Pyro Channel For Custom Flight Computer Inquiry

Astromaster

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Hi, I am a beginner with some experience related to electronics and have started designing a custom flight computer with the intention of trying to learn more about rocketry and avionics. There are 4 pyro channels in my computer and one of the features I would like to have is some form of 'continuity detection' on all 4 pyro channels. What I mean by "continuity detection" at least by the standards I have set for this project is nothing fancy. I would just like to be able to detect if my charges(whether it be firework igniters or other forms of black powder charges) are properly connected/hooked up to the pyro channels/terminal blocks without the use of LEDs. This feature is not imperative for the overall functionality of the flight computer however I have set it as a must-have in my design because I think it would just be a cool challenge and be a nice feature to have; however, I have not the faintest idea on how I may implement such as feature with the schematic I currently have. I have searched across the internet looking for something that may help but to no avail. The closest resource I have found is the image posted below on a basic continuity detection system; however, I fail to see how I can implement that design safely with the voltages that I am using.
1623887239056.png
Below is a screenshot of the schematic for my pyro channels without any continuity detection. I am using an N-Channel 12V(D-S) MOSFET with a Vds of 12V and a VGS of +-5. The gate is connected to a pin on a MK20DX256VLH7, commonly known for being the central processor on the teensy 3.2. Additionally, the 12V battery I have spec will run between 300-450 milliamps of current. I am new to this forum so please let me know if there is any further information you might need on the computer, and I want to thank anyone ahead of time for helping me with this project.pyrochannels.PNG
(P.S the igniter with be connected to the two pin terminal block shown in the image)
 

jderimig

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For continuity put a 10K total resistor voltage divider from drain to source. If you have continuity ~1ma will run through the igniter. You tap off the voltage divider to a digital input pin to sense. If not continuity this voltage will be zero.

To fire commercial ematches your battery needs to supply more than 300-400ma.
 

Astromaster

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Interesting, however, would the power dissipation from the resistor be an issue considered we are converting 400mA to 1.2mA?
 

rocket_troy

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Interesting, however, would the power dissipation from the resistor be an issue considered we are converting 400mA to 1.2mA?
Not sure what you're getting at there, but 1.2mA is not much current. Because it's a divider, the resistance is actually 20K between your pyro and source - the impedance of the digital input will likely be much too high to worry about, so that's already 0.6mA through each resistor. Power: because it's a divider (assuming equal value resistors) you can halve the rail voltage to assume the voltage drop across each resistor so, P = VI = 6Vx0.0006A = 3.6mW dissipation through each resistor. That's not much power, but if it was too much for you, then simply increase the ohmic value of your resistors.

TP
 
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