Mix unflavored gelatine and sugar in medium microwaveable bowl until well blended. Stir in soda. Let stand 3 min. or until gelatine is softened. Microwave on High 3 min. or until gelatine and sugar are dissolved, stirring after each minute. Pour into 8-inch square dish sprayed with cooking spray.
Refrigerate 25 to 30 min. or until set but not firm. Meanwhile, add boiling water to raspberry gelatin mixes in medium bowl; stir 2 min. until completely dissolved. Stir in cold water. Cool 15 min.
Pour raspberry gelatin gently over clear gelatine layer in dish. Refrigerate 1 hour or until firm. Cut into 36 squares; top with raspberries just before serving.