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Messages - MPWeir

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Mach3 under Vista / Re: New setup for USB board by BSMCEO4U-PP Bitsensor
« on: January 09, 2021, 07:57:53 PM »
Sorry, I meant the two enable lines to the 'HC541 chip.  The ULN2003 doesn't have any.
Which brings up another design error.  The HC541 input logic levels are really not compatible with 3.3V driving logic.  The HCT541 would have been the right choice, but the part on my board is clearly marked <abunchofcharacters>HC541, with a TI logo.  The step and direction signals are coming out, though, so that part is working.
Mike
Ref:  Bitsensor BSMCE04U USB board

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Mach3 under Vista / Re: New setup for USB board by BSMCEO4U-PP Bitsensor
« on: January 09, 2021, 03:09:31 PM »
I was troubled by the lack of any good interface documentation for this Bitsensor board, and so traced the schematic before starting to hook it up.  Wvancura was correct, but the attached .pdf file provides more internal details.  The schematic reference designators are arbitrary, and the schematic symbols are approximately correct for the functional behavior (for example, the two enable lines to the ULN2003N chip are actually active low, but I didn't want to figure out how to make the new object for an Eagle library).  All voltages and returns are correct, as are the circuits associated with input and output.
There is a serious design error, if I have correctly interpreted the abbreviated surface mount device markings.  A series diode in the 24V supply line prevents the catch diodes inside the ULN2003 from suppressing the inductive flyback when an external relay is turned off.  The relay current will decay instead through a sneak path via an input if it has a switch connected to ground.  It would be a good idea to provide your own external relay coil suppressor diodes, making sure to connect them properly (cathode to the positive terminal).
Mike

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