Next Launch Controller

[Fdog]

It's time to update my relay-driven controller. I'm trying to add continuity check at the handset as well as (currently only at) the pad control box.

The handset and pad controller are currently powered by a car battery at the pad, and connected by up to 500' of Cat5. I'm resorting to transistors to drive the continuity check, since it didn't make sense to use an out-and-back current flow to do that function.

Since I've never worked with transistors before, can someone with more skillz than me look this over?

...if the attachment doesn't work, the schematic can also be downloaded from here as a pdf. Or, the pages are as images here (page 1) and here (page 2).

Thanks!


All the best, James

[Fdog]

It's built. Amazingly it worked correctly from "first voltage". Testing it briefly, it worked perfectly with 500' of Cat5 as the wiring to the handset, and pops a 20A automotive fuse instantly.

The continuity check was measured as 2.1 mA at the microclips.

Part of my intention was to have the continuity circuit isolated when the arming relay was actuated.

...This isn't happening. It is possible to apply a faint trickle (~1.1 V) to the continuity circuit from the handset, when the arming relay is actuated. I've traced this to my choice of the 2N3904; I didn't realize that the orientation of the emitter would allow voltage passthrough.

I'll replace this transistor with a PNP, and change the handset switch to go to ground.

As with so many things, the fun has been learning about new things - in this case, transistors and stuff.


All the best, James

[qquake2k]

That turned out really cool looking!

[Zonie]

That looks nice. You can achieve the result you want by using a SPDT relay. Tie the POS clip to COM on the relay, and wire your continuity lamp to NC. Connect NO to the POS. You can put an arming relay on the POS to the PAD if you worry about fused contacts. The key switch goes in the low current control circuit that controls the coil on the relay(s). No need for Transistor switching circuits. (Although it is fun to design them)

I don't get the continuity check at the pad. I mean, when you test at the pad, you are potentially sourcing current to the igniter, while right next to the rocket.

As above, I use SPDT relays with the continuity check through the NC contacts. When I energize the relay for ignition, the continuity circuit is switched out and the NO contacts deliver full current to the igniter. If the relay is fused (as some folks worry about) and the igniter were to get full current when the key is inserted, then I'm safely away from the pad when if there is an errant ignition. With the test at the pad, you are not protected in any way.

You could add check at the pad by placing a pushbutton between POS and the NC contact but then you are next to the pad when testing...

My 2 cents...

[Fdog]

Good day Chris. My sincere thanks for your input, I'll take every helpful hint anyone can give me.

Your comments about using the normally closed contacts from the relay, are in fact, essentially what is done in this controller, so obviously we're on the same page.

Given the 26 Ohm resistance of 24 gauge wire over a 1000' loop, I was becoming concerned with implied load for a simple continuity check. Hence the transistors and their ability to amplify signal.

Yesterday I topped off the 12V battery to a no-load 13.2V. When measured across the clips, the continuity check was a mere 2.38 mA. After perusing this interesting article about igniter thresholds, I feel pretty good about the safety of pushing the continuity button at the pad.

Although I don't personally launch complex clusters, it was suggested to me to add the pad-side continuity check for these types of launches, so there it is.

Just for curiosity, I made up a 1000' Cat5e cable and tried it. The controlls operated cleanly and popped a 10A, 20A and 30A automotive fuse instantly. I was worried that I'd need to install relay drivers (more transistors) for that length of run, but apparently they're not needed.

I'll post the revised schematics tomorrow for those that are interested.


All the best, James

[Fdog]

Attached is the revised schematic. Also, this link points to the revised schematic as well.


The system as a whole. Not shown is 500' of Cat5 cable on a reel.



It certainly has been fun building this! I'll probabally continue tweaking the design because working with electronics has been very rewarding and a great learning experience. ...I sense a custom PCB in my future..


The Cat5 socket on the side of the pad control box. Wiring is conventional T568B, so any Cat5 cable will work.


