Designing An Electronic Trigger
Mechanism For A Paintball Marker To
Allow User Selectable Firing Rates
ECE 4884/4007
Fall 2007
Nathan Densmore
Matthew Roese
Andrew Adams
Chris Britton (Team Leader)
Overview
• Design and implement an
electronic trigger
• Upgrading is more practical
compared to other high end
electronic markers
• Target customers will be
scenario paintball
enthusiasts
• Principal expense is
development cost
Georgia Institute of Technology
ECE 4007 Fall 2007
Design Objectives
• Electronic trigger upgrade for the 98 Custom
paintball marker
• Two firing modes: semi-automatic and fully
automatic
• LCD screen will display the mode and selected rate of
fire
• LED indicator for low ammunition and selected firing
mode
• User friendly up/down buttons to select the rate of
fire
Georgia Institute of Technology
ECE 4007 Fall 2007
Design Approach
• Key component is PIC Microcontroller (16F690)
• Powered by 9V battery
• Trigger pressed will activate the micro switch allowing 9V
signal to energize the solenoid
• PIC will output to an LED indicating firing mode
• PIC will output to LCD module indicating firing mode and
rate
Georgia Institute of Technology
ECE 4007 Fall 2007
Top Level Design of Circuit
Components
3
Supply
VSS
VDD +5V
2
VSS
VDD +5V
2
LED
VDD +5V
Push Button
2
VSS
I/O
I/O
I/O
I/O
PIC
Microcontroller
8 or 4
I/O
I/O
Data Path
3
Control Inputs
I/O
LCD
Module
I/O
Push Button
2
VSS
VDD +5V
Trigger
Georgia Institute of Technology
ECE 4007 Fall 2007
2
VSS
VDD +9V
Solenoid
PIC Controller
•
•
•
•
•
•
20 pins – 1 VDD, 1 VSS, up to 18 I/O pins
Operates on 2.0-5.5V
Up to 20MHz oscillator/clock
Up to 200ns instruction cycle
8-bit and 16-bit timer/counters
FLASH/EEPROM – up to 100,000 writes
Georgia Institute of Technology
ECE 4007 Fall 2007
PIC Microcontroller
1
20
VSS - Supply
RA5 – LCD Enable Output
2
19
RA0 – Supply (Firing Mode) Input
RA4/CLKOUT – Solenoid Output
3
18
RA1 – Trigger Input
RA3 – LCD Read/Write Output
4
17
RA2 – LCD Register Select Output
RC5 – LCD Data Bit 5 Output
5
16
RC0 – LCD Data Bit 0 Output
RC4 – LCD Data Bit 4 Output
6
15
RC1 – LCD Data Bit 1 Output
RC3 – LCD Data Bit 3 Output
7
14
RC2 – LCD Data Bit 2 Output
RC6 – LCD Data Bit 6 Output
8
13
RB4 – LED Green Output
RC7 – LCD Data Bit 7 Output
9
12
RB5 – LED Red Output
RB7 – Pushbutton Down Input
10
11
RB6 – Pushbutton Up Input
PIC16F690
VDD - Supply
Georgia Institute of Technology
ECE 4007 Fall 2007
PIC Programming Environment
• MPLAB Integrated Development Environment (IDE)
included as tool to program PIC
• MPLAB is programmed in assembly language
• PIC Kit 2 software responsible for debugging code
and loading chip
Georgia Institute of Technology
ECE 4007 Fall 2007
Pseudo-code Example
Set BPS default; Set Ball Count;
When ROF switch  Semi or Full
LED
if Semi ROF  GREEN Solid
if Semi ROF  RED Solid
LCD
if Semi ROF  Display “Semi”
if Full ROF  Diplay “Full” and BPS
PUSHBTN
if Full ROF 
when UP PUSHBTN
 BPS + = 1
when DOWN PUSHBTN  BPS - = 1
when UP & DOWN  BPS = 0, Go to LED, LCD
Georgia Institute of Technology
ECE 4007 Fall 2007
Power Supply Schematic
Georgia Institute of Technology
ECE 4007 Fall 2007
Debounced Trigger Circuit
• “Beginning” of circuit, and activated when trigger is pulled
• Switch will send a high input to the PIC controller
Georgia Institute of Technology
ECE 4007 Fall 2007
Push Buttons (Up/Down)
•
•
•
UP and DOWN pushbuttons are inputs to the PIC; used only when in Full Auto
Mode
UP pushbutton will increase firing rate; DOWN will decrease firing rate
Both UP and DOWN selected simultaneously will RESET ball count
Georgia Institute of Technology
ECE 4007 Fall 2007
LED Mode Indicator
