Electronics > Beginners
Not measuring 0v/gnd through ground resistor
rstofer:
You can turn the switch around (metaphorically) and for each specific LED pattern, you wire the input to the proper pin. They won't be in the order they are now but so what? When both LEDs are lit, you are apparently selecting input 3. Fine, whatever signal should be active as input 3 should be connected to the chip input IN0.
SW LEDs
Closed Closed ON ON Looks like selection 3 so connect 3rd signal to IN0
Closed Open ON OFF Looks like selection 2 so connect 2d signal to IN1
Open Closed OFF ON Looks like selection 1 so connect 1st signal to IN2
Open Open OFF OFF Looks like selection 0 so connect 0th signal to IN3
bitman:
I did a breadboard using the original design but using resistors to connect ground and high directly to the chip as indicated here. This works - my original design did not use resistors between ground and the entry point, so I guess that's the problem and I'll have to revisit the calculations shown here to get the proper values. This is my guestimate that looks like it works when isolated:
And the breadboard if anyone is interested looks like this - this behaves as expected. When the two selectors are low, the "LowBit" switch is connected to out. When the first switch is high, the "HiBit" works (yeah, bad name). And when the second dip switch is high and the first is low I get a constant high. This is for proof of concept only - there are 3 input signals in the real circuit - it's not using push switches.
So I'm not getting the "default to high" - if I did that, I would have S2 high and give me the wrong result (or I would of course have to use different output pins). I've always pulled unused pins to low and it's never caused an issue - but reading between the lines here, it seems to be more efficient to tie them high. I'll have to experiment some more here to understand it more.
But it looks like that when I need signals to toggle, using a resistor via gnd or +5v results in more reliable results for me.
So yes - still a confused newbie but on the right track (I think). Thanks again for the posts. While this may be basic for some of us - it is really helpful to me.
bitman:
--- Quote from: rstofer on October 27, 2019, 09:00:34 pm ---You can turn the switch around (metaphorically) and for each specific LED pattern, you wire the input to the proper pin. They won't be in the order they are now but so what? When both LEDs are lit, you are apparently selecting input 3. Fine, whatever signal should be active as input 3 should be connected to the chip input IN0.
--- End quote ---
That's how I implemented going from the original "gnd" when closed to "+5v" when closed. I can move things like led positions easily - that's not the challenge. The problem I had was that the switch position didn't matter. I kept measuring either +5v or gnd regardless of switch position. Now that I have the resisters between +5v and the switch, and the resister array between the switch and ground. While I still need to get the exact reason for this, it solves the problem.
But you're right - I could use different output lines - I would just have to redesign the PCB and get new ones made. Adding a resistor or two is something I can do without getting a complete new PCB.
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