Magnetic stirrer - draw schematics, explain how to choose components, suggest possible parts

This project received 2 bids from talented freelancers with an average bid price of $220 USD.

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IMPORTANT: I require you to have experience using magnetic stirrers AND electromagnets for this job.


I want to build cheap and simple to assemble magnetic stirrers.

Cheap means cheap parts (but good quality), simple to assemble means few parts, parts that cumulate features and parts that can be assembled manually.

Parts that the user needs to operate should be of the mount type (on the box).

I imagined that there would be a main adapter with fixed Voltage with its corresponding socket, a fuse to protect the rest of the components, then a switch to turn the device on, a light to indicate it’s working, a fan with glued magnets or electromagnets (depending on the cost and complexity) to spin the stir bar and a potentiometer to control its speed, and eventually a thermoelectric heater (heating plate) whose heat can also be controlled.

All the electronics would be soldered and glued inside an ABS box, except the hot plate which would be on top of it, eventually separated by a heat insulating material such as a tile.

The magnetic stirrer will not need to stir more than 2L of liquid and not heat it above 150°C.


• the switch + potentiometer should ideally be replaced by a potentiometer with integrated switch

• a board should be avoided unless absolutely necessary

• the circuit should be modular in a way that it does not need to be changed a lot when adding the hot plate or when replacing fan+magnet with e-magnets

I imagined 4 different models of devices:

#1: using a fan with glued magnets

#2: using electromagnets (depending on the cost and complexity)

#1: using a fan with glued magnets + hotplate

#2: using electromagnets + hotplate

Your job will be to

- draw the schematics (with English labels) for all the models of devices

- explain thoroughly the required specifications of each part based on the other parts (e.g. the potentiometer’s resistance depends on ...)

- find possible parts on an international store (such as conrad, radiospares or TME) and give the reference numbers

- as an optional extra task and if you are knowledgable about this you could give tips on assembling, materials and glues to use, air ventilation, thickness, etc

N.B. By applying for this job you agree not to disclose any document or information exchanged and to cede to me all rights over the created materials. Applications that ask too high price, ask for upfront or do not answer how the job would be done, will be rejected.

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