Jacobs, P. A.

University of Queensland eSpace

A microcontroller-based delay generator for predicting shock arrival in the X2
expansion tube.
Mechanical Engineering Report 2011/05
P. A. Jacobs
School of Mechanical Engineering
The University of Queensland.
February 8, 2012
Contents
1 Introduction 2
2 Hardware 3
3 Firmware 7
Abstract
This report describes the hardware and firmware for the custom-built timing box that synchronises the spectrometer with
the X2 expansion tunnel flow. The box monitors the pressure signals at two locations in the acceleration tube and then
predicts the time of arrival of the shock as it emerges from the acceleration tube into the test chamber. The output is a 5
volt (digital) pulse to let the spectrometer know when to record its data.
1
1 Introduction
The box, based on a small microcontroller, monitors the pressure signals at two locations close to the end of the acceleration
tube and then predicts the time of arrival of the shock as it emerges from the acceleration tube into the test chamber. The box
was built to support an experimental study [1] in which small shot-to-shot changes in shock speeds were making it difficult to
record spectral data from the flow immediately following the shock. It was decided to monitor the last two pressure sensors in
the acceleration tube make an estimate of the shock speed from the arrival times. A typical signal is shown in Fig.1. The time
between the shock arrival at the second pressure sensor and its arrival at the end of the tube is about 50 microseconds.
Figure 1: Raw pressure signal at sensor location AT6.
Configuration of the box is done via the serial-port connection. The firmware has built-in help and provides some guidance.
Once configured, the box may be “armed” and it then waits for the shock arrival at the upstream pressure sensor. The time
between arrival at the two pressure sensors is recorded as a count on the hardware timer. This timer is allowed to continue
running while the predicted count of the timer, on shock arrival at the end of the tube, is estimated and put into the compare
register. When this target count is reached the digital output signal is pulsed. Timer ticks are 62.5 ns so, allowing for a few
cycles of house-keeping, the precision of the output pulse is within one microsecond.
2
2 Hardware
The main components of the box are:
• High-pass filters and buffer amplifiers (with a gain of about 20) for each pressure signal.
• A PIC18F14K22 microcontroller [2] that performs the timing and overall coordination. To get a sufficiently fast response,
we make use of the hardware timers and comparators built into the microcontroller and do a simple calculation of the
required timer count.
• An ST232 level converter to get the UART connected to the serial port of an external computer.
3
FILE: REVISION:
DRAWN BY: PAGE OF
TITLE
PIC18F14K22
VDD1
RA52
RA43
RA34
RC55
RC46
RC37
RC68
RC79
RB710 RB6 11
RB5 12
RB4 13
RC2 14
RC1 15
RC0 16
RA2 17
RA1 18
RA0 19
VSS 20
U101
2
4
6
1
3
5
CONN_ICSP
+5V
Vss
2
1
CONN102
PGD
!MCLR
VDD
VSS
DATA
CLK
NCPGC
!MCLR
1N4148
10k
15pF
15pF
Vss
16MHz
470
330
330
MCU_RX
SIG_B
SIG_A
Vss
COUT1
CCP1
COUT2
MCU_TX
2
1
CONN103
RED LED
X2 Shock timer −− MCU
Peter Jacobs
100n
C12IN1−
C12IN2−
RX
TX
CCP1
COUT2
COUT1
ARM/!TRIG
4 7
0
Vss
2
1
NC
NC
NC
NC
NC
RESET
1 3
4
FILE: REVISION:
DRAWN BY: PAGE OF
TITLE
X2 Shock Timer −− Power and Communication
Peter Jacobs
+5V
Vss
2
1
CONN_POWER 1N4004
1N4004
1
210u
1
21u
IN OUT
7805
GND
1
2
3
U1
+9 to 12V
0V
ST232CN
C1+1
V+2
C1−3
C2+4
C2−5
V−6
T2OUT7
R2IN8 R2OUT 9
T2IN 10
T1IN 11
R1OUT 12
R1IN 13
T1OUT 14
GND 15
VCC 16
U2
+5V
2
1
3
CONN_RS232
Vss
100uH
100n
100n
100n
100n
100n
Vss
Vss
10RMCU_TX
MCU_RX
TX
RX
GND
NC
NC
NC
NC
32
5
FILE: REVISION:
DRAWN BY: PAGE OF
TITLE
X2 Shock Timer −− INPUT/OUTPUT Conditioning
Peter Jacobs
3
2
1
4
8
TL072
U201
2
1
CONN_A
100n 470 470
1M 5k
1N4148
22k
1k2
330
SIG_A
+5V
+5V
Vss
Vss
VssVssVss
100n
Vss
5
6
7
4
8
TL072
U201
2
1
CONN_B
100n 470 470
1M 5k
1N4148
22k
1k2
330
SIG_B
+5V
+5V
Vss
Vss
VssVssVss
100n
Vss
High−pass
Filter
Input protection
for opamp
Opamp is
actually
MCP6022
Vss Vss
+5V
CCP1
1N4148
1N4148
3303302
1
CONN_DIGITAL_OUT
Protection network
for MCU pin
3 3
6
3 Firmware
The firmware running within the microcontroller has been compiled with Microchip’s C18 compiler. The code uses quite a
few Microchip-specific definitions and, also, the peripheral hardware library that comes with the C18 compiler. In-circuit
programming was done via the MPLAB development environment.
