Quantity   Component name
1 × Magnetic Stir Bar / "Rührfisch" https://www.amazon.de/gp/product/B01AW7MR7Y/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1 This is the Stir Bar.
1 × Magnets / Scheibenmagnet Ø 16,8 mm https://www.supermagnete.de/wasserdichte-magnete-neodym/scheibenmagnet-durchmesser-16.8mm-hoe They don't need to be watertight, but these are the ones I had at Hand.
1 × Standardmotor This one is from the Drawer... maybe there are better Motors.
1 × LM317 Power Management ICs / Linear Voltage Regulators and LDO
1 × USB or other power connector
1 × Potentiometer 10k
1 × Resistor 3k4 Depending on your Motor and Supply Voltage (I Used this with 5V Power Input)
1 × Switch Simple Switch for switching on and off.
1 × Cables (<2m)
1 × Depending on your taste... a bit Of Stripboard You might also be able to create it with flying wires.