Initial commit

README.md

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+### Petsound
+[Petsound](https://www.discogs.com/release/2557998-The-Beach-Boys-Pet-Sounds) is a pillow or plush toy that makes a sound when you pet it. It has a velostat sheet that senses pressure, and we define "petting" as significant variaton of that pressure.
+
+#### [Video](https://tooot.im/@zvinj/113906516287736785)
+
+![Schematic diagram](petsound_bb.png)
+
+
+Pet detection is done by an arduino nano that sets and `ISD1820` sampling boards's `P-L` pin to high while petting is detected. The audio out of the board goes to a class D 2.5W audio amplifier.

petsound.ino

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+#define SENSORPIN A7
+#define OUTPIN 13
+#define DELAYMILLIS 50
+#define NSAMPLES 20
+#define MINCHANGE 13
+#define ON HIGH
+#define OFF LOW
+
+int samples[NSAMPLES] = {0};
+int index;
+
+void setup() {
+  pinMode(OUTPIN, OUTPUT);
+  Serial.begin(115200);
+  index = 0;
+}
+
+void loop() {
+  samples[index] = analogRead(SENSORPIN);
+  index = (index + 1) % NSAMPLES;
+  int maxlevel = -1;
+  int minlevel = 2000;
+  for (int i = 0; i < NSAMPLES; i++) {
+    if (samples[i] < minlevel) {
+      minlevel = samples[i];
+    }
+    if (samples[i] > maxlevel) {
+      maxlevel = samples[i];
+    }
+  }
+  Serial.println(maxlevel - minlevel);
+  digitalWrite(OUTPIN, (maxlevel - minlevel) > MINCHANGE ? ON : OFF);
+  delay(DELAYMILLIS);
+}