// x2 shock t imer . c
// Deteck the passage o f a shock at two pre s su r e s en so r s spaces 500mm apart
// and output a TTL−l e v e l s i g n a l when the shock i s expected to have t r a v e l l e d
// a f u r t h e r 450mm.
//
// PJ
// September 2010
//
//−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
#de f i n e VERSION STRING ”0 .4 09−Oct−2010”
#inc lude ”p18f14k22 . h”
#inc lude <s t d i o . h>
#inc lude <s t r i n g . h>
#inc lude <usar t . h>
#inc lude <t imers . h>
#inc lude <de lays . h>
#inc lude <adc . h>
#inc lude <s t d l i b . h>
#inc lude < l im i t s . h>
#pragma con f i g FOSC = HS
#pragma con f i g PLLEN = ON
#pragma con f i g FCMEN = ON
#pragma con f i g IESO = ON
#pragma con f i g PWRTEN = ON
#pragma con f i g BOREN = OFF
#pragma con f i g WDTEN = OFF
#pragma con f i g MCLRE = ON
#pragma con f i g LVP = OFF
#pragma con f i g XINST = OFF
// A bu f f e r to conta in incoming text commands .
#de f i n e TEXT BUFFER SIZE 20
s t a t i c unsigned char t e x t b u f f e r [TEXT BUFFER SIZE ] ;
#de f i n e ACK 0x01
#de f i n e BS 0x08
#de f i n e CR 0x0D
#de f i n e LF 0x0A
7
#de f i n e EOT 0x04
#de f i n e ETX 0x03
#de f i n e RS232 DEBUG MESSAGES 1
// Crysta l f requency in Hz
#de f i n e F OSC (64000000L)
// Names f o r some hardware p ins
#de f i n e ARMLED (LATBbits .LATB6)
#de f i n e LED ON 1 ;
#de f i n e LED OFF 0 ;
void i n i t i a l i z e h a r dwa r e ( void ) ;
unsigned char set CVR value ( unsigned char s tep ) ;
void arm and wait ( void ) ;
void pu l s e output ( void ) ;
void d i s p l a y s e t t i n g s ( void ) ;
unsigned i n t time12 ;
unsigned i n t ext ra = 0 ;
unsigned i n t time23 ;
//−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
void i n i t i a l i z e h a r dwa r e ( void )
{
// Analogue p ins AN0 through AN4, and r e f e r e n c e vo l t ag e s Vss−−Vdd .
ADCON1 = 0b00001010 ;
// Set up d i g i t a l por t s .
ANSELbits .ANS2 = 0 ; // enable d i g i t a l bu f f e r on RA2
// Comparator 1 output on RA2
TRISA = 0b11111011 ;
LATA = 0 ;
// Port B has s e r i a l communication : TX on RB7 and RX on RB5
ANSELHbits .ANS11 = 0 ; // enable d i g i t a l bu f f e r on RB5
// ARMLED output on RB6
TRISB = 0b10111111 ;
LATB = 0 ;
// Comparator 2 output on RC4, compare match on RC5
TRISC = 0b11001111 ;
LATC = 0 ;
// Set up s e r i a l port f o r use v ia p o l l i n g ( not i n t e r r up t s ) .
