurate, especially if the polling is the only thing you do.

Unless the projectile is VERY slow and the measuring distance very large few computers can sample an input fast enough.

You won't be able to have you wire as close as a ballistic chronograph, but it is very doable, even with a "slow" Arduino.

An Arduino processor operates at 16MHz. If you placed the first wire 10 feet from the muzzle (to prevent the air from inside the barrel in front of the cannonball from affecting it), and the second wire at 20 feet from the muzzle, the Arduino should definitely be able to measure it.

I appreciate the suggestions but I am pretty sure the recording device (computer sound card) will work for me.  I have a sacrificial laptop that I will use so I don't fry my good computer.  

What I need is something to replace the LEDs that will not be effected by the flame and smoke.  Here is an example of my cannon and the muzzle blast from a 3 ounce blank cartridge.  I will be experimenting with the, then standard, charges of 4, 5, 6, and 8 ounce cartridges to determine range, velocities at various ranges, and energy.  The cartridges use cannon grade powder.




I also think that if I replace the LEDs with a wire and a "something" to provide the correct input voltage and amperage that mimics the operation of the LEDs I will have what I need.


I read somewhere that when the British developed this gun they found it had a range of approximately 1700 yards at 3 degrees of elevation.  if that is correct, using the formula found on Ulrich Brestcher's webpage (http://www.musketeer.ch/blackpowder/proving_mortar.html) I found that the velocity should be about 1,275 ft/sec; the free software (coilchrono) available on the web at archerytalk.com should handle this.

Processor speed is very much faster than software execution speed.
You are in a fantasy.

Even if it has a hardware timer you are going to need hardware access to fast signal pins to start and stop the timer.

Any LEDs are used to illuminate a photo diode or photo transistor.
LEDs do not sense anything.

See?  I do need help, I don't even know the correct terminology!

When Oehler was the only game in town with optical sensor the units cost over $1,000 each.

I designed and built a compete ballistic chronograph.
Z80 processor to execute the math and a hardware timer chain to count a 10 MHz clock.

EEPROM memory came in 32 kbyte chips.
SRAM was 1k x 4 chips.
DRAM existed but was only 32k x 1 and needed a lot of hardware to maintain refresh.
The Z80 had limited DRAM support built in.

Photo-diodes to catch the shadow of the bullet across the sensor.
Making the half cylinder slightly curved lenses to focus the light onto the photo-diode was a nightmare and a half.

If you need a small number of measurements, you could hook two cardboard discs up to a rotating axle.  If you know how fast the axle is rotating (rpm) and the distance between the cardboard discs, you can calculate the time between the two discs based on the difference in angle where the holes are and hence the velocity.

Look it up on google.

Wait till you try and use a camera of any type to record the image.

You could make two loops of wires that acts as antennas of pickups, and generate a change in voltage/ frequency when a metal object passes through them.  Next step is being able to capture the two changes in voltage, then figure out time and distance from how they are placed.  Maybe the first field activates the timer, then the second field stops it?

I helped out someone two years ago bury a loop of wire encased in PVC pipe under their driveway, and that acted as a trigger when a large metal object crossed over it.  The detection circuitry was in the gate controller.

Build the chronograph you have plans for and place it fifteen feet in front of the muzzle.  That's what's done with standard chronographs to prevent them from reading the muzzle blast.

No, I mean you shoot a hole through the two discs and measure the angle difference between the holes.

The wire would work fine. It can be tin foil too, anything conductive. You would be splicing a circuit onto a headphone jack and using the sound card to record the data. The old chronos did this, before optical ones.

Not sure of the circuit, it would likely be "parallel" loops, each having a different high resistance. In use, the signal would be level until the shot broke the first loop, which would cause a large change, and then a large change when the second loop was broken.Use 'Audacity' to measure the time differential between the spikes, then do the math.

And you measure the RPM how?

Sound cards sample how fast?
And with what bandwidth?

Not interpolated reproduction numbers.
Hard samples.