This in-progress project is an upgrade of the previous twisted-pair winding machine designed to wind cable for use in Oscilloscope isolation transformers.
The new machine uses two stepper motors to achieve infinitely variable options for wire pitch, a significant improvement of the limited eight gear ratios of the previous design.
The use of steppers also means that pitch can be varied during operation, which allows for an additional feature of creating ‘hard twists’ at the wire ends, which significantly improve the ease of winding the transformers by preventing unravelling.
This is accomplished by altering the step ratios such that both steppers turn at the same speeds, causing the wire to be twisted without advancing. During this operation, a motor driven clamp pinches the wire a short distance from the twisting armature, fixing the length of the hard twist.
The tensioner has also been redesigned from the relatively primitive friction washers, to a closed-loop feed motor allowing a constant and balanced tension to be maintained.
The system is controlled by an Arduino Nano, with two DRV8825 stepper drivers, and an L293D H-Bridge IC to provide motor control.
Power for the DC motors is provided by a 5V fixed-output buck converter, separate from the linearly-regulated 5V logic supply to avoid the risk of electrical interference.
A 5110 LCD module is used as the user interface. These relatively inexpensive modules were originally used in Nokia 5110 mobile phones, and have become a common staple for hobbyist electronics.
The UI features a Settings menu, where run-parameters can be edited and stored into non-volatile EEPROM, and two modes: Manual Advance, and Run. The latter allows wire to be driven through the twisting armature automatically, something which on the original machine was a relatively difficult task due to the need to manually rotate the armature.
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