// From page 69 o f the C−l i b r a r y guide , we have the f o l l ow i ng formula .
// baud−r a t e = F OSC / (16 ∗ ( spbrg + 1) )
# de f i n e BAUDRATE 38400
8
# de f i n e SET BRG ((F OSC/BAUDRATE/16) − 1)
OpenUSART( USART TX INT OFF & USART RX INT OFF & USARTASYNCHMODE &
USART EIGHT BIT & USART CONT RX & USART BRGH HIGH, SET BRG ) ;
// Comparator 1 , with input from C12IN1− and output on RA2
CM1CON0bits .C1OE = 1 ;
CM1CON0bits .C1POL = 1 ; // i nv e r t to get r i ght−way up
CM1CON0bits .C1SP = 1 ; // high speed
CM1CON0bits .C1R = 1 ; // non−i n v e r t i n g input comes from C1Vref
CM2CON1bits .C1RSEL = 0 ; // va r i ab l e vo l tage r e f e r e n c e
// i nv e r t i n g input comes from C12IN1−
CM1CON0bits .C1CH1 = 0 ; CM1CON0bits .C1CH0 = 1 ;
CM1CON0bits .C1ON = 1 ;
// Comparator 2 , with input from C12IN2− and output on RC4
CM2CON0bits .C2OE = 1 ;
CM2CON0bits .C2POL = 1 ; // i nv e r t to get r i ght−way up
CM2CON0bits .C2SP = 1 ; // high speed
CM2CON0bits .C2R = 1 ; // non−i n v e r t i n g input comes from C1Vref
CM2CON1bits .C2RSEL = 0 ; // va r i ab l e vo l tage r e f e r e n c e
// i nv e r t i n g input comes from C12IN2−
CM2CON0bits .C2CH1 = 1 ; CM2CON0bits .C2CH0 = 0 ;
CM2CON0bits .C2ON = 1 ;
// Comparator vo l tage r e f e r e n c e comes from f i x ed r e f e r e n c e vo l tage o f 1 .024V.
VREFCON0bits .FVR1S1 = 0 ; VREFCON0bits .FVR1S0 = 1 ;
VREFCON0bits .FVR1EN = 1 ;
whi l e ( ! VREFCON0bits .FVR1ST ) ; // wait u n t i l s t ab l e
VREFCON1bits . D1PSS1 = 1 ; VREFCON1bits . D1PSS0 = 0 ; // from FVR output
VREFCON1bits .D1NSS = 0 ; // from VSS
set CVR value ( 8 ) ; // s e t i t on a moderate va lue
VREFCON1bits .D1EN = 1 ; // turn i t on
} // end i n i t i a l i z e h a r dwa r e ( )
unsigned char set CVR value ( unsigned char s tep )
// Sets b i t s 5 : 0 in vo l tage−r e f e r e n c e con t r o l r e g i s t e r .
{
i f ( s tep > 31 ) s tep = 31 ; // maximum st ep s in R−l adder
VREFCON2 = step ;
Delay100TCYx (100 ) ; // Allow i t to s e t t l e .
r e turn step ;
}
void arm and wait ( void )
// Waits f o r the shock s i g n a l s and then s e t s an output
// at the expected a r r i v a l time in the te s t−s e c t i o n .
{
9
unsigned char low , high ;
// Set up t imer
T1CONbits .TMR1CS = 0 ; // t i c k s at FOSC/4
T1CONbits .RD16 = 1 ; // read a l l 16 b i t s at once
TMR1H = 0 ; TMR1L = 0 ;
ARMLED = LED ON;
// Wait f o r a r r i v a l at f i r s t transducer , then s t a r t t iming .
whi l e ( ! CM1CON0bits .C1OUT ) ;
T1CONbits .TMR1ON = 1 ;
// On a r r i v a l at second transducer , look at t imer and
// p r ed i c t t imer value f o r a r r i v a l at t e s t s e c t i o n .
whi l e ( ! CM2CON0bits .C2OUT ) ;
low = TMR1L; high = TMR1H;
time12 = ( ( ( unsigned i n t ) high ) << 8) | low ;
time23 = ( time12 ∗ 2) + extra ;
CCPR1H = ( unsigned char ) ( time23 >> 8 ) ; CCPR1L = ( unsigned char ) time23 ;
// Compare mode : i n i t i a l i z e CCP1 pin low , s e t output on compare match .
