Missile Works PET2+ Manual

User Manual and Instructions
PET2+ Programmable Event Timer
Version 2.0
System Overview
The PET2+ provides a highly advanced and versatile dual-event timing control system targeted for
high power rocketry. The design of the PET2+ utilizes a RISC microcontroller with a precise internal
factory-calibrated 4MHz system clock for accurate and reliable event timing control. In addition the
PET2+ uses a 3-axis “micromachined” accelerometer to detect specific inertial events during flight.
Some of the applications that can be achieved with the PET2+ timer include:
·Precise booster separation and sustainer ignition of multi-stage composite powered rockets
·Ignition of secondary composite motors after primary motor ignition for airstarted boosts
·Fail safe backup and redundancy of primary rocket recovery control systems
·Triggering a camera shutter, audible/visual tracking device, or other electrical devices
General Specifications
Arming Mode Inertial/Breakwire Battery/Power range 6-10 VDC
Dimensions 1" W x 3.15" L Continuity current 9μa @ 9V
Inertial G trigger range 2-5 G’s Nominal Battery load 6-14ma
Output current (sinking) 3A @ 0.5 sec Weight 17 grams
Handling Precautions
·Always handle in a properly grounded environment. ESD damage is not warranted.
·Never touch/handle the unit when it is armed and connected to live pyrotechnic charges.
·Allow the unit to adjust to ambient temps prior to arming/flying, and avoid extreme temps.
·Never arm the timer and then load your rocket onto the launch rail. Arm ONLY when racked.
·Always prepare your rocket and timer system components with the unit powered off.
All user input and output connections are made to the compression terminals as shown. These
terminals include: Battery (logic and/or pyro power), Breakwire (for a N/C wire loop or switch), and
Event1/Event2 (for external pyro events or controls). All terminals are marked on the board silkscreen
for reference.
Page 1
Note: Before using the PET2+, familiarize yourself with the location and designation of all the
user connection terminals, pushbutton controls, and with the audible feedback and LED
functions. These functions, operations, and connections are covered in subsequent sections
of this manual.
Pre-Flight / In-Flight / Post-Flight Modes of Operation
The PET2+ has several distinct modes throughout the course of its operation during flight. These
modes of operation are easily identified by the function of the piezo and the LED.
Power-up mode
When power is first applied to the unit, it will provide a continuous 2-second chirp to indicate it has
been switched on. During this 2-second chirp the LED will be solid RED.
Accelerometer initialization mode
After the Power-up mode, the unit goes through a 10-second accelerometer initialization start-up
delay. The LED will flash slowly in YELLOW while in this mode. This delay period allows stabilization
of the device and establishes the initial orientation and inertial references.
POST (Power Up Self Test) Verification / Error Chirp Mode
The PET2+ performs several sanity checks after initialization mode based on its current configuration
to ensure that the rocket and timer are oriented properly and within allowable launch angle and
calibration limits. If using the Breakwire trigger, this input is also checked for a proper “closed loop”
condition. If the unit detects no problems, no mis-orientation, and no mis- configuration, it will arm
both of the event timers and transition immediately into Launch Detect Mode.
If the PET2+ detects an error during Verification Mode it will NOT transition into Launch Detect mode.
Instead it will sound an alarm tone (buzz) and continuously chirp and flash YELLOW with an ERROR
CODE to indicate what specific error condition was detected. DO NOT MISTAKE AN ERROR CODE
CONDITION for flight readiness and valid continuity feedback and inadvertently launch your rocket.
The error codes are as follows:
Error Code Error Condition
1 X-axis triggering and off-axis or off-cal limit
2 Y-axis triggering and off-axis or off-cal limit
3 Z-axis triggering and off-axis or off-cal limit
4 Auto-axis detection and no valid axis/orientation detected
5 Breakwire triggering with initial open circuit
Launch Detect mode
When all previous modes are complete, the unit transitions into launch detect mode. The piezo and
the GREEN LED indicate the continuity status of the Event 1 and Event 2 output terminals every
second as follows:
Status Code Status Condition
1 Long Beep/Flash No continuity on Event1 or Event 2 outputs
1 Short Beep/Flash Continuity on Event 1 output only
2 Short Beeps/Flashes Continuity on Event 2 output only
3 Short Beeps/Flashes Continuity on both Event 1 and Event 2 outputs
The unit also monitors the accelerometer and/or Breakwire input in order to determine the launch of
the rocket. After this event, the unit transitions into timing operation mode.
Page 2

Post Timing Mode
When in Post Timing Mode, the LED will flash slowly in YELLOW (≈2Hz). The unit will continue in this
mode until it is powered off. Keep in mind that if either timer has been configured in “repeat” mode,
the repeat timing cycles are active during this mode.
