Knock Block

Step 6 Stock your block

Here you can see the battery resting on one side of the acrylic bracket, the Arduino on the other side with the transistor for the solenoid sticking in it at an angle, and the solenoid in the middle - screwed into a block of MDF to hold it steady - and the piezo sensor taped to the MDF block. Some calibration was necessary to make sure the solenoid hit the tongue of the lid well, and we put a piece of felt under the solenoid hammer to keep it at the right height.