CCP1CON = 0b00001000 ;
PIR1bits .CCP1IF = 0 ;
T3CONbits .T3CCP1 = 0 ; // look at t imer 1
// On compare match , we expect shock to a r r i v e at t e s t s e c t i o n .
// Send our TTL s i g n a l ( a l r eady on CCP1) .
whi l e ( ! PIR1bits .CCP1IF ) ;
T1CONbits .TMR1ON = 0 ; // stop the t imer
ARMLED = LED OFF;
// Wait a whi l e and c l ean up .
Delay1KTCYx (100 ) ;
CCP1CON = 0 ; // Turn o f f compare module .
PIR1bits .CCP1IF = 0 ;
LATCbits .LATC5 = 0 ; // make sure that out output s i g n a l i s o f f .
}
void pu l s e output ( void )
// Used f o r manual output , v ia command .
{
ARMLED = LED ON;
LATCbits .LATC5 = 1 ;
Delay1KTCYx (100 ) ;
LATCbits .LATC5 = 0 ;
Delay10KTCYx (200 ) ;
ARMLED = LED OFF;
re turn ;
10
}void d i s p l a y s e t t i n g s ( void )
{
p r i n t f ( ( const f a r rom char ∗)” ext ra= %d ( extra de lay in counts , with 62 .5 ns/ count )\ r \n” , ext ra ) ;
p r i n t f ( ( const f a r rom char ∗)”VREFCON2= %d ( cv r e f s t ep s from 31 , over 1 .024V)\ r \n” , VREFCON2) ;
re turn ;
}
//−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
void main ( void )
{
s t a t i c unsigned char t e x t l e n g th ;
s t a t i c unsigned char cha rac t e r ;
unsigned char i , v ;
char sma l l t e x t [ 1 0 ] ;
// Let ’ s begin . . .
i n i t i a l i z e h a r dwa r e ( ) ;
ARMLED = LED ON;
Delay10KTCYx (200 ) ;
ARMLED = LED OFF;
whi l e ( BusyUSART() ) ;
p r i n t f ( ( const f a r rom char ∗) ”\ r \nX2 shock speed t imer ” ) ;
p r i n t f ( ( const f a r rom char ∗) VERSION STRING ) ;
p r i n t f ( ( const f a r rom char ∗) ”\ r \n” ) ;
whi l e ( 1 ) {
// Wipe t e x t b u f f e r c l ean .
f o r ( i = 0 ; i < TEXT BUFFER SIZE ; ++i ) t e x t b u f f e r [ i ] = 0 ;
t e x t l e n g th = 0 ;
// Accumulate cha ra c t e r s u n t i l we get a Carr iage−Return charac t e r .
