INTRODUCTION
The system described here is a major revision of my launch controller
and pad box designs used by MARS
Section 136 of the National
Association of Rocketry (NAR). The earlier design is documented in my
NARAM 39 R&D report: "32-Pad Launch Control System".
The system employs several innovative features designed to solve
common launch system limitations:
UPDATED features:
- A new modular design
separates the main console into three smaller circuit boards:
master/encoder board (one is needed), 16-pad driver board, and a 16-pad
continuity/display board. This makes it easier for an individual to
etch their own set of smaller boards (the previous version was a large
8x10" board for 32 pads).
- By adding slave console boxes
"daisy chained" from the master console box, up to 256 pads may
be used.
- Console boards may be stacked
side-by-side within a larger main console, or stacked vertically within
individual slave boxes.
- The main encoder circuit is a
more reliable design based on a small PIC microcontroller (eliminated 4
larger IC's).
- The pad box circuit also has
a small PIC microcontroller to allow easier mode detection and unique tone
generation. There are tones for continuity (variable pitch for
igniter quality), armed mode (pulsing tone), low-battery mode (two-tone
pulsing), and relay fault (siren sound).
Previous features:
- The main control
console uses a digital rotary encoder to select the pad. This eliminates
the accidental launching of multiple rockets with the typical array of
toggle switches, and it solves the problem of finding a 32-position
mechanical switch. A reliable digital control circuit replaces the
mechanical switches for long-life operation.
- The main control
console gives visual continuity indication (and 'armed' indication) for
all pads simultaneously. There is no need to select the pad to check the
igniter. This feature allows for faster operation on a busy rocket range.
- Each pad control box
incorporates a low-cost, high-current relay with the option of adding a
local pad battery at any launch pad (for clustering, or distant pads). All
pad boxes are interchangeable — for model rocket pads, high-impulse pads,
or "away cells" — allowing the widest variety of range layouts
using the same equipment.
- Each pad control box
has a novel continuity circuit which produces a variable pitch tone to
indicate igniter quality. A good (low-resistance) igniter gives a
higher-frequency tone, and poor (higher resistance) igniter gives a
lower-frequency tone. Problems such as weak igniters or dirty clips are
audible both at the pad and at the main controller. This test
circuit is safe for all types of igniters.
- The pad boxes have
several safety features: 3-way toggle switch for TEST-OFF-ARMED modes; a
pulsing tone when in the ARMED position; and a warning tone for
"stuck relay" when in the TEST position. The pad boxes are
protected by a low-cost thermal circuit breaker to prevent long-term short
circuits from draining the battery or damaging components.
- The cost of cabling is
greatly reduced by using the same single pair of wires for both the launch
signal to a pad and the continuity signal from a pad. A third wire is used
only when supplying power from a centrally-located battery. For
combined power and signal distribution, low-cost standard outdoor power
cords are used.
Please note: The information published here is free to
individuals and clubs for non-commercial use. All rights are reserved for
all other uses, including commercial products, and publication of all or part
of the design without written permission from the author. Some features
are patent-pending. The author will not be held liable for any damages or
losses incurred through the use of the information on this wesbite.
Updated 8/10/2002, John DeMar.
(c)2002