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Power Accessories
Power Expander,
Status Port
The Power Expander includes a Status port that can be connected to an Analog/Digital input on the VEX
Microcontroller. The VEX Microcontroller can use this data to calculate the approximate voltage of the battery
connected to the Power Expander. To determine this value, divide the Power Expander read-out as follows. The
examples are for a 10-bit result (maximum value of 1023). If using a compiler with 12-bit resolution (max value
of 4095), multiply the analog values and divisors by 4.
Power Expanders, no revision, Rev NC1, A or A1:
With PIC Microcontrollers, divide the analog port value by 70.8.
Example: The PIC analog value is 460. 460 / 70.8 = 6.5
6.5v is the current voltage of your Power Expander battery.
With Cortex Microcontrollers divide the analog port value by 45.6.
Example: The Cortex analog value is 297. 297 / 45.6 = 6.5
6.5v is the current voltage of your Power Expander battery.
(See errata)
Power Expanders of revision A2:
With PIC Microcontrollers, divide the analog port value by 155.
Example: The PIC analog value is 930. 930 / 155 = 6.0
6.0v is the current voltage of your Power Expander battery.
(See errata)
With Cortex Microcontrollers divide the analog port value by 70.
Example: The Cortex analog value is 455. 455 / 70 = 6.5
6.5v is the current voltage of your Power Expander battery.
Errata, Rev A and Rev A1 Power Expanders with Cortex:
Due to loading of the Cortex analog circuit, the Power Expander LED will blink red even though the
battery is good and the internal circuit breaker is not tripped. VEX Robotics can update Rev A and Rev
A1 Power Expanders to Rev A2. This will restore normal LED response.
Errata, Rev A2 Power Expanders with PIC:
NOTE: Analog values are valid over the range of 6.5v - 4.5v. Suggested threshold values are: above 974
is good (6.3v <= batt), between 851 - 973 is battery low (5.5v <= batt <= 6.3v) and below 851 is
battery critical (batt <= 5.5v)
If the value drops below 4.8v, the internal Circuit Breaker may have tripped.
LED Feedback
The Power Expander also incorporates an internal circuit breaker to prevent damage to the unit or connected
devices. Refer to the following LED status chart for more information. The Feedback LED provides the battery and
circuit breaker status of the unit.
Green
Yellow
Red
Slow Red Blink
Fast Green Blink
Fast Yellow Blink
Fast Red Blink
Power Expander •
2
continued
Battery Good
Battery Low
Battery Critical
Circuit breaker is tripped
Circuit breaker was tripped / Battery Good
Circuit breaker was tripped / Battery Low - Charge soon
Circuit breaker was tripped / Battery Critical - Charge Now
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