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--- wind_sensor:meeting_minutes_may_19_2017 [2017/05/20 00:29]
mwu created
+++ wind_sensor:meeting_minutes_may_19_2017 [2021/09/19 21:59] (current)
@@ Line 5: / Line 5: @@
 =====Ultrasonic Wind Sensor=====
   * Updates:
-    * Implemented non-inverting amplifier with DC bias. Currently attempting to send just one pulse, so using a gain of about 110 V/V.
+    * Implemented non-inverting amplifier with DC bias. Currently attempting to send just one pulse, so using a gain of about 110 V/V. {{ :wind_sensor:one_pulse_amplifier.jpg?direct&600 |}}
+      * The disadvantage to having this amplifier is that the noise is also amplified which causes the voltage comparator to trigger falsely.
+    * Attempted to use the Schmitt Trigger to "qualify" the signal before registering it as a valid response.
+      * The trigger's threshold levels were experimentally determined to be: Vth = 1.95V, Vtl = 1.15V. The idea was to center the signal at one of the thresholds and use the other threshold as the trigger. This would've solved the issue since the signal would have to satisfy one threshold before it changes the output of the trigger (qualification).
+      * The signal was centered at 1.95V, but the result was inconsistent. Sometimes the signal would register while other times it wouldn't.
+    * Since the Schmitt Trigger didn't work out, we did a bit of research to see if we could add hysteresis to our LM339 voltage comparator. We could and we did, and the results were more consistent.
+      * This worked okay, but the results we obtained were not as consistent as we would've liked (~1 us variance). After observing the output of the LM339 chip with hysteresis on the oscilloscope, we discovered that the time of transition changes by a period or so. We need to investigate this further to improve the consistency of the triggering.
   * To Do:
+    * Test reducing ringing by sending half-period shifted pulses after the initial set of pulses.
+    * Investigate how to improve the reliability of the LM339 with hysteresis triggering mechanism.
+    * Conduct tests with fans and add in calculation of the wind speed into the program so it can print out the derived wind speed directly onto the console.