How can i uncheck all checkboxes after click button(check selected phones) in angularjs?

Here i have added my code below.after Check selected phones button clicked how to uncheck all checked checkboxes pls some one help me out for this . Expectation: after button click all checkboxes should unchecked i have added fiddle also help me out

var myApp = angular.module('myApp',[]);

myApp.controller('MyCtrl', function($scope,$http) {
        $scope.selectedBrands = [];
  
  $scope.selectBrand = function(selectedphone) {
        // If we deselect the brand
        if ($scope.selectedBrands.indexOf(selectedphone.brandname) === -1) {
        // Deselect all phones of that brand
        angular.forEach($scope.phones, function(phone) {
        if (phone.brandname === selectedphone.brandname) {
                phone.selected = false;
        }
      });
    }
  }
  
  $scope.checkSelectedphones = function() {
        var modelNames = [];
        var jsonArr = [];
        var subModelArr = [];
        var aletrMsg = '';
        angular.forEach($scope.phones, function(phone) {
          if (phone.selected) {
            modelNames.push(phone);
            var found = jsonArr.some(function(el) {
              if (el.model === phone.brandname) {
                el.subModel.push(phone.modelname);
                return true;
              }
            });
    
            if (!found) {
              subModelArr.push(phone.modelname);
              jsonArr.push({
                model: phone.brandname,
                                brand :'Nokia',
                subModel: subModelArr,
                                city:'Noida',
                                
              });
              subModelArr=[];
            }
                        
          }
                  
        });
                console.log(modelNames.length);
                if(modelNames.length == 0)
                {
                alert(modelNames.length ? aletrMsg : 'No phones selected!');
                }else
                {
        console.log(jsonArr);
        
                
                
      }
 
}

$scope.phones = [{
    id: "986745",
    brandname: "Nokia",
    modelname: "Lumia 735 TS"
  }, {
    id: "896785",
    brandname: "Nokia",
    modelname: "Nokia Asha 230"
  }, {
    id: "546785",
    brandname: "Nokia",
    modelname: "Lumia 510"
  }, {
    id: "144745",
    brandname: "Samsung",
    modelname: "Galaxy Trend 840"
  }, {
    id: "986980",
    brandname: "Samsung",
    modelname: "Galaxy A5"
  }, {
    id: "586980",
    brandname: "Samsung",
    modelname: "Galaxy Note 4 Duos"
  }, {
    id: "986980",
    brandname: "Samsung",
    modelname: "Galaxy A5"
  }, {
    id: "586980",
    brandname: "Samsung",
    modelname: "Galaxy Note Duos"
  }, {
    id: "232980",
    brandname: "Htc",
    modelname: "Htc One X9"
  }, {
    id: "456798",
    brandname: "Htc",
    modelname: "Desire 820"
  }, {
    id: "656798",
    brandname: "Htc",
    modelname: "Desire 810S"
        }];
        
});

myApp.filter('unique', function() {
  return function(collection, keyname) {
    var output = [], 
        keys = [];

    angular.forEach(collection, function(item) {
      var key = item[keyname];
      if(keys.indexOf(key) === -1) {
        keys.push(key);
        output.push(item);
      }
    });

    return output;
  };
});

 <script type="text/javascript" src="http://ift.tt/1QxAVn1"></script>

<div ng-controller="MyCtrl">
  <button ng-click="checkSelectedphones()">
    Check selected phones
  </button>
  
  <div ng-repeat="phone in phones | unique:'brandname'">
    <label>
      <input type="checkbox" ng-true-value="'{{phone.brandname}}'" ng-false-value="''" ng-model="selectedBrands[$index]" ng-change="selectBrand(phone)">  
      {{phone.brandname}}
    </label>
  </div>
  
  <br>
  
  <div ng-repeat="brand in selectedBrands track by $index" ng-if="brand">
    {{brand}}
    <div ng-repeat="phone in phones" ng-if="phone.brandname === brand">
      <label>
        <input type="checkbox" ng-model="phone.selected" >  
        {{phone.modelname}}
         
      </label>
    </div>
  </div>
</div>

demo