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  • rover109 commented on TechKiwiGadgets's instructable LED 3D Printer Bed Leveling Tool7 months ago
    LED 3D Printer Bed Leveling Tool

    I thought a bit before bringng it up because I didn't want to lsound like one of those instant web experts who tell cleverer people where they went wrong. YouTube comments are full of them. But I'm glad to learn that the point simply escaped your attention. Good that you still have the test jig set up and that you have by no means finished developing this concept.

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  • rover109 commented on TechKiwiGadgets's instructable LED 3D Printer Bed Leveling Tool7 months ago
    LED 3D Printer Bed Leveling Tool

    Unless I've missed seeing it you don't give much detail of the layout of the LM339 board. You do give a hint with a picture of the copper side of the 7x21 hole strip board with tracks cut and you must correctly assume that anyone skilled enough to tackle this project will be able to figure it out.What did you do about the three unused comparators on the LM339? It's a question that often arises regarding unused op-amps and comparators because of the possibility of stray coupling between output and inputs inducing oscillation with attendant high current drain and HF noise that can be induced into the active unit(s) on the chip. The answers to the possible problem range all the way from biasing all unused inputs to a known state through to grounding all unused inputs and sometimes groundin...

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    Unless I've missed seeing it you don't give much detail of the layout of the LM339 board. You do give a hint with a picture of the copper side of the 7x21 hole strip board with tracks cut and you must correctly assume that anyone skilled enough to tackle this project will be able to figure it out.What did you do about the three unused comparators on the LM339? It's a question that often arises regarding unused op-amps and comparators because of the possibility of stray coupling between output and inputs inducing oscillation with attendant high current drain and HF noise that can be induced into the active unit(s) on the chip. The answers to the possible problem range all the way from biasing all unused inputs to a known state through to grounding all unused inputs and sometimes grounding the unused outputs as well. From my limited understanding the scheme adopted depends on the design parameters of the particular type of chip.You report that your design is satisfactorily stable and I'm just wondering what you did about the unused pins or whether its not really a problem.in this design.The National Semiconductor LM339 datasheet suggests "ALL pins of any unused comparators should be tied to the negative supply."OnSemi suggests "It is good design practice to ground all unused INPUT pins." (capitalization is mine)I believe it is okay to tie the LM339 outputs to ground because it is an open collector design.I will probably tie all unused pins to ground. No trouble to run a shorting jumper from pin to pin. I'm still waiting for my LED array to arrive in the mail so I will probably breadboard the LM339 circuit as you suggest while I'm waiting and look for any spurious oscillations with a 'scope and then verify that a grounding scheme does no harm. Then I'll build it onto my bit of stripboard.You could either disregard the issue if you are satisfied that floating pins do no harm or you could add a note about it to the Instructable text.

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  • rover109 commented on TechKiwiGadgets's instructable LED 3D Printer Bed Leveling Tool7 months ago
    LED 3D Printer Bed Leveling Tool

    Had not heard of the ws2812 LED array before but I have now! Your project looks intriguing and for the price of the LED array it looks well worth trying. Everything else is in my junk box and my own Ender 3 is looking for a print job to perform. Will post again to say how my build went.

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