add SDI-12 spy

Signed-off-by: Sara Damiano <sdamiano@stroudcenter.org>

tools/SDI12_spy/SDI12_spy.ino

@@ -0,0 +1,56 @@
+/**
+ * @file h_SDI-12_slave_implementation.ino
+ * @copyright (c) 2013-2020 Stroud Water Research Center (SWRC)
+ *                          and the EnviroDIY Development Team
+ *            This example is published under the BSD-3 license.
+ * @date 2016
+ * @author D. Wasielewski
+ *
+ * @brief Example H:  Using SDI-12 in Slave Mode
+ *
+ * Example sketch demonstrating how to implement an arduino as a slave on an SDI-12 bus.
+ * This may be used, for example, as a middleman between an I2C sensor and an SDI-12
+ * datalogger.
+ *
+ * Note that an SDI-12 slave must respond to M! or C! with the number of values it will
+ * report and the max time until these values will be available.  This example uses 9
+ * values available in 21 s, but references to these numbers and the output array size
+ * and datatype should be changed for your specific application.
+ *
+ * D. Wasielewski, 2016
+ * Builds upon work started by:
+ * https://github.com/jrzondagh/AgriApps-SDI-12-Arduino-Sensor
+ * https://github.com/Jorge-Mendes/Agro-Shield/tree/master/SDI-12ArduinoSensor
+ *
+ * Suggested improvements:
+ *  - Get away from memory-hungry arduino String objects in favor of char buffers
+ *  - Make an int variable for the "number of values to report" instead of the
+ *    hard-coded 9s interspersed throughout the code
+ */
+
+#include <SDI12.h>
+
+#define DATA_PIN 7 /*!< The pin of the SDI-12 data bus */
+
+// Create object by which to communicate with the SDI-12 bus on SDIPIN
+SDI12 slaveSDI12(DATA_PIN);
+
+void setup() {
+  Serial.begin(115200);
+  slaveSDI12.begin();
+  delay(500);
+  slaveSDI12.forceListen();  // sets SDIPIN as input to prepare for incoming message
+  Serial.println("Starting SDI-12 Spy");
+}
+
+void loop() {
+  while (slaveSDI12.available()) {
+    int readChar = slaveSDI12.read();
+    Serial.write(readChar);
+    // if (readChar == '\n') {
+    //   slaveSDI12.forceListen();
+    // } else {
+    //   delay(10);// 1 character ~ 7.5ms
+    // }
+  }
+}