Does This Schematic Look Correct For Launch Controller?

[cj cake]

I am less than satisfied with my current launch controller and decided to buy/build a replacement. After searching the internet, I did not find a controller that did everything I want it to do. I found a lot of DIY controllers and was inspired to try to build my own. I stole a most of these ideas and circuits from other people and modified everything to meet my own wish list for a control system.

1. Launch up to four rockets either one at a time, or all at the same time, or any combination.
2. Allow multiple engines (clusters) to be started at once in the same rocket.
3. Use a relay with the battery at the launchpad.
4. Use an inexpensive cable for distances of 100 feet for safety.
5. Lots of lights and buzzers for the fun factor.
6. Keyed master power switch.
7. Batter voltage indicator.

What I was going for was something like this:
1. When the keyed master switch is turned, the voltmeter comes on and a "System Armed" LED lights up.
2. If any one of the four circuits is connected to an ignitor or the "Fault Test Light", A continuity LED comes on for each pad connected.
3. The Pad select switches will be guarded toggle switches. When one is lifted to arm a pad, the "Pad Select" LED will light and a piezo buzzed will sound.
4. Finally after an audible countdown, the launch button is pressed to light off any selected pad ignitors.

I attached my two schematics and a couple images that show my inspiration for this project. I like the look and layout of the yellow box, but I want to four pad capability of the relay box in the pictures.

Does the schematic pictured seem correct? Is there any issues with the wiring plan? Any better way to do this? I will take all the criticism you can throw my way.

Thanks,
CJ

 

[UhClem]

The continuity LEDs are useless as they only show that a relay coil is connected. Which it always is.

One arm warning buzzer is sufficient.

A pad side safe/arm switch would be a very good idea. As would be a continuity test.

DARS equipment.

 

[Jeff Lassahn]

What's the thinking behind making the current return from the buzzers go through the data connection to the relays instead of directly to ground?

 

[cj cake]

Good catch I didn't even think about the continuity only checking that the coil was connected. I will move the continuity circuits over to the relay box near the pad and I will install a safety switch as well. Thanks for catching that mistake.

 

[cj cake]

What's the thinking behind making the current return from the buzzers go through the data connection to the relays instead of directly to ground?

Reply removed, let me read your question again and think about it. II misunderstood the first time.

 

[cj cake]

What's the thinking behind making the current return from the buzzers go through the data connection to the relays instead of directly to ground?

Good point I just looked at it again and I have no idea why I did that. It would just need to be in parallel with the LED from the pad is selected and armed.

 

[g.pitts]

It's pretty common in electrical design to see either a diode (or Zener diode) across relay coils (cathode of diode goes to the +V side of the relay). Inductive kick from breaking the voltage applied to the relay coils upon switch release will generate very high voltages, which may erode your switch in relatively short order.

<edit> The diode needs to be capable of handling a decent amount of current. Avoid "high speed switching" diodes and lean toward power diodes. I found a write-up on the particulars behind the principle here.

 

[Kelly]

+1 on what David, Jeff, and Gene said, ESPECIALLY the arming switch at the relay box. In addition, your controller box schematic seems incorrect for pad #4, the buzzer output goes to data connection #3.

 

[cj cake]

I tried to make all the suggested changes and fix some of the foolishness I designed into the first version. Is this any better?

 

[g.pitts]

I tried to make all the suggested changes and fix some of the foolishness I designed into the first version. Is this any better?

You need to reverse the direction of the suppression diodes on the relay coils. Currently, the cathode is tied to ground which will cause bad things to happen.

 

[cj cake]

I didn't catch that one. Thanks! It is fixed now.

 

[cj cake]

I made an additional change to the launch control box. I hope this didn't screw everything up.

If I am only going to launch a low power rocket from one pad, I want to use the same launch controller box, but eliminate the need for the relay box and battery. So I added a "Pad 0" or "Relay Box" selector switch. If It is switched to Relay box, it will operate as it does in the last version. But if you select Pad 0, the other circuit becomes active and you can then plug your wires directly into this box and launch.

 

[g.pitts]

I made an additional change to the launch control box. I hope this didn't screw everything up.

If I am only going to launch a low power rocket from one pad, I want to use the same launch controller box, but eliminate the need for the relay box and battery. So I added a "Pad 0" or "Relay Box" selector switch. If It is switched to Relay box, it will operate as it does in the last version. But if you select Pad 0, the other circuit becomes active and you can then plug your wires directly into this box and launch.

One observation is that your voltmeter is in series with the resistor and power LED. You probably want to put the voltmeter in parallel with the resistor and power LED. Otherwise you'll read a lower voltage than actual. I didn't go any further, but will today if I get time.

<edit> Looking at the schematic once more, I see that the "Armed Buzzer" is in series with your arming LEDs. Will you get enough current flow through the buzzer to feed your LED path(s)? If you happen to be planning to use a piezoelectric buzzers (a lot of dB for the power consumed), they don't draw much current at all and may starve your LED(s).

 

[UhClem]

<edit> The diode needs to be capable of handling a decent amount of current. Avoid "high speed switching" diodes and lean toward power diodes. I found a write-up on the particulars behind the principle here.

It doesn't need to handle any more than the steady state coil current and that is in the form of a pulse. So a 1N4148 switching diode is adequate for most automotive 12V relays.

This relay has an 88 Ohm coil so with 12V applied (it will be less thanks to wire resistance) the current will be 136mA. Which is within even the continuous duty limits of the 1N4148 so a pulse is no problem at all.

 

[cj cake]

Thank you for all the help. I ordered most of the components today and I hope to start putting it together soon. I will post updates as I find time.