Group work

Introduction to our work

For the group work, we made a very BIG 'useless box' in Fablab Shanghai. And during the tow weeks development, I am in charge of Embedded programming, and also helped with my friends in structure design.
If you search on google, you can find a lot of useless boxes. they are very lovely and intresting. Then we deside to make our own box. And to make it more interesting we will make 3 switches on one box.
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When someone moves the switch, the hand will come out and return the switch back to where it was. This series of action does not lead to any real change, so this is why it is so useless. However, ultimate useless box is even a greater idea, because it has three switches in a row. When someone chooses to move any of the three switches, the secret hand will move to the right position and return the switch. Although useless box has no real value, it requires a lot of technical work to complete this project. Let me tell you in details how to create such a useless thing.

Coding

For programming, there are one stepper motor and one DC motor to be controlled. The function of the stepper is to mover the 'hand' to hit different switches. And the DC motor will actrually press the switches. avatar
About the workflow of programming is not so hard. MCU keeps sense the states of 3 switches, whenever one switches triggered, the hand will move to the corresponding position to that one. Then drive DC motor to 'Push'.
There are one problem that I met. That is the stepper motor cannot 'remember' the start point every time when system powered up, where it can be random position depends on last time operation. In order to solve this problem, I added an overtravel-limit switch.
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When the system powered up, the 'hand' will keep moving to overtravel-limit switch until it was touched. In this way, every time we can have the same start point to ensure the accurancy of the system.
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Files download

Code