The Maestro has three indicator LEDs:
- The green USB LED indicates the USB status of the device. When the Maestro is not connected to a computer via the USB cable, the green LED will be off. When you connect the Maestro to USB, the green LED will start blinking slowly. The blinking continues until the Maestro receives a particular message from the computer indicating that the Maestro’s USB drivers are installed correctly. After the Maestro gets this message, the green LED will be on, but it will flicker briefly when there is USB activity. The control center application constantly streams data from the Maestro, so when the control center is running and connected to the Maestro, the green LED will flicker constantly.
- The red error/user LED usually indicates an error. The red LED turns on when an error occurs, and turns off when the error flags have been cleared. See Section 4.b for more information about errors. The red LED can also be controlled by the user script; the red LED will be on if there is an error or if the script command for turning it on was run.
- The yellow status LED indicates the control status. When the Maestro is in auto-baud detect mode (the default) and has not yet detected the baud rate, the yellow LED will blink slowly. During this time the Maestro does not transmit any servo pulses. Once the Maestro is ready to drive servos, the yellow LED will periodically flash briefly. The frequency of the flashes is proportional to the servo period (the amount of time between pulses on a single channel); with a period of 20 ms the flashing occurs approximately once per second. On the Micro Maestro, the number of flashes indicates the state: a single flash indicates that none of the servos are enabled (no pulses are being sent) and all output channels are low, while a double flash indicates that at least one of the servos is enabled or one of the output channels is being driven high. The Mini Maestros only emit single flashes. Also, when a valid serial command is received, the yellow LED will emit a brief, dim flash which ends when the next valid serial command is received or when the main blinking occurs (whichever happens first).
When the Maestro is reset in some other way than being initially powered up, the red and/or yellow LEDs blink four times to indicate the reset condition:
- Yellow off, red blinking: A brownout reset. This occurs when the Maestro’s 5 V line drops below about 3.0 V, usually due to low batteries or an inadequate power supply.
- Yellow blinking, red off: The Maestro was reset by a low voltage on its RST line.
- Yellow and red blinking together: A firmware crash resulted in a “watchdog” reset. This also occurs immediately following a firmware upgrade, as a normal part of the upgrade process.
- Yellow blinking, red steady: A firmware error resulted in a soft reset. This should never occur during normal usage.