Programming and Configuration
The PET2+ provides 2 independent and identical groups of setpoints for each timer. The Global
Setpoints are applied and used by both timers appropriately. All setpoint values are stored in
nonvolatile memory.
Accessing the Start Menu
To start the interactive operation of the PET2+, press and hold the SELECT pushbutton while
applying power to the unit. Release the pushbutton after you hear a brief chirp from the piezo. You’re
now running the Start Menu and displaying the first menu choice (SLOW FLASHING RED LED)
Start Menu Menu Navigation
To scroll to the next available choice in a menu, tap the SELECT pushbutton.
To make a choice in a menu, tap the ENTER pushbutton.
(note: a brief chirp acknowledges each button press).
Start Menu Options
All settings are accessed from the Start Menu. The available options are:
- Timer 1 Setpoint Menu Verify/Adjust all user setpoints for Timer 1.
- Timer 2 Setpoint Menu Verify/Adjust all user setpoints for Timer 2.
- Global Setpoints & Diags Verify/Adjust global setpoints or run PET2+ diagnostics
- Escape to Flight Mode Exit the Start Menu and return to normal flight mode
Setpoint Menu Navigation and Setpoint Adjustment
To scroll to the next available setpoint, tap the SELECT pushbutton.
To choose a setpoint, tap the ENTER pushbutton:
- LED will flash/chirp the current value of the setpoint.
- A pause of 5 seconds ensues, followed by the Setpoint LED indication.
- To change a setpoint, tap in a new value during the 5 second pause via ENTER
- To double check your new value, choose the current setpoint again via ENTER
Setpoint Nomenclature
The timer uses the following acronyms to define specific flight events that are used for timer
triggering. These acronyms are defined as follows.
MEIG Main Engine IGnition
This is the 1st trigger event that occurs upon ignition of the rocket’s main engine (or first stage) when
acceleration meets/exceeds the timer’s MEIG setpoint (2-5 G’s).
MECO Main Engine Cut-Off.
This is the 2nd trigger event that occurs upon burnout or cut-off of the rocket’s main engine when
acceleration falls below the +1G calibration point.
SEIG Second Engine IGnition.
This is the 3rd trigger event that occurs upon ignition of the rocket’s second engine (or second stage)
when acceleration meets/exceeds the SEIG setpoint (2-5 G’s).
SECO Second Engine Cut-Off.
This is the 4th trigger event that occurs upon burnout or cut-off of the rocket’s second engine when
acceleration falls below the +1G calibration point.
Page 3
Timer 1 / Timer 2 Setpoints
MEIG Trigger Level Inertial acceleration trigger level for the MEIG event.
It is adjustable between +2G’s and +5G’s of acceleration (represented by a value of 2 to 5).
This Must be set for MECO/SEIG/SECO triggers.
SEIG Trigger Level Inertial acceleration trigger level for the SEIG event.
It is adjustable between +2G’s and +5G’s of acceleration (represented by a value of 2 to 5).
Trigger Event Defines the inertial trigger event used to trigger the timer.
1 = MEIG trigger / 2 = MECO trigger / 3 = SEIG trigger / 4 = SECO trigger.
Trigger Integration Time Sustained minimum time for a valid trigger event.
This time is adjustable between 0.1 seconds to 3.0 seconds (0.1 sec increments / a value of 1 to 30).
The timer applies to either the Inertial or Breakwire trigger.
Breakwire Function Defines the interaction and use of the Breakwire Input.
1 - N/A Not Applicable / Breakwire input is not used.
2 - Exclusive Trigger / Breakwire input (no inertial triggering)
3 - Interlock Trigger Breakwire AND Inertial triggers are interlocked (both must be valid).
Timer Interval The timer value (1-100), used with the “Time Base” setpoint.
Time Base Defines the Timer Interval and Resolution.
1 - Fast (0.1 seconds / 0.1 to 10.0 seconds)
2 - Slow (1.0 seconds / 1 to 100 seconds)
3 - Extra Slow (2.0 seconds / 2 to 200 seconds)
Output Pulse Duration of the output event when energized.
This time is adjustable between 0.1 seconds to 3.0 seconds (0.1 sec increments / a value of 1 to 30).
Timer Operation Defines “one-shot” continuous repeat mode operation.
1 = One Shot operation / 2 = Repeat operation
NOTE: Setpoints can be initialized to Factory Defaults by pressing/holding both pushuttons
during a power-up (chirps and flashes LED). Release both buttons to complete the reset.
Global Setpoints and Diagnostics Menu
From this menu, you can access the PET2+ global setpoints. The unit can also be placed into various
modes to verify the basic operational integrity of the unit, including the continuity circuits and outputs.
Inertial Trigger Axis Determines the timer orientation and accelerometer axis for triggering.