As built, the internal load-carrying wiring is all 10 AWG. The clips are 14 AWG, and the battery connection is 8 AWG. All the miscelaneous low load wiring - the transistors, LEDs and buzzers & sirens, etc - are assembled on an experimenter's board.


Simple enough. Functions not seen: the Power LED will not light and an annoying piezo siren sounds if the system is connected with polarity reversed. Also, if the handset is ARMED, the siren sounds at the pad when the box is ENABLED.



The weak link on this is the IEC 60320 C14 connection to the clips - it is only rated at 15A continious. If I was to do this all over again it would be a NEMA L5-20.


The extension for the clips plugs in here. The extension is 8' of 14 AWG.



As with the pad-side box, all the low-power wiring in the handset are soldered to a experimenter's board. This became handy as I revised the Continuity circuit, and added protection diodes.


There's also a spare key safely tucked into the handset box...just in case...


I can't begin to express how much fun this was - learning about electronics, designing the system, learning through lots of trial and error. And, if anyone sees anything that I've done stupid, please let me know! Always looking to improve.


All the best, James

[Zonie]

I like the metal plate with the RJ45. Where did you buy that? A buddy of mine and I just built a pad using Cat5 and that connector would have been really nice.

[Fdog]

Well, ha-ha, oddly I had exactly the same problem. I tried to make a hole in the case that a standard keystone RJ45 jack would stay in...but no...didn't work. (if you look in the photos above, you can see where I had to patch the case with glass-filled epoxy)

I eventually found the part at L-Com, an online supplier. It's a metal panel mount that accecpts a keystone jack for standard punchdown.

Linky to the L-com page


The part # is ECF110C5E-BL at $5.95 each. I bought 4 since they were so inexpensive, I think I spent more in shipping than the cost of the parts. They're also available in black, yellow, white, etc.

It's actually a kit of the metal panel mount, and a keystone jack that you can punch down. I'm glad that's what I ordered, instead of a bag of 25 (for just the metal panel mounts) - I initially used a keystone jack from my own supply, a Hubbell, and it was a smidge too big. When I used the L-com jack it snapped right in.


All the best, James

[Zonie]

Thanks. We used a regular wall plate cut down. Made it easy to use a hole saw to drill a hole big enough to handle the connector and the plate was large enough to hide it.

[Green Jello]

Hey James....I just ran across this thread. That thing is really nice. Did you buy all the parts and switches online, or locally at places like Sandy Electronics?

[Fdog]

Thanks David!

I purchased everything from Sandy's, except:

The battery from Batteries Plus (behind the Olive Garden)
The jumper cables from Home Depot (they were on dirt cheap sale, $8)
The RJ45 sockets from L-Com (online)
Bolts & nuts to mount components inside from Lowes


For those that aren't from Reno, Sandy's is a local electronics component shop.

David, after using this for a year, one other thing I'd do is dispense with the Jumper cable clips, and use 75A Anderson connectors instead.


All the best, James

[Green Jello]

I had to research what 75A Anderson connectors were. Now that I know....are you saying that you install the receiving ends onto your igniters?

[Fdog]

No, instead of having jumper cable clips (the big copper ones) to connect to the battery, I would have a set of Anderson's permanantly connected to the battery. And, a set of Andersons on the red/black cable going to the pad control box.

That way you could easily plug the battery to the pad control box, and it wouldn't accidentally come disconnected.


All the best, James

[Green Jello]

OH, that makes much more sense. I read that too fast and thought you meant the alligator clips to connect to the igniter.

[cwbullet]

Very nice design. professional looking.

[Green Jello]

Hey James, I went by the new Sandy's today and things don't look good for them. I wouldn't be surprised if they aren't long for the world. Anyway....did you even get the boxes from them? Because I didn't see anything like that there.

[Fdog]

Well, that sucks. I knew they were moving, so maybe stock is still in transit? Hope that's the case.

The boxes I did indeed get from Sandy's. I would get the next size bigger for the Pad Control box, since it is a very tight fit inside.


All the best, James