Only for External Encoders!
If you are using Feedback 360° servos, go to Feedback 360° Servo Test instead.

It’s time to test your robot’s external encoder signal connections to make sure they are in proper working order.  This test is essential before trying any navigation programs. Each external encoder sensor can see the spokes in the wheel right next to it.  If the external encoder is working correctly,  a built-in LED on the Activity Board will turn on each time it detects a spoke, and turn off when the hole between the spokes passes by.  

• Log into your BlocklyProp account, and run the BlocklyProp Client on your computer.
• Create a new project, named Test Encoders.
• Build the project shown below.

• Turn the robot’s power switch to position 2.
• Click the Load and run (save to EEPROM) button.
• With your hand, gently twist the ActivityBot’s left wheel, which should make the P26 LED turn on and off as you rotate the wheel.
• Repeat for the right wheel.  Turning the right wheel should make the P27 LED turn on and off.

If It Doesn’t Work…

Here are some symptoms and causes:

P26 light stays off while turning the left wheel.

• The left encoder cable may be plugged into the P14 servo port backward.
• The 20 k-ohm resistor (red-black-orange) may not be making contact at either the P14 or 3.3 V socket.
• The left encoder may be mounted with the sensor facing the chassis instead of facing the wheel spokes.
• The shunt jumper may be missing from the power selector pins next to the P14 & P15 servo ports.

P27 light stays off while turning the right wheel.

• The right encoder cable may be plugged into the P15 servo port backward.
• The 20 k-ohm resistor (red-black-orange) may not be making contact at either the P15 or 3.3 V socket.
• The right encoder may be mounted with the sensor facing the chassis instead of facing the wheel spokes.
• The shunt jumper may be missing from the power selector pins next to the P14 & P15 servo ports.

P27 light instead of P26 light blinks while turning the left wheel (or vice versa).

• The encoder cables are swapped! Switch the encoder cables plugged into P14 and P15.

P26 or P27 light stays on while turning a wheel.

• Resistor connecting P14 or P15 socket to 3.3 V socket is too small. It should be 20 k-ohm (red-black-orange-gold). This resistor came in the bag with the encoder parts, not with the rest of the resistors in the kit.

The encoder’s light stays on all of the time, or most of the time but occasionally flickers off.

• The encoder might be mounted so that the sensor faces inward toward the chassis instead of outward toward the wheel spokes. Un-mount and swap them, so they face outward.
• You may need to adjust the bracket position. For kits made before October 2013, the encoder bracket may be mounted just out of alignment, so it sees the rim below the spokes instead of the spaces in between the spokes. If there is a gap between the bottom of the servo case and the lower edge of the chassis mounting hole, this is likely the problem.  It is easily corrected by loosening the servo screws slightly, then retightening while at the same time pulling the encoder bracket and servo away from each other.

Both P26 and P27 stay on at all times during the test

• The jumper for P14 & P15 may be faulty, or not making the proper connection. Make sure it is pressed all the way on to the pins, and that it is not cracked, loose, or otherwise damaged.

WARNING: If any of your jumpers are damaged, contact technical support (support@parallax.com) and do not apply power to the affected headers!

If Both Encoders Work

Congratulations! It is time to calibrate your ActivityBot.

• Follow the links below to continue.