I recently tried to measure the initial speed of BB pellets. Currently, I am attempting to use a red laser and a TEMT6000 photodiode sensor to create a photogate detector. Since most BB guns have an initial speed between 100 and 165 m/s, I am using the digital pins of the Arduino, which have a higher refresh rate, for detection. The test results so far show that the detector responds to slower blockages, but it fails to detect BB pellets shot from the BB gun.
To investigate further, I used an oscilloscope to measure the output of the TEMT6000 and found that the output signal does not trigger the oscilloscope. I suspect that the response speed of the TEMT6000 is insufficient.
Therefore, I would like to ask for advice on the forum. For the application of "detecting the initial speed of BB pellets," are there any sensor solutions that are more suitable?
(I have currently found a photogate sensor: GP1A57HRJ00F, but I cannot confirm its effectiveness before purchasing and experimenting.)
The diameter of the BB pellet is 6mm. Assuming an initial speed of 165 m/s, the time to pass through the sensor is approximately 36 microseconds. (But since the BB pellet is round, the effective detection time interval should be even shorter.)
The TEMT6000 is a phototransistor, not a photodiode, and will be orders of magnitude slower than a good photodiode.
However, the inherent response time of the phototransistor is probably 1-2 orders of magnitude faster than "36 us", so the circuit and physical layout is most likely the problem.
Please post a complete schematic of the setup, including the light source and a photo of the layout.
That said, Vishay does not document the TEMT6000 response time, so you might look for a well characterized "fast" phototransistor, or consider a fast photodiode amplifier circuit.
It says: "Rise and fall times depend (drastically) on the load resistor that is used. For all these ALS phototransistors these are in the range of 45 μs with a 50 Ω load resistor and rises linearly to 310 μs with a 10 kΩ load resistor.
To achieve faster rise and fall times, it is also important that the collector current is as high as possible."
But I not sure it is the reason that can't work for BB bullet detection.
The major concern is the response time of the sensor.
Jremington said: "The TEMT6000 is a phototransistor, not a photodiode".
As I found the document:
it says: all these ALS phototransistors these are in the range of 45 μs with a 50 Ω load resistor and rises linearly to 310 μs with a 10 kΩ load resistor.
So, I think the better way is change the sensor from phototransistor to photodiode.
And the red laser that I used was not pulse modulated.
