1 /*
2 * Copyright (c) 2019 Vestas Wind Systems A/S
3 *
4 * SPDX-License-Identifier: Apache-2.0
5 */
6
7 #include <zephyr.h>
8 #include <device.h>
9 #include <drivers/adc.h>
10 #include <stdio.h>
11 #include <math.h>
12
13 #define LOG_LEVEL CONFIG_LOG_DEFAULT_LEVEL
14 #include <logging/log.h>
15 LOG_MODULE_REGISTER(main);
16
17 /* Nominal RTD (PT100) resistance in ohms */
18 #define RTD_NOMINAL_RESISTANCE 100
19
20 /* ADC resolution in bits */
21 #define ADC_RESOLUTION 24U
22
23 /* ADC maximum value (taking sign bit into consideration) */
24 #define ADC_MAX BIT_MASK(ADC_RESOLUTION - 1)
25
26 /* Bottom resistor value in ohms */
27 #define BOTTOM_RESISTANCE 2000
28
29 #ifndef CONFIG_NEWLIB_LIBC
sqrt(double value)30 static double sqrt(double value)
31 {
32 double sqrt = value / 3;
33 int i;
34
35 if (value <= 0) {
36 return 0;
37 }
38
39 for (i = 0; i < 6; i++) {
40 sqrt = (sqrt + value / sqrt) / 2;
41 }
42
43 return sqrt;
44 }
45 #endif /* CONFIG_NEWLIB_LIBC */
46
rtd_temperature(int nom,double resistance)47 static double rtd_temperature(int nom, double resistance)
48 {
49 const double a0 = 3.90802E-3;
50 const double b0 = -0.58020E-6;
51 double temp;
52
53 temp = -nom * a0;
54 temp += sqrt((nom * nom) * (a0 * a0) - 4.0 * nom * b0 *
55 (nom - resistance));
56 temp /= 2.0 * nom * b0;
57
58 return temp;
59 }
60
main(void)61 void main(void)
62 {
63 const struct device *lmp90100 = DEVICE_DT_GET_ONE(ti_lmp90100);
64 double resistance;
65 int32_t buffer;
66 int err;
67 const struct adc_channel_cfg ch_cfg = {
68 .channel_id = 0,
69 .differential = 1,
70 .input_positive = 0,
71 .input_negative = 1,
72 .reference = ADC_REF_EXTERNAL1,
73 .gain = ADC_GAIN_1,
74 .acquisition_time = ADC_ACQ_TIME(ADC_ACQ_TIME_TICKS, 0)
75 };
76 const struct adc_sequence seq = {
77 .options = NULL,
78 .channels = BIT(0),
79 .buffer = &buffer,
80 .buffer_size = sizeof(buffer),
81 .resolution = ADC_RESOLUTION,
82 .oversampling = 0,
83 .calibrate = 0
84 };
85
86 if (!device_is_ready(lmp90100)) {
87 LOG_ERR("LMP90100 device not ready");
88 return;
89 }
90
91 err = adc_channel_setup(lmp90100, &ch_cfg);
92 if (err) {
93 LOG_ERR("failed to setup ADC channel (err %d)", err);
94 return;
95 }
96
97 while (true) {
98 err = adc_read(lmp90100, &seq);
99 if (err) {
100 LOG_ERR("failed to read ADC (err %d)", err);
101 } else {
102 resistance = (buffer / (double)ADC_MAX) * BOTTOM_RESISTANCE;
103 printf("R: %.02f ohm\n", resistance);
104 printf("T: %.02f degC\n",
105 rtd_temperature(RTD_NOMINAL_RESISTANCE,
106 resistance));
107 }
108
109 k_sleep(K_MSEC(1000));
110 }
111 }
112