• Semi Mode:
Green LED
• Full Mode:
Red LED
• Low Ammo Status:
LED alternates
red and green
Georgia Institute of Technology
ECE 4007 Fall 2007
LCD Module
• Display numbers and words
• More versatile than 7segment LED
• Line length 8 characters
• 14 pins in order to interface
PIC controller
• 8 data lines, 3 control lines,
& 2 power lines
• Time delay between LCD
and PIC interface
2 - VDD
1- Ground
PIC
Georgia Institute of Technology
ECE 4007 Fall 2007
2
Enable
6
4
Read/Write
5
5
Data bit 5
12
6
Data bit 4
11
7
Data bit 3
10
8
Data bit 6
13
9
Data bit 7
14
14
Data bit 2
9
15
Data bit 1
8
16
Data bit 0
7
17
Register Select
4
LCD Module
Solenoid
• Powered by +9V
• PIC outputs +5V and closes
transistor circuit
• Current freely flows and fires the
solenoid
• PIC outputs 0V and opens
transistor circuit
• Current stops flowing and
solenoid returns to initial state
• Diode prevents residual current
from damaging transistor
Georgia Institute of Technology
ECE 4007 Fall 2007
Mechanical Operation
•
•
•
•
•
•
•
Operator pulls trigger
Trigger throws trigger switch
Solenoid fires and forces rod
upward
Rod rotates sear rocker pin and
releases bolt
Bolt spring sends bolt forward
inducing firing operation
Blowback resets bolt, locking
sear into initial position
Solenoid magnet resets
solenoid to initial position
Georgia Institute of Technology
ECE 4007 Fall 2007
Component Enclosure
• Plastic enclosure will
mount on marker’s
magazine
• Enclosure will house
all of the electronic
trigger assembly
Georgia Institute of Technology
ECE 4007 Fall 2007
Technical Advantages and
Disadvantages
• LCD module is more flexible than 7-segment
LED display
• Relatively inexpensive production cost
• Circuit components are easily replaceable98
• Circuit design larger than existing products
• LCD module is bulky
Georgia Institute of Technology
ECE 4007 Fall 2007
Marketing Advantages
• Ability to change firing modes quickly
• Able to change rate of fire efficiently
• Easy operator interface allows for quick selection of
system configurations
• LCD data display
• No special tool or manual to switch modes or firing rates
Georgia Institute of Technology
ECE 4007 Fall 2007
Cost Analysis
Design Cost
Purchased
Item Description
Quanity
Unit Price
Amount
Digi-Key Corporation
Resistor 4.7K Ω
6
0.15
0.90
Digi-Key Corporation
Resistor 1K Ω
1
0.15
0.15
Digi-Key Corporation
Resistor 150 Ω
2
0.15
0.30
Digi-Key Corporation
NPN Transistor
1
0.11
0.11
Digi-Key Corporation
2-In Nand Gate
2
0.56
1.12
Digi-Key Corporation
Rectifier GPP 50V
1
0.26
0.26
Digi-Key Corporation
Lever Switch
1
1.10
1.10
Digi-Key Corporation
Pushbutton Switch
2
3.04
6.08
Digi-Key Corporation
Rocker Switch
1
1.80
1.80
Digi-Key Corporation
Regulator
1
0.72
0.72
Digi-Key Corporation
Capacitor .1µF
1
0.11
0.11
Digi-Key Corporation
Capacitor .33µF
1
0.15
0.15
Digi-Key Corporation
9V Battery Lead
1
0.33
0.33
Digi-Key Corporation
LED Light
1
0.75
0.75
Digi-Key Corporation
8x1 LCD Module
1
24.24
24.24
Digi-Key Corporation
PIC16F57 28-DIP
1
1.55
1.55
Digi-Key Corporation
PIC16F628A 18-DIP
1
3.35
3.35
Digi-Key Corporation
PICKIT 2 Starter Kit
1
49.99
49.99
Adv. Paintball Electronics
Solenoid
1
19.95
19.95
Tippmann Parts
Bag of Parts for Trigger
1
16
16.00
Shipping Cost
16.96
Total Design Cost
145.92
Georgia Institute of Technology
ECE 4007 Fall 2007
Future Work
• Program the PIC microcontroller to fire
paintball marker (2 weeks)
• Design an etched circuit board for more
efficient production (1 week)
• Program PIC microcontroller to work with
LCD module (4 days)
• Assemble product and test on marker
(3 days)
Georgia Institute of Technology
ECE 4007 Fall 2007