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

This project received 5 bids from talented freelancers with an average bid price of $164 USD.

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IMPORTANT: I require you to have experience using magnetic stirrers AND knowing how they work.

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 (buttons) should be of the mount type (on the box).

I imagined that there would be a main adapter with fixed 12V Voltage with its corresponding socket, a reusable fuse to protect the rest of the components, then a master switch to turn the device on, a potentiometer with a switch and a light to control the speed of the fan with glued magnets, another potentiometer with a switch and a light to control a thermoelectric heater - both would be independent.


• All the electronics would be soldered and glued inside a plastic box, except the heater 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 3L of liquid and not heat it above 150°C.

• a board should be avoided unless absolutely necessary and it should be narrow so as to fit to the side of the fan, not below

• 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 2 different models of devices:

#1: using a fan with glued magnets

#2: using a fan with glued magnets + heater

• PIC microcontroller and any kind of software must be avoided

• Peltier element seems the most adapted to this project

• the box will be thin and rectangular

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 must be this and depends on that)

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

- as an optional extra task and if you are knowledgeable 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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