16 Rocket Semi-Simultaneous Launch Controller

So about to buy parts for a Cub Scout model rocket launch control system! Yay!!!

It is made of multiple boxes, each with a big 12V battery and an Arduino, networked together. At the launch pads, each Pad Box needs to power both the static 5V control logic AND 12V through relays to between one and eight model rocket igniters. Although the RSO has the Master Arm, each Scout/LCO has their own Launch Button.

The big difference between systems I have seen elsewhere versus our needs: it seems almost all of the other multiple-pad controllers I’ve seen–one-person launches for all. But we want to continue to allow each Cub Scout (after the RSO arms) to control their own individual launch buttons. Most Scouts comply with the shared countdown & “drag race.” However there are often Scouts who want to “confirm their own control” or “call attention to themselves” by launching early or late! A little early or late, no problem…these “control freaks” may become real rocketeers someday! (But we do want the RSO’s master-arm to keep it within bounds).

So all of the individual launch buttons are merely gathered as inputs to the RSO’s Arduino control. Only when the Pad Boxes have their local power turned on do the Arduinos (or anything else) come on. Only when the RSO pushes the Master Arm do the Pad Boxes’ Arduinos get commanded to power on the relay boards. Similarly, only when the RSO’s countdown clock enables the two second window, then do the collection of launch button signals get forwarded to the Pad Boxes. So remove any of FIVE keys or momentary buttons, or the control logic, then NOTHING happens. Add in extra distance, buzzers, strobe lights, “Apollo-style” countdown/message display, Scouts launching from under a tent, “peanut gallery” watching/waiting under another tent… Well you see we take safety very_seriously indeed!

“Two heads are better than one…” So here it is, please give me your recommendations… Three Arduinos of some model(s), RS485 interfaces, driver/relay boards, all of it is open to suggestions. “Not too proud to beg.” Thanks in advance.

Seems part of this may have been answered in an “Archived” post. viewtopic.php?t=35116&sid=c3b043e584868 … ef67b7be82 But it seems they may not have brought over all of the recommended drawings… Suggestions?

Do SparkFun’s Arduino-compatible boards have opamps built in?

Bob-09816 and bob-14874 do.

Trying to learn KiCAD…still rough, but getting better. Finally enough drafted to share (and drown in the red ink as you all mark it up)… Thanks in advance for constructive criticism!

Showing just two of eight independent parallel igniter sub-circuits. And considering variations…DPDT vs. SPDT…Arduino source current for continuity measurements vs. dedicated constant current source…building driver/relay sub-circuits vs. buying an 8x driver/relay board…

Obviously just focused on the pre-launch continuity tests and one the launch signal handling. There ARE MULTIPLE power discos, removable keys, momentary “deadman” switches, and program logic safety measures as well!

Updated schematic… Thoughts?