The assignment for this week, was to make an output device. So I made a motor controller board. Some time ago I saw in Thingiverse a solder paste dispenser, that used a motor to push the paste.

Solder paste dispenser

So I decided to design one for myself. the general board I designed has a regulator to make sure if the board is connected to proper powersupply it doesnt fry the attiny44 chip on it. I also used h bridge chips to make my own stepper controller, instead of using the ready made stepper controller we had at the lab.

Since I like to use design blocks, it was easy to make the board, as I could just drop in most of the elements. Like the buttons and the main chip.I originally tried to have a potentiometer on the board but I couldnt find the proper footprint for it, and the one I found was too big. But the real design problems came with the H bridges.

Usually I like to pull lines from under the components. But in this case when i read through the documentation for them, to see what giblets they needed to function, I realized I could not pull anything from under them. As they had a ground connection in the bottom for heat dissipation. This complicates the design somewhat.

Not only that, but since the motor is a 24v one, I needed a proper connection for external power to run without frying the chip. A simple regulator solved this but still the 24v line needed to be handled separately. So I used a millimeter wide trace for it, when I usually use a 0.4mm traces for signals.

When it came time to program the chip, the arduino tutorial for controlling H-bridges was invaluable. arduino stepper control As this shows one how to use both the H-bridges and how to use the potentiometer to set the speed. In general the documentation of the ATtiny44 chip it self was not really necessary as the arduino language is higher level language and handles the things one would need to consult from the documentation.

For the additional part of this week, the idea is to make use of a nema 14 motor I have, and have it drive the screw for the paste pen.

As the plunger for it is being printed in the middle of the print I place a m5 nut into it, so that when the motor rotates it pushes the plunger down the syringe forcing paste out.

The problem is, that on its own the board I desgined for motor control is not suitable for this use. So I designed a new board, it is still work in progress, as I finalize the design. Idea is that one board is screwed on to the 3d printed pieces for mounting the motor and the syringe, while the narrow piece has the buttons for controlling the motor and can be more freely placed. Since its location is just matter of cable length, but once the board is ready I will design a proper mount for it, to turn the syringe into something one can hold like a pen. it also has 3 bright LEDs that illuminate the area where one is about to place the paste.

the main board also has 2 potentiometers, that control the power of the motor and the duration. So that one can control how hard the motor is pushing the paste and when the button is pressed once, for how long the motor runs.