Add impedance calculation functions from openBCI_NodeJS

Author: AJ Keller

Diff for: changelog.md

@@ -1,3 +1,9 @@
+# 0.0.9
+
+### New Features
+
+* Add impedance calculation functions from cyton
+
 # 0.0.8
 
 ### New Features

Diff for: openBCIUtilities.js

@@ -476,6 +476,54 @@ var utilitiesModule = {
     };
   },
   scaleFactorAux: SCALE_FACTOR_ACCEL,
+  /**
+   * Calculate the impedance
+   * @param sample {Object} - Standard sample
+   * @param impedanceTest {Object} - Impedance Object from openBCIBoard.js
+   * @return {null | Object} - Null if not enough samples have passed to calculate an accurate
+   */
+  impedanceCalculateArray: (sample, impedanceTest) => {
+    impedanceTest.buffer.push(sample.channelData);
+    impedanceTest.count++;
+
+    if (impedanceTest.count >= impedanceTest.window) {
+      let output = [];
+      for (let i = 0; i < sample.channelData.length; i++) {
+        let max = 0.0; // sumSquared
+        for (let j = 0; j < impedanceTest.window; j++) {
+          if (impedanceTest.buffer[i][j] > max) {
+            max = impedanceTest.buffer[i][j];
+          }
+        }
+        let min = 0.0;
+        for (let j = 0; j < impedanceTest.window; j++) {
+          if (impedanceTest.buffer[i][j] < min) {
+            min = impedanceTest.buffer[i][j];
+          }
+        }
+        const vP2P = max - min; // peak to peak
+
+        output.push(vP2P / 2 / k.OBCILeadOffDriveInAmps);
+      }
+      impedanceTest.count = 0;
+      return output;
+    }
+    return null;
+  },
+  impedanceTestObjDefault: (impedanceTestObj) => {
+    let newObj = impedanceTestObj || {};
+    newObj['active'] = false;
+    newObj['buffer'] = [];
+    newObj['count'] = 0;
+    newObj['isTestingPInput'] = false;
+    newObj['isTestingNInput'] = false;
+    newObj['onChannel'] = 0;
+    newObj['sampleNumber'] = 0;
+    newObj['continuousMode'] = false;
+    newObj['impedanceForChannel'] = 0;
+    newObj['window'] = 40;
+    return newObj;
+  },
   samplePacket: sampleNumber => {
     return new Buffer([0xA0, sampleNumberNormalize(sampleNumber), 0, 0, 1, 0, 0, 2, 0, 0, 3, 0, 0, 4, 0, 0, 5, 0, 0, 6, 0, 0, 7, 0, 0, 8, 0, 0, 0, 1, 0, 2, makeTailByteFromPacketType(k.OBCIStreamPacketStandardAccel)]);
   },

Diff for: package.json

@@ -1,6 +1,6 @@
 {
   "name": "openbci-utilities",
-  "version": "0.0.8",
+  "version": "0.0.9",
   "description": "The official utility package of Node.js SDK for the OpenBCI Biosensor Boards.",
   "main": "index.js",
   "scripts": {

Diff for: test/openBCIUtilities-test.js

@@ -1625,6 +1625,45 @@ $$$`);
       expect(openBCIUtilities.stripToEOTBuffer(totalBuf)).to.equal(null);
     });
   });
+  describe('#impedanceTestObjDefault', function () {
+    it('should give a new impedance object', function () {
+      const expectedImpedanceObj = {
+        active: false,
+        buffer: [],
+        count: 0,
+        isTestingPInput: false,
+        isTestingNInput: false,
+        onChannel: 0,
+        sampleNumber: 0,
+        continuousMode: false,
+        impedanceForChannel: 0,
+        window: 40
+      };
+      expect(openBCIUtilities.impedanceTestObjDefault()).to.deep.equal(expectedImpedanceObj);
+    });
+  });
+  describe('#impedanceCalculateArray', function () {
+    const numberOfChannels = k.OBCINumberOfChannelsDefault;
+    const newRandomSample = openBCIUtilities.randomSample(numberOfChannels, k.OBCISampleRate250, false, 'none');
+
+    afterEach(() => bluebirdChecks.noPendingPromises());
+
+    it('should not produce an array of impedances till window', function () {
+      const impTestObj = openBCIUtilities.impedanceTestObjDefault();
+      for (let i = 0; i < impTestObj.window - 1; i++) {
+        expect(openBCIUtilities.impedanceCalculateArray(newRandomSample(i), impTestObj)).to.equal(null);
+      }
+      expect(impTestObj.buffer.length).to.equal(impTestObj.window - 1);
+    });
+    it('should produce and array of impedances at window', function () {
+      const impTestObj = openBCIUtilities.impedanceTestObjDefault();
+      let impedanceArray = null;
+      for (let i = 0; i < impTestObj.window; i++) {
+        impedanceArray = openBCIUtilities.impedanceCalculateArray(newRandomSample(i), impTestObj);
+      }
+      expect(impedanceArray.length).to.equal(numberOfChannels);
+    });
+  });
 });
 
 describe('openBCIGanglionUtils', function () {