I have seen something similar for triggering the flash to take a high speed photo, but instead of using the breaking of the connection, it used two sheets of foil separated by a very narrow gap and when pierced they make contact, thus completing the circuit.
I've used this approach over thirty years ago, putting the foil on the outside of a 35mm slide frame, firing the strobe directly. (still have the same strobe!)
Of course, I can't prove the unit wasn't pre-triggered by the blast preceding the pellet
Alright I did some math. Since I tried to use infrared LED's (5mm) it turns out that at 400 FPS (feet per second) the bullet will only be in front of the LED for 39.583 microseconds. I saw in the above post that analogRead() takes about 100 microseconds. I actually tried my system and waved my hand between the 2 sets of LED's it did register with my program but returned nothing when the bullet passed by. What can I use that will work faster other than the foil method? I am looking for a lot of repeat uses.
Interesting approach to measuring projectile velocity.
I'm a minimalist at heart, always seeking the simplest way of doing things. This method does require good aim, though! ...and taught strips. If the foil strips sag, they tend to move aside rather than break.
arduinopi:
Alright I did some math. Since I tried to use infrared LED's (5mm) it turns out that at 400 FPS (feet per second) the bullet will only be in front of the LED for 39.583 microseconds. I saw in the above post that analogRead() takes about 100 microseconds. I actually tried my system and waved my hand between the 2 sets of LED's it did register with my program but returned nothing when the bullet passed by. What can I use that will work faster than the foil method? I am looking for a lot of repeat uses.
There isn't a practical speed limit to the foil method. It should have no problem with bullet speeds that the Arduino would be hard pressed to measure.
arduinopi:
Alright I did some math. Since I tried to use infrared LED's (5mm) it turns out that at 400 FPS (feet per second) the bullet will only be in front of the LED for 39.583 microseconds. I saw in the above post that analogRead() takes about 100 microseconds. I actually tried my system and waved my hand between the 2 sets of LED's it did register with my program but returned nothing when the bullet passed by. What can I use that will work faster than the foil method? I am looking for a lot of repeat uses.
There isn't a practical speed limit to the foil method. It should have no problem with bullet speeds that the Arduino would be hard pressed to measure.
sorry I forgot the word other (my power went out left out part of my post)
I was asking what is faster than the infrared LED and analogRead other than the foil method
I actually tried my system and waved my hand between the 2 sets of LED's it did register with my program but returned nothing when the bullet passed by.
Maybe this is a case of the bullet being too small rather than too fast. How are you making sure the bullet blocks all the light as it passes the detector?
Also, if you use the same read method for both detectors, what difference does it make how long the read takes? Won't the two read times just cancel out when you calculate the speed?
arduinopi:
sorry I forgot the word other (my power went out left out part of my post)
I was asking what is faster than the infrared LED and analogRead other than the foil method
Your best bet is to use something like the circuit I provided that produces a digital pulse when it detects an object breaking the beam, then connect that pulse to one of the digital pins and use an external interrupt to trigger your program logic. Use two devices (provided circuits). When the first is triggered, have your ISR record the start time (microseconds) and then when the second is triggered, have it record the stop time (microseconds) then you can process the speed using those times and the distance between the sensors...
