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EEVblog 1472 - Resistor Cube Problem SOLVED

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EEVblog:

--- Quote from: erosenberg on May 05, 2022, 10:54:39 pm ---Nice method of simplification!
What is the drawing software being used here? Looks like it is helpful for teaching and presentations.

--- End quote ---

Drawboard PDF, aussie company, originally designed for marking up architecture drawing. i.e. make changes and save as a PDF.

armandine2:

--- Quote from: hulk69 on May 05, 2022, 10:20:58 am ---This exercise got me looking for the Weathstone bridge, but the more I look at it the more I cannot find any use for it nowdays.

Any op-amp circuit like a non inverter would do a better job...

As I see it the Weathstone bridge is just a good exercise for beginners to learn the Kirchhoff law

--- End quote ---

still in use? definitely still taught

twospoons:

--- Quote from: free_electron on May 05, 2022, 01:58:52 pm ---
now do it for a set of resistors that is 1, 1.1 1.2 1.3 1.4 and so on in different permutations. and try also opposite corners fo the cube...


--- End quote ---

The resistance between opposite corners of the cube (A and G in the video) is even easier to solve. By inspection you can see that points B,D,E must be the same voltage, and points C,F and H must be the same voltage ( the joys of symmetry). So the three resistors from point A may be considered to be in parallel, and the three resistors from point G may be considered to be in parallel. The remaining 6 resistors must also have identical voltage drops since they all connect from the B,D,E point group to the C,F,H point group so they may be considered in parallel too.

Therefore RAG = R/3+R/6+R/3 = 5/6 R

Vtile:

--- Quote from: hulk69 on May 05, 2022, 10:20:58 am ---This exercise got me looking for the Weathstone bridge, but the more I look at it the more I cannot find any use for it nowdays.

Any op-amp circuit like a non inverter would do a better job...

As I see it the Weathstone bridge is just a good exercise for beginners to learn the Kirchhoff law

--- End quote ---
Bridges are important still today for high precision instrumentation.

The beayty of bridge circuit is that is provides integrated high stability voltage reference (assuming one unknown) and passive (pseudo) amplifier.

It also still can be made to be totally passive so no interference from electronic amplifier and it is also considered instrically safe for EX-spaces ie. with Pt100.

It definedly is not a mainsteam, but it have never been mainstream.

It is one of those rare circuits which can be used to push the limit further than the used components by iteration.

Ps. The common "equation" floating around is oversimplification when effect of sensing device is assumed to be zero ie. infitely high resistance over the bridge halfs and equilibrium state.

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