2 * Copyright © 2012 Keith Packard <keithp@keithp.com>
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; version 2 of the License.
8 * This program is distributed in the hope that it will be useful, but
9 * WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 * General Public License for more details.
13 * You should have received a copy of the GNU General Public License along
14 * with this program; if not, write to the Free Software Foundation, Inc.,
15 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
26 * Barometer calibration
28 * We directly sample the barometer. The specs say:
30 * Pressure range: 15-115 kPa
31 * Voltage at 115kPa: 2.82
32 * Output scale: 27mV/kPa
34 * If we want to detect launch with the barometer, we need
35 * a large enough bump to not be fooled by noise. At typical
36 * launch elevations (0-2000m), a 200Pa pressure change cooresponds
37 * to about a 20m elevation change. This is 5.4mV, or about 3LSB.
38 * As all of our calculations are done in 16 bits, we'll actually see a change
39 * of 16 times this though
41 * 27 mV/kPa * 32767 / 3300 counts/mV = 268.1 counts/kPa
44 /* Accelerometer calibration
46 * We're sampling the accelerometer through a resistor divider which
47 * consists of 5k and 10k resistors. This multiplies the values by 2/3.
48 * That goes into the cc1111 A/D converter, which is running at 11 bits
49 * of precision with the bits in the MSB of the 16 bit value. Only positive
50 * values are used, so values should range from 0-32752 for 0-3.3V. The
51 * specs say we should see 40mV/g (uncalibrated), multiply by 2/3 for what
52 * the A/D converter sees (26.67 mV/g). We should see 32752/3300 counts/mV,
53 * for a final computation of:
55 * 26.67 mV/g * 32767/3300 counts/mV = 264.8 counts/g
57 * Zero g was measured at 16000 (we would expect 16384).
58 * Note that this value is only require to tell if the
59 * rocket is standing upright. Once that is determined,
60 * the value of the accelerometer is averaged for 100 samples
61 * to find the resting accelerometer value, which is used
62 * for all further flight computations
65 #define GRAVITY 9.80665
68 * Above this height, the baro sensor doesn't work
70 #define AO_MAX_BARO_HEIGHT 12000
73 * Above this speed, baro measurements are unreliable
75 #define AO_MAX_BARO_SPEED 200
77 #define ACCEL_NOSE_UP (ao_accel_2g >> 2)
80 * Speed and acceleration are scaled by 16 to provide a bit more
81 * resolution while still having reasonable range. Note that this
82 * limits speed to 2047m/s (around mach 6) and acceleration to
83 * 2047m/s² (over 200g)
86 #define AO_M_TO_HEIGHT(m) ((int16_t) (m))
87 #define AO_MS_TO_SPEED(ms) ((int16_t) ((ms) * 16))
88 #define AO_MSS_TO_ACCEL(mss) ((int16_t) ((mss) * 16))
90 extern __pdata uint16_t ao_sample_tick; /* time of last data */
91 extern __pdata int16_t ao_sample_pres; /* most recent pressure sensor reading */
92 extern __pdata int16_t ao_sample_alt; /* MSL of ao_sample_pres */
93 extern __pdata int16_t ao_sample_height; /* AGL of ao_sample_pres */
94 extern __data uint8_t ao_sample_adc; /* Ring position of last processed sample */
97 extern __pdata int16_t ao_sample_accel; /* most recent accel sensor reading */
100 extern __pdata int16_t ao_ground_pres; /* startup pressure */
101 extern __pdata int16_t ao_ground_height; /* MSL of ao_ground_pres */
104 extern __pdata int16_t ao_ground_accel; /* startup acceleration */
105 extern __pdata int16_t ao_accel_2g; /* factory accel calibration */
106 extern __pdata int32_t ao_accel_scale; /* sensor to m/s² conversion */
109 void ao_sample_init(void);
111 /* returns FALSE in preflight mode, TRUE in flight mode */
112 uint8_t ao_sample(void);
118 #define to_fix16(x) ((int16_t) ((x) * 65536.0 + 0.5))
119 #define to_fix32(x) ((int32_t) ((x) * 65536.0 + 0.5))
120 #define from_fix(x) ((x) >> 16)
122 extern __pdata int16_t ao_height; /* meters */
123 extern __pdata int16_t ao_speed; /* m/s * 16 */
124 extern __pdata int16_t ao_accel; /* m/s² * 16 */
125 extern __pdata int16_t ao_max_height; /* max of ao_height */
126 extern __pdata int16_t ao_avg_height; /* running average of height */
128 extern __pdata int16_t ao_error_h;
129 extern __pdata int16_t ao_error_h_sq_avg;
132 extern __pdata int16_t ao_error_a;
135 void ao_kalman(void);
137 #endif /* _AO_SAMPLE_H_ */