Reading battery voltage in software

[RbtGal1351]

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]

Look in ifi_aliases.h, line 300

#define battery_voltage	 rxdata.rc_main_batt*15.64/256
#define backup_voltage	 rxdata.rc_backup_batt*15.64/256

[lkdjm]

Originally Posted by Mark McLeod

Look in ifi_aliases.h, line 300

#define battery_voltage	 rxdata.rc_main_batt*15.64/256
#define backup_voltage	 rxdata.rc_backup_batt*15.64/256

cool, thanks

[the_short1]

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]

thanks so much!

[htwiz2002]

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:

printf("%d",battery_voltage);

Can anyone help?

[Jared Russell]

Originally Posted by htwiz2002

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:

printf("%d",battery_voltage);

Can anyone help?

It's a float.

[htwiz2002]

Originally Posted by Abwehr

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...

[DanDon]

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:

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]

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

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]

Originally Posted by bear24rw

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

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]

Originally Posted by dhoizner

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.

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]

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

[htwiz2002]

Originally Posted by dhoizner

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.

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

[Shinigami2057]

Originally Posted by Joel J.

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 )

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:

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;