Airgun silencer part 1
I’ve got a couple of airgun projects that have been in the back of my mind for years…
Ultimately I’m working towards an electronically controlled PCP.. but will start off with a CO2 .177
as a start, I need to know muzzle velocity… so designing a silencer that will measure the muzzle velocity is the first project.. whether this will be a standalone chrony type device, or have Bluetooth LE or maybe just a microUSB connector so it can be powered by a USB port (even an Android device).. but that does not have to be determined now…
So we start with a bit of a custom moderator… from Jaco @ airgunworx
the portion to the left that looks like a reel.. has 2 3mm holes going straight through… I’ll be using some 3mm infrared transmitter and receivers
I’m driving the LEDs from 5V through a 100E resistor.. I’ve tried the 330E too.. and the phototransistor has a pull-up of 1k to 5V. I need to play around with the values some more to get them optimized..
I’m using my .177 AA 410S TDR as test rifle, with H&N Sport Baracuda (10.65gr) pellets. The pellets are 6.6mm long and the narrowest diameter in the middle is 3.0mm.
Below you can see the test setup… and moderator and breadboard…
So looking at the initial results.. I notice that (with the phototransistor pulled up with a 1k or 1k2), I get 2 different wave forms based on the bias resistor of the LED the first (short pulse) is biased with 100R and the second (long pulse) with 330R. …although.. I’m suspecting there is something else at play here… further down where I show both pulses, they are biased by 110E abd they are around 30us long…
Below are the first results…
the sensors are 49mm apart and a time of 235us indicates a muzzle velocity of 684 fps
Next steps… optimising the biasing of the LEDs and the pull-ups of the phototransistors – currently the LEDs are biased with 110R (2x 220R in parallel) and 1k pull-ups on the phototransistors.
further I need to use a schmitt trigger – something like a 74HC14, to clean up the signal before passing it to the micro…
Just a quick sanity check… pellets are 6.6mm long… and sensors are 49mm apart… that would mean the pulse lengths should be around 7.5 times shorter than the distance between the pulses… thus approximately 30us…
…continued on part 2…