Over-engineered Decade Box

MCU controlled resistor decade box

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I've seen recently on EEVBlog ( a resistor decade. I knew in the very first moment, I want one, and also I know that I hate that kind of rotary switches.
So, I want to created a decade box without them. In this one, I'll use MCU, relays, relay drivers, power supply, LED or LCD display, microswitches, and so.
It will be totally over-engineered, costly thing. And it will be fun designing and building it.
  • 1 × MSP430G2452 16bit MSP430 value line Microcontroller
  • 1 × MCP23017 16Bit I2C I/O Expander
  • 3 × MCP23008 (PCF8574) 8Bit I2C I/O Expander
  • 24 × Rayex LEG-5F PCB mount 5V Relay
  • 3 × ULN2803 8xDarlington Array

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jaromir.sukuba wrote 01/02/2016 at 23:46 point

Are you going to push this one further?

In autumn 2014 I spent few days in bed with flu. As I couldn't do anything else, I watched older episodes of EEVblog, especially one with decade box teardown. Immediately I thought about making resistor box - binary of course. I went as far as selecting appropriate 0,25% low tempco resistors from Mouser to set up the binary resistor chain. Later, sanity kicked in and I scrapped the project. 

Interesting enough, it was about the same time you started this project and resulted in similar topology.

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SUF wrote 01/03/2016 at 05:07 point


This is still in my plans, but I think, this will take a while. In the last few years, I had several project ideas, I started to work on plenty of it. Finally I realized, that my projects didn't go anywhere. So a few month ago I decided, to work on them one-by one. Trying to finish my half completed projects.
As this one is just an idea in my head (and collected parts), probably not the first one I'll finish. Now I'm working on my build siren, what is almost ready (few days left).

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jaromir.sukuba wrote 01/03/2016 at 12:42 point

Yes, understood. I have "a few" half-baked projects too - that's why I scrapped the resistor box, not mentioning the fact I don't need any resistor box :-)

Good luck finishing the projects, sometimes it is boring and annoying, but the result is worth all the work.

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Stefan-Xp wrote 07/23/2014 at 18:21 point
Non of the mentioned projects did feature a MCU?
I think it is a rather interessting quest ;-)
I did a 9-Value-PC-Controllable-Decade-Box on my day job a time ago, that was easy :-D
A seven decade resistor box has 70 switching points.
Would be interessting to see a nice overengineered Seven-Decade box with lots of relays or optocouplers ;-)

Best regards!

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SUF wrote 07/24/2014 at 04:43 point
seven decade is great, but why 70 switching points? If we are talking about MCU controlled one it can be binary and the UI decimal. In theory it can be achieved with 24 switching points (2^24). :-)
My intention was to do it in 2^10 increments and not using the values above 1000. With 24 relays I can achieve a scale from 1R to 16M

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SUF wrote 07/23/2014 at 11:56 point
Thank you for your reply. Corrected the typo.
I was not aware of the projects you mentioned. Seeing the second one I deeply reconsider to even start to working on this project.
Thank you,

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davedarko wrote 07/23/2014 at 12:05 point
Oh crap, that was not my attention :( I thought they would be helpful but not killing a project :(

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SUF wrote 07/23/2014 at 12:13 point
Never mind! I've plenty ideas in my head, just not enough time to work on them. I'll post other projects instead of this. :-)

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