3.4. LED feedback

The Tic Stepper Motor Controller has three LEDs to indicate its status.

The green LED indicates the USB status of the device. When you connect the Tic to a computer via a USB cable, the green LED will start blinking slowly. The blinking continues until the Tic gets a particular message from the computer that indicates that the Tic is recognized. After the Tic gets that message, the green LED will be on, but it will flicker briefly when there is USB activity. During suspend mode (i.e. when the Tic is only powered from USB and the computer has gone to sleep), the green LED will blink very briefly once per second.

The red LED indicates that an error is happening. The red LED is tied to the ERR pin. For more information about error handling, see Section 5.4.

The yellow LED indicates the status of the stepper motor and also gives some information about what errors are happening, if there are errors:

• If the stepper motor coils are energized (i.e. electrical current is flowing), then the yellow LED will be on solid most of the time.
  • If the motor is moving forward (i.e. the current velocity is positive), the yellow LED will fade in for 0.5 s and then stay on at full brightness for 0.5 s:
  • If the motor is moving in reverse, the yellow LED will fade out for 0.5  and then turn on at full brightness for 0.5 s:
  • If the motor is energized, but not moving, and there are no errors, the yellow LED will turn on at full brightness:
  • If the motor is energized and there is any error happening other than a safe start violation, the yellow LED will stay on most of the time, but will periodically blink off twice:
  • If the motor is energized and a safe start violation is the only error happening, then the yellow LED will stay on most of the time, but will periodically blink off once:
• If the stepper motor coils are de-energized, then the yellow LED will be off most of the time.
  • If there is a motor driver error (i.e. from an over-current or over-temperature condition), the yellow LED will blink 8 times per second: This blinking will look very similar to the abnormal startup blinking described below, so if you see it, then it is best to look at the Tic’s status using the Tic Control Center software to figure out what is happening.
  • If there is no motor power supplied to VIN, or the voltage is too low, the yellow LED will blink slowly once per second (on for 0.5 s, off for 0.5 s):
  • Otherwise, if the motor has been intentionally de-energized by receiving the De-energize command over USB, serial, or I²C, then the yellow LED will be off most of the time, but periodically blink three times:
  • Otherwise, if the motor is de-energized and any error is happening other than a safe start violation, then the yellow LED will be off most of the time, but periodically blink two times:
  • If the motor is de-energized and the only error is a safe start violation, then the yellow LED will be off most of the time, but periodically blink once:

Note that the Tic does not read any feedback from the motor so it cannot tell if the stepper motor is moving, or if it is even connected. The LED blinking patterns above are based on the signals that the Tic is sending to the on-board stepper motor driver.

To ensure that the Tic shows a complete blinking pattern instead of switching quickly between two or more patterns, the yellow LED blinking pattern is only updated after it has completed. So if you make a change to your system, you might have to wait for one or two seconds to see the LEDs respond.

The information expressed by the Tic’s LEDs can also be seen by connecting the Tic to a computer via USB, running the Tic Control Center, and looking in the Status tab.

Startup blinking

When the Tic starts running, it tries to detect if it was reset by some special condition. If the Tic experiences a brown-out reset, watchdog timer reset, software reset, stack overflow, or stack underflow, the Tic will blink its yellow LED eight times over a one second period while the red LED is on at startup. While it is doing this blinking, the Tic will not accept any commands, read any inputs, or energize the stepper motor. You can see the cause of the last reset in the Tic Control Center software’s “Last reset” field. This startup blinking was added in firmware version 1.02.

Bootloader mode

In bootloader mode, which is used for updating the firmware of the Tic and should only rarely be needed, the LEDs behave differently. The green LED still indicates the USB status, but it is different: after the bootloader gets a particular message from the computer that indicates that the bootloader is recognized, the green LED will start doing a double blinking pattern every 1.4 seconds. The yellow LED will usually be on solid, but it will blink quickly whenever a USB command is received. The red LED will be on if and only if there is no firmware currently loaded on the device.