# de f i n e ECHOCHARACTERS 1
whi l e ( 1 ) {
whi le ( !DataRdyUSART( ) ) ; // wait f o r a charac t e r to a r r i v e
cha rac t e r = ReadUSART( ) ;
i f ( cha rac t e r == BS && tex t l e n g th > 0 ) {
// wipe out the p r ev i ou s l y r e c e i v ed cha rac t e r
t ex t l eng th −−;
t e x t b u f f e r [ t e x t l e n g th ] = 0 ;
# i f ECHOCHARACTERS
whi le ( BusyUSART() ) ; putcUSART( charac t e r ) ; // echo the backspace cha rac t e r
# end i f
cont inue ;
}
i f ( ( cha rac t e r != CR) && ( t ex t l e n g th < TEXT BUFFER SIZE−1) ) {
// normal cha rac t e r
11
t e x t b u f f e r [ t e x t l e n g th ] = charac t e r ;
t e x t l e n g th++;
# i f ECHOCHARACTERS
whi le ( BusyUSART() ) ; putcUSART( charac t e r ) ; // echo the charac t e r
# end i f
} e l s e {
# i f ECHOCHARACTERS
putrsUSART( ( const f a r rom char ∗)”\ r \n” ) ;
# end i f
break ;
}
} // end whi l e
t e x t b u f f e r [ t e x t l e n g th ] = 0 ; // terminate with NUL char
i f ( t e x t l e n g th == 0 ) cont inue ; // must have r e c e i v ed a CR with no command text
// p r i n t f ( ( const f a r rom char ∗)”Command: %s \ r \n” , t e x t b u f f e r ) ;
i f ( ! strncmppgm2ram ( ( char ∗) t e x t bu f f e r , ( rom f a r char ∗)” s t a tu s ” ,6) ) {
putrsUSART( ( const f a r rom char ∗)” Firmware ve r s i on= ” ) ;
putrsUSART( ( const f a r rom char ∗)VERSION STRING) ;
putrsUSART( ( const f a r rom char ∗)”\ r \n ” ) ;
d i s p l a y s e t t i n g s ( ) ;
p r i n t f ( ( const f a r rom char ∗)”OK\ r \n ” ) ;
cont inue ;
}
i f ( ! strncmppgm2ram ( ( char ∗) t e x t bu f f e r , ( rom f a r char ∗)” he lp ” ,4) | |
! strncmppgm2ram ( ( char ∗) t e x t bu f f e r , ( rom f a r char ∗ )”?” ,1 ) ) {
putrsUSART( ( const f a r rom char ∗)” Ava i l ab l e commands are :\ r \n ” ) ;
putrsUSART( ( const f a r rom char ∗)” s t a tu s ( p ings device , r e tu rn s ve r s i on s t r i n g )\ r \n ” ) ;
putrsUSART( ( const f a r rom char ∗)” he lp ( or ? to get t h i s l i s t )\ r \n ” ) ;
putrsUSART( ( const f a r rom char ∗)” s e t c v r e f nn ( s e t comparator r e f e r e n c e vo l tage in s t ep s 0 . . 3 1 o f 1 .024V\ r \n ” ) ;
putrsUSART( ( const f a r rom char ∗)” s e t ext ra nnnn ( s e t ext ra count , in 62 .5 ns s t ep s \ r \n ” ) ;
putrsUSART( ( const f a r rom char ∗)” arm ( puts dev i ce in to wai t ing mode)\ r \n ” ) ;
putrsUSART( ( const f a r rom char ∗)” pu l s e (manual pu l s e output )\ r \n ” ) ;
putrsUSART( ( const f a r rom char ∗)”OK\ r \n ” ) ;
cont inue ;
}
i f ( ! strncmppgm2ram ( ( char ∗) t e x t bu f f e r , ( rom f a r char ∗)” s e t ” ,3) ) {
i f ( ! strncmppgm2ram ( ( char ∗)& t e x t b u f f e r [ 4 ] , ( rom f a r char ∗)” c v r e f ” ,5) ) {
v = a to i ( ( char ∗)& t e x t b u f f e r [ 1 0 ] ) ;
v = set CVR value (v ) ;
p r i n t f ( ( const f a r rom char ∗)” s e t t i n g c v r e f s tep to %d\ r \n” , v ) ;
p r i n t f ( ( const f a r rom char ∗)”VREFCON2= 0x%x\ r \n” , VREFCON2) ;
} e l s e i f ( ! strncmppgm2ram ( ( char ∗)& t e x t b u f f e r [ 4 ] , ( rom f a r char ∗)” ext ra ” ,5) ) {
ext ra = a t o i ( ( char ∗)& t e x t b u f f e r [ 1 0 ] ) ;
p r i n t f ( ( const f a r rom char ∗)” s e t t i n g ext ra ( count ) to %d\ r \n” , ext ra ) ;
} e l s e {
putrsUSART( ( const f a r rom char ∗)”\ r \nUnknown opt ion to s e t .\ r \n ” ) ;
12
