Design cleanup

Thread Starter

metermannd

Joined Oct 25, 2020
83
So, I'm still playing around a bit with electronics design, trying to sharpen my skills since this whole mess outside keeps me from following my other hobbies...

I'm looking at the design of one board I have here, and which was set up so it could be populated quite a few different ways (not counting jumper wire / trace-cut mods) depending on usage. I'm mulling laying out a purpose-built version to go with the other two boards I've done so far.

I have four questions:

1: Note the three comparator sections with outputs marked AI2, AI3, AI4. Normally, the input for each is at the junction of the 330K and 5.6K resistors at the (-) input, but since the inputs are not connected in this arrangement, I could just eliminate the entire section, except the 3.3K pull-up at the output, right?

2: Note the one comparator section marked with input "Init" and output "Init_En". All this section does is drive the Init_En output low as needed, and was executed by rearrangement of an input stage to form an output (that is why one resistor is currently designated as if it was a cap. Will correct it once I further redraw this schematic). My question: If the comparator is merely there to provide a logic high / low, what other parts should be present for 'best practice'?

3: Note the ULN2003 IC. On a fully-outfitted board, this IC serves as the driver for up to five relays and two digital outputs. In this configuration, it drives only one relay. What can I use to eliminate this IC? Would something like a 2N6427 or 2N3904 suffice?

4: T4 is a potential stumbling block. It is a small CT, used as part of a circuit to pick off the carrier signal from the incoming power. Are all such CTs purpose-built or are there actually 'generic' CTs out there? I may have an alternate circuit I could swap in, using a capacitive divider instead.

Appreciate the feedback and answers I've received thus far.

board-D.png
 

Thread Starter

metermannd

Joined Oct 25, 2020
83
Moved into the 'moot' column.

(Another forum I frequented often spoke of the 'power of the post', where someone would be stuck, posting where they were at with a given process, only to get the needed inspiration AFTER the post. That just happened to be the case here.)

Item 1: Reduced the idle sections to the pull-ups, consolidated with R95 into a network pull-up (4x 3.3K).
Item 2: Left as-is but swapped comparator to 2-up LM2904, properly (hopefully) tied off unused section
Item 3: Consulted my library of related schematics, found circuit snippet I needed and incorporated.
Item 4: Again, consulted my library of related schematics, swapped T4 / C45 / R63 with cap / inductor / resistor combo.
 
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