From fb71edfb6bc0702aa2ee1cc73d0822bbc37674ad Mon Sep 17 00:00:00 2001
From: fishsoupisgood <github@madingley.org>
Date: Sun, 24 Jan 2021 09:23:12 +0000
Subject: working-ish sensor

---
 humidity_sensors/app/sht20.c | 121 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 121 insertions(+)
 create mode 100644 humidity_sensors/app/sht20.c

(limited to 'humidity_sensors/app/sht20.c')

diff --git a/humidity_sensors/app/sht20.c b/humidity_sensors/app/sht20.c
new file mode 100644
index 0000000..d6d648b
--- /dev/null
+++ b/humidity_sensors/app/sht20.c
@@ -0,0 +1,121 @@
+#include "project.h"
+
+#define SHT20_ADDRESS 0x40
+
+#define TRIGGER_TEMP_MEASURE_HOLD             0xE3
+#define TRIGGER_HUMD_MEASURE_HOLD             0xE5
+#define TRIGGER_TEMP_MEASURE_NOHOLD           0xF3
+#define TRIGGER_HUMD_MEASURE_NOHOLD           0xF5
+#define WRITE_USER_REG                        0xE6
+#define READ_USER_REG                         0xE7
+#define SOFT_RESET                            0xFE
+
+
+void
+sht20_reset (void)
+{
+
+  i2cb_start_transaction (SHT20_ADDRESS, I2C_WRITE);
+  i2cb_send_data (SOFT_RESET);
+  i2cb_stop();
+  delay_ms (100);
+  printf ("$SNTHR\n");
+}
+
+
+char *
+sht20_temp_s (void)
+{
+  u8 h, l, c, s;
+  s32 t, tf;
+  float f;
+  static char ret[8];
+
+  i2cb_start_transaction (SHT20_ADDRESS, I2C_WRITE);
+  i2cb_send_data (TRIGGER_TEMP_MEASURE_NOHOLD);
+  delay_ms (100);
+  i2cb_start_transaction (SHT20_ADDRESS, I2C_READ);
+
+  h = i2cb_read (0);
+  l = i2cb_read (0);
+  c = i2cb_read (1);
+
+  i2cb_stop();
+
+  t = h;
+  t <<= 8;
+  t |= l & 0xfc;
+
+  f = t;
+  f /= 65536.;
+  f *= 175.72;
+  f -= 46.85;
+
+  f *= 100.;
+
+  t = (s32) (f + .5);
+
+  ret[0] = '-';
+
+  if (t >= 0)
+    s = 1;
+  else {
+    s = 0;
+    t = -t;
+  }
+
+  tf = t % 100;
+  t = t / 100;
+
+  sprintf (&ret[1], "%ld.%02ld", t, tf);
+
+  return &ret[s];
+
+}
+
+char *
+sht20_humid_s (void)
+{
+  u8 h, l, c;
+  u32 t, tf;
+  float f;
+  static char ret[8];
+
+  i2cb_start_transaction (SHT20_ADDRESS, I2C_WRITE);
+  i2cb_send_data (TRIGGER_HUMD_MEASURE_NOHOLD);
+  delay_ms (100);
+  i2cb_start_transaction (SHT20_ADDRESS, I2C_READ);
+
+  h = i2cb_read (0);
+  l = i2cb_read (0);
+  c = i2cb_read (1);
+
+  i2cb_stop();
+
+  t = h;
+  t <<= 8;
+  t |= l & 0xfc;
+
+  f = t;
+  f /= 65536.;
+  f *= 125.;
+  f -= 6.;
+
+  if (f < 0)
+    f = 0;
+
+  if (f > 100)
+    f = 100;
+
+  f *= 100.;
+
+  t = (u32) (f + .5);
+  tf = t % 100;
+  t = t / 100;
+
+  sprintf (ret, "%ld.%02ld", t, tf);
+
+
+  return ret;
+
+}
-- 
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