cont inue ;
}
putrsUSART( ( const f a r rom char ∗)”OK\ r \n” ) ;
cont inue ;
}
i f ( ! strncmppgm2ram ( ( char ∗) t e x t bu f f e r , ( rom f a r char ∗)”arm” ,3) ) {
d i s p l a y s e t t i n g s ( ) ;
putrsUSART( ( const f a r rom char ∗)”Waiting f o r shock s i g n a l . . . \ r \n ” ) ;
arm and wait ( ) ;
p r i n t f ( ( const f a r rom char ∗)” time12= %d ( decimal )\ r \n” , time12 ) ;
p r i n t f ( ( const f a r rom char ∗)” time23= %d ( decimal )\ r \n” , time23 ) ;
putrsUSART( ( const f a r rom char ∗)”\ r \nOK\ r \n ” ) ;
cont inue ;
}
i f ( ! strncmppgm2ram ( ( char ∗) t e x t bu f f e r , ( rom f a r char ∗)” pu l s e ” ,5) ) {
putrsUSART( ( const f a r rom char ∗)”Manual pu l s e output . . . \ r \n ” ) ;
pu l s e output ( ) ;
putrsUSART( ( const f a r rom char ∗)”\ r \nOK\ r \n ” ) ;
cont inue ;
}
p r i n t f ( ( const f a r rom char ∗)”Unknown command : %s \ r \n” , t e x t b u f f e r ) ;
} // end whi l e
// We ac tua l l y don ’ t ever expect to l eave the whi l e loop ( un t i l power−o f f ) .
CloseUSART ( ) ; // never get t h i s f a r
} // end main
13
A second, smaller board has been made to simulate the shock signals. The left figure, below, shows the two simulated signals
generated by this board. The right figure shows the amplified signal-2 plus positive-going edge of the digital output pulse.
// s i g n a l g e n e r a t o r . c
//
// Bare−bones s i g n a l generato r f o r shock−speed t imer .
// This s imu la t e s the 10 km/ s shock pas s ing the two
// upstream pre s su r e s en so r s .
//
// PJ , 28−Sep−2010
#inc lude ”p18f14k22 . h”
#inc lude <de lays . h>
#pragma con f i g FOSC = IRC
#pragma con f i g PLLEN = OFF
#pragma con f i g FCMEN = ON
#pragma con f i g IESO = OFF
#pragma con f i g PWRTEN = ON
#pragma con f i g BOREN = OFF
#pragma con f i g WDTEN = OFF
#pragma con f i g MCLRE = ON
#pragma con f i g LVP = OFF
14
#pragma con f i g XINST = OFF
// Clock f requency in Hz
#de f i n e F OSC (16000000L)
#de f i n e OUT1 (LATBbits .LATB5)
#de f i n e OUT2 (LATBbits .LATB6)
void main ( void )
{
// I n i t i a l i z e hardware .
// In the c on f i g b i t s above , we have s e l e c t e d the i n t e r n a l
// high−speed o s c i l l a t o r , which d e f a u l t s to 1MHz.
OSCCON |= 0b01110000 ; // s e t IRFC<2:0> f o r 16MHz F OSC
ANSELHbits .ANS11 = 0 ; // enable d i g i t a l bu f f e r on RB5
TRISB = 0b10011111 ; // RB5, RB6 output
LATB = 0 ;
Delay10KTCYx ( 2 ) ;
// 50 microseconds = 200 i n s t r u c t i o n c y c l e s @ F OSC = 16 MHz
OUT1 = 1 ;
Delay10TCYx ( 2 0 ) ;
OUT2 = 1 ;
Delay10KTCYx (200 ) ;
OUT1 = 0 ;
OUT2 = 0 ;
whi l e ( 1 ) ; // hang around f o r e v e r
}
15
References
[1] C.M. Jacobs. Radiation in low density hypervelocity flows. PhD thesis, The University of Queensland, Brisbane, and E´cole
Centrale, Paris., 2011.
[2] Microchip. PIC18(L)F1XK22 data sheet: 20-pin flash microcontrollers with nano watt XLP technology. Technical Report
DS41365E, Microchip Technology Inc., www.microchip.com, 2011.
16


A microcontroller-based delay generator for predicting shock arrival in the X2 expansion tube

http://espace.library.uq.edu.au/view/UQ:321760/UQ321760_fulltext.pdf

A microcontroller-based delay generator for predicting shock arrival in the X2 expansion tube

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