Ladies and Gentlemen,
Model Rocket Launch Controllers certainly do seem to be a popular topic around here and I pray you will forgive me if I ask about yet another one.
I would like to create a Launch controller that uses an Arduino (and LCD screen) to display the results of a continuity check. (But I do NOT want to put the launch decision under control of the IC. I prefer to rely on mechanical switches for that).
To participate in the continuity check, I thought to put one of the pins of the Arduino into "input pull-up" mode (i.e. connected to +5v through a 20k-50k internal resistor and then activated when pulled low). That pin would attach to the high side of the igniter and pull it to ground when the igniter has continuity.
The problem I am trying to solve comes into play in the following scenario. A scout has pushed the launch button, and held it until the igniter has a chance to burn through (opening that connection like a fuse). Unless protected at that point, there is a conduction path connecting the Arduino I/O pin directly to the 12v supply. (see 10 ways to destroy an Arduino, Method #3)
My experience with electronics has been on a 20 year hiatus. Google and I have considered a number of solutions to this problem including several circuits designed for over voltage protection in power supplies (many found here in the forums). While terribly informative (and therefore entertaining), I think I have been off in the weeds.
The "10 ways to destroy an Arduino" link suggests a mechanism employing a Zener Diode (and a PTC fuse), but it was unclear to me how the Zener diode might affect the ground continuity test. (and the PTC fuses seem to be only available as surface mount components, I'm not sure about hand-soldering surface mount components)
I thought to solve the problem using a simple diode as shown in the attached PDF, Continuity.pdf.
What I would like to know is, is the diode shown in the diagram (I'm assuming something like a 1N4001) sufficient to keep the +12v supply from ruining the Arduino? Is the large current of the launch path a consideration? Will I need to take additional steps to isolate the Arduino from the +12V supply, and the large currents of the "launch path"?
For my current requirements in the launch path, I hope to be able to launch models that use both Aerotech (First Fire) and Estes igniters. According to links on the web like this one: Electrical Current Requirements of Model Rocket Igniters, I anticipate that the current in the launch path will be around 3A with a significant peak (12.39 amps for Estes igniters in the PDF).
Model Rocket Launch Controllers certainly do seem to be a popular topic around here and I pray you will forgive me if I ask about yet another one.
I would like to create a Launch controller that uses an Arduino (and LCD screen) to display the results of a continuity check. (But I do NOT want to put the launch decision under control of the IC. I prefer to rely on mechanical switches for that).
To participate in the continuity check, I thought to put one of the pins of the Arduino into "input pull-up" mode (i.e. connected to +5v through a 20k-50k internal resistor and then activated when pulled low). That pin would attach to the high side of the igniter and pull it to ground when the igniter has continuity.
The problem I am trying to solve comes into play in the following scenario. A scout has pushed the launch button, and held it until the igniter has a chance to burn through (opening that connection like a fuse). Unless protected at that point, there is a conduction path connecting the Arduino I/O pin directly to the 12v supply. (see 10 ways to destroy an Arduino, Method #3)
My experience with electronics has been on a 20 year hiatus. Google and I have considered a number of solutions to this problem including several circuits designed for over voltage protection in power supplies (many found here in the forums). While terribly informative (and therefore entertaining), I think I have been off in the weeds.
The "10 ways to destroy an Arduino" link suggests a mechanism employing a Zener Diode (and a PTC fuse), but it was unclear to me how the Zener diode might affect the ground continuity test. (and the PTC fuses seem to be only available as surface mount components, I'm not sure about hand-soldering surface mount components)
I thought to solve the problem using a simple diode as shown in the attached PDF, Continuity.pdf.
What I would like to know is, is the diode shown in the diagram (I'm assuming something like a 1N4001) sufficient to keep the +12v supply from ruining the Arduino? Is the large current of the launch path a consideration? Will I need to take additional steps to isolate the Arduino from the +12V supply, and the large currents of the "launch path"?
For my current requirements in the launch path, I hope to be able to launch models that use both Aerotech (First Fire) and Estes igniters. According to links on the web like this one: Electrical Current Requirements of Model Rocket Igniters, I anticipate that the current in the launch path will be around 3A with a significant peak (12.39 amps for Estes igniters in the PDF).
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