3.a.09. Command 212: Set Number of Current Sense Samples in Averages

Effect: This setting determines how many current sense samples will be in each motor’s current average. These averages are what the Get Currents command (216—Section 3.a.12)) returns. Each motor’s current average is a running average that is updated every other ADC conversion. The ADC can perform conversions at approximately 10 kHz, which means each motor’s current average is updated at approximately 5 kHz. The previous X samples are stored in memory, and the average returned is the average of those X most recent samples. This setting determines the value of X. The values are sent as three-bit, base-two exponents, meaning that the largest sample size allowed per average is 2⁷ (128) while the smallest is 2⁰ (1).

It is important to note that current sensing is not possible in joint motor mode. As such, this command has no effect when running in joint motor mode. It is also important to note that current sensing is only possible when using a motor driver daughter board that has VNH2SP30s (the VNH3SP30 does not provide current sense feedback).

This command does not save this setting to EEPROM, however it can be saved by issuing separate EEPROM-write commands (240—Section 3.d.02) that store the values at the appropriate addresses (3 for motor 1, 4 for motor 2). The values stored in EEPROM should be the actual number of samples to average, not the exponents. For example, if you are sending an exponent of 5 for motor 1 to the mega168 via this command, you should send a value of 2⁵ (32) to be stored in byte 3 of the mega168’s EEPROM. The value you store must be a power of two.

Values sent: motor 1 current sense samples exponent (3 bits), motor 2 current sense samples exponent (3 bits)

command byte = 212

data byte = (motor 2 current sense samples exponent << 3) | motor 1 current sense samples exponent