nsstring to nsdata

-(NSData*) hexToBytes {

    NSMutableData* data = [NSMutableData data];

    int idx;

    NSString * tempString = @"AA4400000029000409AA9D616A4B3A5C40111D3C139A24263C402209E4BA91E6A284E8B0B72801308AC9C6C0C8533A0130EA";

    for (idx = 0; idx+2 <= tempString.length; idx+=2) {

        NSRange range = NSMakeRange(idx, 2);

        NSString* hexStr = [tempString substringWithRange:range];

        NSScanner* scanner = [NSScanner scannerWithString:hexStr];

        unsigned intValue;

        [scanner scanHexInt:&intValue];

        [data appendBytes:&intValue length:1];

    }

    return data;

}