Chief Delphi - Reading battery voltage in software

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RbtGal1351

12-02-2006 18:34

Reading battery voltage in software

Hi,

Is it possible for the software to read the battery voltage? (The main battery)
I know that the battery voltage is known, because you can read it on the OI. But can I access it in code, and how?

I tried searching ifirobotics and here but couldn't find anything, just references to the OI.

Thanks,
~Stephanie

Mark McLeod

12-02-2006 18:37

Re: Reading battery voltage in software

Look in ifi_aliases.h, line 300

Code:

#define battery_voltage         rxdata.rc_main_batt*15.64/256

#define backup_voltage         rxdata.rc_backup_batt*15.64/256

lkdjm

12-02-2006 19:41

Re: Reading battery voltage in software

Quote:

Originally Posted by Mark McLeod

Look in ifi_aliases.h, line 300

Code:

#define battery_voltage         rxdata.rc_main_batt*15.64/256

#define backup_voltage         rxdata.rc_backup_batt*15.64/256

cool, thanks

the_short1

13-02-2006 10:19

Re: Reading battery voltage in software

thanks! that will be handy, if battery is too slow then maybe limit max speed of motor / turn off conveyor automatically to favour drivign!

RbtGal1351

16-02-2006 03:01

Re: Reading battery voltage in software

thanks so much!

htwiz2002

28-01-2007 23:14

Re: Reading battery voltage in software

:yikes:Wait! What type of variable is it?!?! When I try to read it it outputs a number greater than 16k!
I'm building a terminal interface (for debugging) it outputs a really strange value when I do:

Code:

printf("%d",battery_voltage);

Can anyone help?:ahh:

Jared Russell

28-01-2007 23:38

Re: Reading battery voltage in software

Quote:

Originally Posted by htwiz2002 (Post 567287)

:yikes:Wait! What type of variable is it?!?! When I try to read it it outputs a number greater than 16k!
I'm building a terminal interface (for debugging) it outputs a really strange value when I do:

Code:

printf("%d",battery_voltage);

Can anyone help?:ahh:

It's a float.

htwiz2002

28-01-2007 23:47

Re: Reading battery voltage in software

Quote:

Originally Posted by Abwehr (Post 567299)

It's a float.

So the printf replacement is "%f" ? (just because I'd rather set it now rather than try to remember it when I work on the code tomorrow... :p

DanDon

28-01-2007 23:59

Re: Reading battery voltage in software

If I recall correctly the printf functions in our code don't support the %f sequence. If the decimal place does not matter to you, just cast the variable as an int when printing it out (i.e. (int)variable). If you do want the decimal places, do something like:

Code:

variabledeci = variable - (int)variable; 



variabledeci*=1000; 



printf("variable = %d.%03d", (int)variable, (int)variabledeci);

This stores the decimal portion of the variable in another one, then multiplies by 1000 to get the decimals in front of the decimal point, and then prints the whole thing out.

bear24rw

29-01-2007 00:49

Re: Reading battery voltage in software

Wrote this over the summer when playing around with the edu rc. It prints out a float

Code:

current_voltage = rxdata.rc_main_batt;                 // Store current voltage

        average_voltage += current_voltage;                // Add the current voltage to the average stack



        voltage_count++;                                                        // Increase the average stack count

        

        if (voltage_count == 39)                                              // If the stack is 40

        {

                average_voltage = (average_voltage / 40) * 0.038 + 0.05;        // Get the average and apply formula

                i = (int)average_voltage;                                                        // Truncate decimals

                i2 = (int) ((average_voltage - i) * 1000);                                // Subtract to get decimals only and then multiply by 1000

                printf("Average: %d.%d \n",i,i2);                                                // Print the two together to make it look like a decimal



                average_voltage = 0;                                                                        // Reset the stack

                voltage_count = 0;                                                                        // Rest the counter

        }

DanDon

29-01-2007 08:10

Re: Reading battery voltage in software

Quote:

Originally Posted by bear24rw (Post 567331)

Wrote this over the summer when playing around with the edu rc. It prints out a float

Code:

current_voltage = rxdata.rc_main_batt;         // Store current voltage

    average_voltage += current_voltage;        // Add the current voltage to the average stack



    voltage_count++;                            // Increase the average stack count

    

    if (voltage_count == 39)                          // If the stack is 40

    {

        average_voltage = (average_voltage / 40) * 0.038 + 0.05;    // Get the average and apply formula

        i = (int)average_voltage;                            // Truncate decimals

        i2 = (int) ((average_voltage - i) * 1000);                // Subtract to get decimals only and then multiply by 1000

        printf("Average: %d.%d \n",i,i2);                        // Print the two together to make it look like a decimal



        average_voltage = 0;                                    // Reset the stack

        voltage_count = 0;                                    // Rest the counter

    }

The only problem that I see with that is, if your voltage is let's say 8.004, I believe that the way you are printing the variables would print 8.4.

If I recall correctly %03d forces three digits to be printed, which using the above example, would display 8.004.

bear24rw

29-01-2007 16:27

Re: Reading battery voltage in software

Quote:

Originally Posted by dhoizner (Post 567404)

lol true, i had 03 in there but i thought it was a mistake so i took it out before i posted. Nice catch

Joel J

29-01-2007 16:40

Re: Reading battery voltage in software

I have an itchy finger that wants to change that alias to remove the float. Is this kosher? Would bad things happen?

htwiz2002

29-01-2007 17:27

Re: Reading battery voltage in software

Quote:

Originally Posted by dhoizner (Post 567404)

Alright! I'll try it and see what happens.
Thank you very much!

Shinigami2057

29-01-2007 22:27

Re: Reading battery voltage in software

Quote:

Originally Posted by Joel J. (Post 567621)

I have an itchy finger that wants to change that alias to remove the float. Is this kosher? Would bad things happen?

I don't see why they would, unless any code depends on it (which you would find out about very quickly :P)

If you want to be safe, you can just take advantage of the global nature of the rxdata struct to get at the raw data:

Code:



if( rxdata.rc_main_batt < 127 )

    printf("HAMMER TIME!\n");



typedef struct  {     /* begin rx_data_record structure */





  ...

  unsigned char rc_main_batt, rc_backup_batt;

  ...



} rx_data_record;

RyanN

20-10-2007 18:32

Re: Reading battery voltage in software

Quote:

Originally Posted by htwiz2002 (Post 567287)

:yikes:Wait! What type of variable is it?!?! When I try to read it it outputs a number greater than 16k!
I'm building a terminal interface (for debugging) it outputs a really strange value when I do:

Code:

printf("%d",battery_voltage);

Can anyone help?:ahh:

I'm having the same problem, and I cannot figure it out at all!!! I've contacted our main programmer, I tried the code earlier (which gave me a reading of 70), and I've looked over and over in the code.

Bomberofdoom

21-10-2007 05:21

Re: Reading battery voltage in software

Holy cow! I know it's possible (it sounds possible), but I never knew there was such a thing in the code. Thanks!

Qbranch

21-10-2007 13:07

Re: Reading battery voltage in software

I have, in the past, used the main battery voltage to formulaicly modify the multiplier on the P term in the PID for the wheel motors (rate control). Worked great!

Also have used it to make power limits on non-servo systems vary to have the same power output (mechanical) regardless of lower battery voltage.

I.e., 25% power limits that stay constant regardless of battery voltage.

-q

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