This applies to both timers. The Trigger Axis setpoint is adjustable between 1 and 4 as follows:
1 = +X axis trigger / 2 = +Y axis trigger / 3 = +Z axis trigger / 4 = Auto Detect axis (+X,+Y, or +Z)
Off Axis/Cal Deviation Specify a deviation deadband to ensure rocket is vertical @ launch
Ensures verticality on the launch rail and validates calibration has not drifted in excess. The valid
range is from 1 to 10, with the default value of 5 representing ≈ ±20 degrees range. If the altimeter
fails this test, you will receive the error codes as outlined in the Modes of Operation section.
NOTE: Operating the unit in temperature extremes may cause the unit to drift outside of
nominal calibration limits and induce an Error Condition.
Page 4

Piezo Tone This setpoint controls the tone of the Piezo.
Useful when running multiple audible devices or when the higher 4KHz tone is hard to discern
1 = 4KHz tone (high tone) / 2 = 4KHz and 1250Hz DTMF tone (low tone)
Diagnostic Options
Input Test Mode This feature allows the user to verify the operation of the continuity input circuits. It
operates identical to launch detect mode. The Chirping/Flashing is as follows:
Long Beep/Flash No continuity on Event 1 or Event 2
1 Short Beep Continuity on Event 1 only
2 Short Beeps Continuity on Event 2 only
3 Short Beeps Continuity on Event 1 and Event 2
Output Test Mode This feature allows the user to manually activate the Event1 and Event 2 circuits.
When this diagnostic is selected, the piezo will emit a WARNING TONE for 5 seconds, and the LED
will flash rapidly in RED to alert the user that output test mode has been selected. After the warning
tone is complete, the unit is ARMED. Press the SELECT pushbutton to activate the EVENT1 output.
Press the ENTER pushbutton to activate the EVENT2 output.
Note: A useful accessory for testing the outputs are 12-volt DC panel lamps. The lamps will allow you
to observe the operation of the outputs without the use of pyrotechnic devices.
IMPORTANT: Always exercise caution if using live pyro charges in the output test mode.
Escape to Start Menu Exit the Diagnostics Menu and return to the Start Menu
IMPORTANT: After selecting the Input/Output Test Mode diagnostic feature, you must power
off the unit prior to flight, additional testing, or usage of the altimeter.
Accelerometer Orientation
The PET2+ can be flown in any one of three orientations for inertial triggering. This flexibility allows
the designer to utilize the rocket payload space in a more effective manner as opposed to the single
axis/axial orientation required by other timer systems.
Figure 2 - +X/+Y/+Z orientation of the PET2+ (referencing the airframe nose cone)
Battery and Power Source Considerations
The PET2+ is intended to be operated using a standard 9-volt alkaline battery, however because of its
wide voltage input range, battery packs from 3.7V to 10V are compatible.
IMPORTANT: Always load-test your battery prior to flight to ensure adequate power reserve for
reliable operation and ignition of the ejection charges. processor brown-out conditions, resulting in
recovery failure.
Page 5
To load-test a 9V battery, you will require a DC multimeter capable of measurement with a 10-amp
capability. A 9-volt top-shelf alkaline battery can easily source in excess of 5 amps. Briefly connect
the meter leads across the battery terminals to measure the DC current capacity. If the measurement
is close to or drops below 2 amps, do not use the battery. Nominal load during operation is about 6
ma; and during output firing, the unit can draw well over 1 amp with low current e-matches.
Wiring Diagram - Low Current e-matches
Figure 3 depicts the recommended wiring convention for PET2+. This configuration activates the
e-matches using the same battery that powers the microcontroller and accelerometer system. The
success of this configuration relies on the voltage remaining relatively stable when firing a low-current
e-match. If the voltage sags too low, this may result in a brown-out or other timing operation
malfunction.
Figure 3 - Recommended wiring convention for the PET2+
Wiring Diagram - High-Current/Dual-Battery
Figure 4 depicts the recommended high-current/dual-battery wiring convention for the PET2+. When
your timing system pyro events do require higher current, or if you want to configure the most robust
and reliable configuration, use the dual-battery configuration as shown. Ensure that the negative
sides of each battery are connected together to form a single common. Observe the proper output
terminal connections, using the (-) leg of the Event 1 and Event 2 outputs.
IMPORTANT: Never exceed 20V for the secondary pyro battery to avoid damaging the PET2+.
Figure 4 - High-Current Wiring Diagram for the PET2+
Page 6

Breakwire Circuit and Operation
When using the Breakwire circuit, always use a “dry contact” connection between the (+) and (-)
terminals. The Breakwire circuit uses the BATTERY VOLTAGE to operate. The PET2+ uses the
Breakwire circuit for trigger operation by detecting when the circuit is OPEN. When used in your timer
triggering scheme, the Breakwire circuit must be CLOSED initially on the pad when the PET2+ is
initialized, and subsequently open via some other external event or operation. The Breakwire circuit
and the ENTER Pushbutton operate in parallel to one another (a closed Breakwire circuit can be
simulated by pressing the Enter button).
