Using the DC power jack

With the standard motor.

Version 1.2 of the dispenser has two ports which can be used for power. The first one is the USB located at the back of the unit and the second is a standard 5.5mm outside diameter, with 2.1mm center positive pin, it’s the most common type (note: do not attempt to power the dispenser with both simultaneously!)

By default the DC jack is connected in parallel to the USB port. This means you should only use 5V power adapters, rated 1A or more. Remember, before using this port double check with your multimeter for voltage and polarity, don’t trust the label!

 

 

With bigger motors.

The machine has been optimized to work with the default stepper motor but if you want you can also connect much larger ones, the motor driver is capable of up to 2A of current.

To reach these levels you’ll need a power supply with a voltage output of 12V to 20V

– Open the dispenser and locate these solder jumpers J1 and J2 at the bottom:

jumpers
(note: this is a test board, DC jack is normally pre-installed)

– Desolder J1 and short J2, make sure there’s no solder left at all in J1.

-Add a standard 7805 regulator on the top left side, according to the silk screen on the board.

Note: From version 1.25 (september ’16 onwards) the regulator can now be soldered on the PCB or secured with a 4-40 or M3 screw.

 

Here’s a simplified diagram of how it works:

 

input_block

 

As mentioned before, by default the DC connector is in parallel to the USB port, therefore you can only use 5V power supplies. But when you short J2 and open J1 the stepper driver is powered directly, while the boost converter will be disabled by the microcontroller, which in turn is now powered by the 7805 regulator that you need to add.

Note: You can’t use the USB port once you’ve installed a regulator, you would have to remove it again If you want to go back to using a USB cable.

 

For the motor cables you can use a standard 4 pin 0.1” female header, or use the intended locking polarized version, Molex part number: 50579404

Molex-50-57-9404

Now that you have a new motor connected and a higher voltage supply, the only thing left to do is  change the current limit of the stepper driver. As explained in changing torque and power consumption you need to measure the “Vref” test point while adjusting the trimmer very slowly. Use this formula: Motor current=Vrefx2

Set the current according to your motor specifications and you’re done!

Remember, you can use a higher voltage supply than the motor rating, so for example with a 4V motor you can use a 12V supply no problem. As long as the current limit is set correctly the motor won’t be damaged.

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