Sending more than 8 bits using printf

Questions » Sending more than 8 bits using printf

Antoine Jouet

11 years, 2 months ago.

Hello,

i'm using a mbed ship in order to get a analogic signal from a weight sensor and then send it to a computer. I can get the value with the function read (between 0 and 1), and then multiply it per 3.3 and convert it into 4 digital numbers (ex: 2.214 V).

I put my 4 values (2 2 1 4) on a table and I send this table with a pc.printf("%s",tab); Tab is 8 char sized, and sent through the USB port.

On the computer side, I get this data thanks to a library found on the interet, and it works pretty well (I print the datas "on live", as a graphic, point to point).

My problem is that I don't send the values from the mbed to the PC. I send about 150 points/sec and I would need about 1000, at least.

I read that I can't send more than 8 bits of data per printf, so i can't more than 2 points (4*2).

That's why I'm looking for a way to: -Make the number of printf/sec higher -Make possible to send about 15 points, so a 60 char sized table through a printf using %s

Thanks a lot for your answers, and please excuse me if there is a few English mistakes again.

Antoine

2 Answers

Erik -

11 years, 2 months ago.

You can send more than 8-byte with printf, you cant send more than 8-bit with putc, since that sends a single byte, which is 8 bit.

If you want to send it in that format I would just use %f: pc.printf("%1.3f\n", yourvalue);

However it depends on your exact code, but I expect your current problem to be due to simply the speed of your serial connection. Set a higher baud rate using pc.baud, and put the same value in the serial program you use on your computer. Then you can send your data alot faster.

Antoine Jouet

poster

11 years, 2 months ago.

Thanks for your answer. However, I can't change the baudrate, it create mistakes and I don't know why. Of course pc.baud(19200) works for exemple, but even if i put the same value on the computer side, i can't receive the datas properly.

I stille can't send more than about 3 points per printf, because the computer, or the connection "miss" more than half of the points, wich is annoying... That's wired.

Here's my code, if it can help:

include the mbed library with this snippet

while(1)
{
                for(i=0;i<16;i+=4)      //For 4 points with 4 numbers/points
                {
                    V=capteur.read();    //read my sensor
                    wait(0.001);
                    
                    W=3300*V;                        //get the first number
                    tab[i]=(W/1000)+48;          //second one, etc...
                    tab[i+1]=((W/100)%10)+48;
                    tab[i+2]=(((W/10)%100)%10)+48;
                    tab[i+3]=((((W/1)%1000)%100)%10)+48;   
                }
                tab[16]=0;       //put a 0 at the end

                pc.printf("%s",tab);
                wait(0.005);

   }

Using %f is still the easiest solution, but you seem to have a different problem. It really should work with higher baudrates, I have used baudrates up to 1mbps without any issues. I guess your printf problem is related to that. Have you tried using a different terminal program? Or maybe got another mbed you can test it on?

Anyway you need a higher baudrate for sure, it simply isnt possible with 9600 baudrate to meet your requirements. Putting more in a single printf won't result in a higher speed, that stays pretty much the same.

posted by Erik - 01 Mar 2013

Antoine Jouet

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