Electronics > Projects, Designs, and Technical Stuff
My arduino powered firework sequencer. 2018 version!
usagi:
hi Stray Electron,
do you know offhand what typical resistor values are used for igniter safety shunts? commercial igniters are typically twisted shorted for transport, which would be effectively 0 ohms shunt :D I suspect commercial systems like cobra use some value like 10k.
texaspyro:
Some day I will write up my high power (fired many P class motors) model rocket launch system...
Radios are high power 915 MHz Xbees. Encryption starts with 160 bits of hashed password. Xbee channel and PAN codes provides 2^18 bits of unique radio id info. All messages are signed/verified with 32 bit cryptographically keyed message authentication codes.
The firing command is a challenge-response system using a 128 bit key / XTEA encryption and a 64 bit TRUE random number (generated from ADC and IMU noise, etc). When you send the ARM command to the pad, it responds with a double-encrypted version of a 64-bit true random number that the LCO box has to decrypt once and send back with the FIRE command. The pad controller decrypts that number the second time and the results must match the original number. The true random number generator has been verified against numerous random number test suites. The XTEA algorithm has been enhanced with extra rounds and a variable seed value.
Oh, and you have one chance and 20 seconds to crack the encryption between the ARM and FIRE commands... the crypto expires after that.
usagi:
--- Quote from: David Chamberlain on July 05, 2018, 07:37:35 am ---BTW usagi, I really enjoyed your video and detailed posts last year. Please let us know more about what you changed, or plan on changing, modifications and lessons learnt and so on.
--- End quote ---
For 2019 i've moved from mechanical relays to Darlington arrays, more integration onto single PCB. Lesson learned, put as much work into the PCB to avoid as much manual wiring as possible.
Also going to use pre-fabbed boxes probably from Hammond mfg. Constructing lasercut boxes is a lot of work.
Yansi:
--- Quote from: stj on July 04, 2018, 04:36:34 pm ---it's obvious most people here dont know electric matches are a virtual shortcircuit and need a MINIMUM 0f half an amp to fire - usually atleast double that to be sure it will go.
they arent like airbag triggers - they cant be fired by static.
--- End quote ---
Airbags can't be fired by ESD either. Even 9V battery is struggling to fire one.
texaspyro:
--- Quote from: Yansi on March 09, 2019, 02:38:03 pm ---
--- Quote from: stj on July 04, 2018, 04:36:34 pm ---it's obvious most people here dont know electric matches are a virtual shortcircuit and need a MINIMUM 0f half an amp to fire - usually atleast double that to be sure it will go.
they arent like airbag triggers - they cant be fired by static.
--- End quote ---
Airbags can't be fired by ESD either. Even 9V battery is struggling to fire one.
--- End quote ---
Electric matches have a "no fire" and "all fire" spec on current. Any current below "no fire" will not cause them to fire. Currents above "all fire" are "guaranteed" to fire the e-match. Some e-matches have surprisingly low "no fire" specs.
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