1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
|
#include <stdio.h>
#include <pigpio.h>
/*
Measure how long a capacitor takes to charge through a resistance.
A potentimeter is used to vary the resistance.
The time taken will be proportional to the resistance.
3V3 ----- Potentiometer --+-- Capacitor ----- Ground
|
+-- gpio
gcc -o pot_cap_charge pot_cap_charge.c -lpigpio -lpthread -lrt
sudo ./pot_cap_charge
*/
#define GPIO 25
#define MAX_READING 1000
static uint32_t rechargeTick = 0;
void callback(int gpio, int level, uint32_t tick)
{
static uint32_t smooth = 0;
static int reading = 0;
uint32_t raw;
if (level == 1) /* measure recharge time */
{
++reading;
if (rechargeTick)
{
raw = tick - rechargeTick; /* set in main */
if (raw < MAX_READING) /* ignore outliers */
{
/* smooth using 0.8 * smooth + 0.2 * raw */
smooth = (raw + (4 * smooth)) / 5;
printf("%d %d %d\n", reading, raw, smooth);
}
else
{
/* ignore outlier, set dot at fixed position */
printf("%d %d %d\n", reading, 40, smooth);
}
}
else
{
/* ignore reschedule, set dot at fixed position */
printf("%d %d %d\n", reading, 20, smooth);
}
}
}
int main (int argc, char *argv[])
{
uint32_t t1, t2;
int tDiff;
if (gpioInitialise()<0) return 1;
gpioSetAlertFunc(GPIO, callback); /* callback when GPIO changes state */
while (1)
{
gpioWrite(GPIO, PI_OFF); /* drain capacitor */
gpioDelay(200); /* microseconds */
t1 = gpioTick();
gpioSetMode(GPIO, PI_INPUT); /* start capacitor recharge */
t2 = gpioTick();
/* dump reading if rechargeTick not accurate to 3 micros */
if ((t2 - t1) < 3) rechargeTick = t1; else rechargeTick = 0;
gpioDelay(5000); /* microseconds, nominal 200 readings per second */
}
gpioTerminate();
}
|
