Unformatted data and single type variable

Hi all,
I have this problem, I have some numeric data to write in a file. I receive this data as a string from a device and then, I use the statements

Open path For Binary As #nFile
Put #nFile, , data
Close #nFile

to save these data.

Now, I'd rather to convert this string (19 bytes) having numeric data, in a single type variable (just 4 bytes).
What I figured out is that I can't because when I do it, in the text file I have some ASCII characters and I don't even know if there is some criteria in these characters.

Well, my question is, how can I write in a file, using the unformatted (binary) data and in the same time the single type variable?

Thanks to all in advance for your time.