Making a Parallax Propeller chip based chronograph

[Solar]

So I have read other threads regarding inaccuracies in readings with chronographs using Arduino boards but what about using the multi core Propeller? With 8 cores the effective clock rate ranges from 32 kHz up to 80 MHz which should be plenty fast to read the input from infrared sensors and avoid the use of interrupts. Using a stable 5mhz external crystal to maintain consistent clock speed would also be useful. Other cogs are reading data from the laser range finder and operating the launch controller in the latest pneumatic launcher I am building. By using one cog to read the data and another to calculate and a third to display everything there should still be three cogs open for other things. Has anyone tried using the propeller for such a project before?

[Technician1002]

If the board can indeed capture at that rate, it should be reasonably accurate if you can get the optics to work. Sometimes the interface between an analog sensor and reliable machine detection can be difficult. Are you good with analog? Everything from condensation on air cannons, to flame fronts and particle ejection can cause false sensor events. It is one of the reasons I went magnetic instead of optical. I used a 100 Mhz scope for measurements. An audio recorder able to capture at CD quality (44.1K) also works very well.

[Solar]

I am planning on placing the sensors at the beginning and end of the six inches of porting on the barrel as a launcher mounted chronograph. We use case-less rounds with no wadding but perhaps a thick enough cloud of condensation could block the infrared sensors as you say. I am just getting back into programming and electroincs as I have been away from both pursuits for some years. The propeller chip is a great little chip and we already have one on the launcher so ot makes sense to utilize it. What type of 100 mhz scope are you using? I am not familiar with magnetic sensors other than hall effect sensors, but would a non metallic onject still afffect the sensor?

[Technician1002]

I do electronics repair so the scope is an older Tektronics bench scope with digital storage, so I can trigger a single event and save it. My pickup is a simple magnet and wire coil arrangement, so it does not work with non-magnetic projectiles. For a shirt launcher, a small magent is rolled into a shirt and launched. Working with the analog trace, marking the point where the magnet is neither entering or leaving the coil (center crossing) results in a 0 volt centerline crossing for precise projectile posiiton sensing on launch.

Barrel based optical sensors can work if you do not have issues with flame fronts, particles, condensation, etc. Biasing IR to work outdoors in sunlight can be tricky as the field is heavily blanketed in IR noise. Many items that are black in visiable are transparant to near IR. Tinted windows and sunglasses are a couple of examples of IR transparant materials. Viewing IR photography sites reveal supprising things like in IR a glass of Coke is water clear.

[jimmy101]

If you use both IR illumination and IR sensitive detectors built into the barrel, or ported part of the barrel, you should be able to handle background light pretty well. Plus things like steam are pretty transparent to IR (heck the human body is pretty transparent to IR).

As far as speed of the timing system is concerned you just need to ask the basic questions;
1. How far apart are the detectors?
2. What is the maximum velocity I expect?
3. How <strike>accurate</strike> precise do you want the chronometer readings to be?