Physical Mounting Dimensions
Figure 5 depicts the physical mounting requirements for the PET2+. 4/40 screw hardware is
recommended to mount the unit into the payload section of the rocket or through a rocket airframe.
Nylon standoffs or insulated neoprene washers are also recommended for mounting against a hard
back plate or sled. When designing your airframe, avionics bay and mounting the PET2+, ensure that
it is oriented in one of the three allowable orientations as depicted in Figure 2.
IMPORTANT: Inadequate sealing of the electronics bay or exposure of the electronics to
ejection charge heat, BP residue, or pressure will cause the PET2+ to malfunction.
IMPORTANT: Black powder residue is extremely corrosive to the circuit board and its
components. Always clean off any inadvertent residue immediately to avoid long-term damage
to the unit.
Figure 5 - Mounting and Dimensions for the PET2+
Operating Tips for Success
• Always pre-test your PET2+ as COMPLETELY as possible prior to every flight. This includes a test
of the inputs, outputs, and Breakwire system.
• Always pre-test your batteries before each flight and ensure they have adequate power capacity for
the anticipated worst case flight profile, including unplanned “on-the-pad” waiting time.
• Always pre-measure your deployment charge initiators. Measure them for a nominal resistance and
verify they are not shorted.
• Double check your timing configuration and your anticipated flight profile to ensure you’ll reach
adequate acceleration levels to properly trigger and initiate your timing sequences.
Page 7
• Be sure to familiarize yourself with the audible feedback operations of the PET2+, in particular its
Error Code and Continuity chirping sequences. The unit will not arm itself in an Error condition, and
launching your rocket will result in a failure of the timing operations of your flight. Likewise, ignoring
the validity of continuity feedback may produce a failed timing event.
• Flying in extreme hot or cold temperatures may cause drift of the inertial sensor such that an Error
Code condition may exist due to this drift exceeding the nominal inertial calibrations stored in the
MCU EEPROM. If this condition exists, you can widen the deadband setpoint value (Off Axis/Cal
Deviation) in order to satisfy the POST verification mode.
Example Usage of the PET2+
BASIC 2-stage Rocket
- Booster ignition via ground support system
- Booster separation via PET2+ Timer 1 (MECO trigger @ 0.1 seconds)
- Sustainer ignition via PET2+ Timer 2 (MECO trigger @ 1.0 seconds)
- Booster recovery by engine ejection / Sustainer recovery by Avionics
Advanced 2-stage Rocket
- Booster ignition via ground support system
- Booster separation via PET2+ Timer 1 (MECO trigger @ 0.1 seconds)
- Booster recovery via PET2+ Timer 2 (MECO trigger @ X seconds)
- Sustainer ignition via PET2+ Timer 2 (MECO trigger @ 1.0 seconds)
- Sustainer recovery by Avionics / Timer 2 apogee back (SECO + X seconds)
Advanced 2-stage Airstart Rocket
- Booster ignition via ground support system
- Airstart ignition via PET2+ Timer 1 (MECO trigger @ 2.0 seconds)
- Booster recovery via PET2+ Timer 2 (MECO trigger @ X seconds)
- Booster separation via PET2+ Timer 1 (MECO trigger @ 0.1.seconds)
- Sustainer ignition via PET2+ Timer 2 (MECO trigger @ 1.0 seconds) Page 8

Page 9/10

Product Warranty
Missile Works Corporation has exercised reasonable care in the design and manufacture of this
product and warrants the original purchaser that the PET2+ is free of defects and that it will operate at
a satisfactory level of performance for a period of one year from the original date of purchase. If the
system fails to operate as specified, then return the unit (or units) within the warranty period for repair
or replacement (at our discretion). The system must be returned by the original purchaser, and be
free of modification or any other physical damage which renders the system inoperable. Upon repair
of replacement of the unit, Missile Works Corporation will return the unit postage-paid to the original
purchaser.
Product Disclaimer and Limit of Liability
Because the use and application of this equipment are beyond our control, the purchaser or user
agrees to hold harmless Missile Works Corporation and their agents from any and all claims,
demands, actions, debts, liabilities, judgments, costs, and attorney fees arising out of, claimed on
account of, or in any manner predicated upon loss or damage to property of, or injuries to or the death
of any and all persons arising out of the use this equipment. Due to the nature of electronic devices,
and the application and environments for those devices, the possibility of failure can never be totally
ruled out. It is the responsibility of the purchaser or user of this equipment to properly test and
simulate the actual conditions under which the device is intended to be used to ensure the highest
degree of reliability and success.