24 Pad Launch Controller

This launch controller is set up for 2 banks of 12 pads each. A toggle switch (above the blue light) is used to choose the right or left selector switch. The controller uses standard grounded extension cords for control lines and displays the pad selection (red LED) and igniter continuity (green LED). The blue LED and piezo indicate arming. An auto ignition key was used as a removable arming key. The 2 selector switches are capable of handling 9 amps current or 1.5 amp make/break but are used only to select current into the coils of the 30/40 amp pad relays.

The main advantage to this design is that it uses durable and easily replaced extension cord and inexpensive 110v receptacles. This saves a LOT of money for the connectors. Only two features were dropped to allow this approach for lower cost and simplicity. The control has continuity detection at the panel but not at the pads and does not have a welded relay warning at the pad. (The photos were taken prior to the installation of the volt meter in the top center of the panel between banks of LEDs.)

The battery connector cable (white zip cord on left) is coiled and placed on top of the panel for storage.

CONSTRUCTION

The hardest part of the whole project was finding a suitable box for the controller. The one above was located at Tractor Supply. It has a plastic tray which was turned over to produce an excellent mounting panel for the switches and LEDs.

To maintain perfect alignment of the LED holes, a perforated board was marked and taped to the bottom of the panel. Holes were drilled, then the board was removed. Circuit boards were used to make the mounting of the LEDs more secure. The same perforated board was used to drill holes for LEDs, resistors, and connection lands for the wiring. The circuit board pattern was drawn on copper clad board with a sharpie and etched in ferric chloride. To my surprise, the Texas heat softened the hot glue used to mount the LED boards. So, at a launch, masking tape was used to retain the board until it could be better secured later.

For simplicity, the diagram below shows only one relay pad connected to the controller. It also does not show the second 2 wafer 12 position switch which would be connected to side side B of the DPDT toggle switch to support pads 13-24). If you only want 12 pads, then eliminate the A/B bank selection switch. If you only want one pad, then eliminate the 2 wafer 12 position switch and replace it with wire. The battery for the controller is separate from the pad batteries (which are located at each group of pads). You may wish to put a fuse on the supply to the controller.

Parts List:

1 PAD Qty	12 PAD Qty	24 PAD Qty	Description
1	1	1	controller box
1	5	8	ammo box (You can put 1 to 4 pad relays in each box for a given distance from the controller)
1	5	8	aluminum or steel sheet to make a panel face inside the ammo box
2	10	16	rubber grommets to protect battery cable where it enters the relay pad panel face
2	24	48	110v receptacles (note: Break both tabs off between wiring screws on each receptacle for 2 independent plugs per receptacle.)
1	3	4	12 ft automobile battery jumper cable (8 ga or 10 ga is all that is necessary) (K-Mart) (Cut them in half i.e. 3 12 ft cables make 6 6 ft cables.)
4	12	16	large ScotchLocks to connect the battery cables (2 per cable half)
1	12	24	12VDC (9.6VDC pull-in, 75ma) DPDT 15 amp plug-in relay - Radio Shack 275-218
1	12	24	10 amp relay socket - Radio Shack 275-220A
1	12	24	clear red T1 ultrabright LED
1	12	24	clear green T1 ultrabright LED
1	1	1	clear blue T1 ultrabright LED
3	25	49	plastic T1 led mounts
3	25	49	1k 1/2 watt resistors
1	1	1	fire button SPST normally open
1	1	1	keyed arming switch
1	1	1	toggle switch SPDT for selecting between banks)
1	1	1	momentary pushbutton switch SPST normally open - Radio Shack 275-609A (used for secondary safety pushbutton)
0	1	2	adjustable 12 position, 3 pole rotary switch (Allied Electronics C4D0312N-A)
0	1	2	1" knob for standard ¼" shafts - Radio Shack 274-416A (4 to a package)
1	1	1	12VDC (3.0-16VDC) piezo mini buzzer (7ma) - Radio Shack 273-074
1	12	24	6 ft ungrounded extension cords (for igniter leads)
1	12	24	110v pigtails (short grounded cords with grounded 110v plugs on them)
5	30	52	50 - Alligator clips (You'll need the extras for a multi-engine igniter whip)
2	2	2	battery clips (for launch controll battery)
1	1	1	8 ft length of zip cord
1	1	1	4 ft length of 1/8" heat shrink tubing
			Lots of - grounded extension cord for control wire (in 25, 50, and 100 ft lengths)
			misc.: superglue, DuPont spray adhesive, Exacto knife, wire, 12v batteries, launch rods, launch pads, deflectors

The launch control box does not pull much current. So, just use a couple of battery clips and some zip cord to supply the controller rather than the bulky jumper cable which the pad relays require.

Don't forget that you'll also need some 110v pigtails at the relay boxes to plug into the extension cords running back to the controller.

Don't let the loud annoying sound of this buzzer fool you. It is not overpowering outdoors and provides unmistakable indication of arming! You may wish to substitute a different buzzer for main control panel if you plan to announce the launches on a P.A. system but a finger on the hole during countdown in a better choice. (Extremely low current is not a requirement for the control panel buzzer and armed LED provided that the total current for the two is significantly below the pull-in threshold for the relay.)