Now that I'm out of the pickle I was in regarding the tank circuit, I noticed one other thing that I may be able to do with this board's design, and want to see if my thoughts are in the right place.
There are two supply voltages coming into the board (5V and one of the two 12V supplies), and it occurred to me that there are only two nodes on the 12V bus on this board. It appears that I may be able to make a couple slight changes to the circuit that would allow me to eliminate the 12V bus from this board, simplifying the overall setup.
I've attached the schematic of this panel and added dashed lines around the sections in question. (Existing / Proposed groups 1 and 2)
First, there is a 2.5V supply derived on-board for use with the comparators. Right now, that 2.5V supply is derived by way of a dropping resistor and zener diode. My question is, isn't a 'bare' zener diode like this liable to generate noise?
I'm seriously considering taking that out and replacing it with a pair of 10K resistors acting as a voltage divider off the 5V bus instead. I want to make sure I'm not missing out on some benefit of using a zener versus a simple voltage divider (I have a schematic of a related board that was designed a few years after this one and it has the 2.5V derived by voltage divider).
The second question has to do with a different voltage divider... again, what would the benefit be in tapping the 12V supply for this purpose?
I did the math and it appears that I can get approximately the same voltage and current with the indicated substitute resistor, fed from the 5V bus. Could it be that particular resistor value was not available in a 1/4W axial resistor package back in the early '80s and they took this route?
If my guesses are right, this would enable me to remove one of the two 12V supplies from the power board.
There are two supply voltages coming into the board (5V and one of the two 12V supplies), and it occurred to me that there are only two nodes on the 12V bus on this board. It appears that I may be able to make a couple slight changes to the circuit that would allow me to eliminate the 12V bus from this board, simplifying the overall setup.
I've attached the schematic of this panel and added dashed lines around the sections in question. (Existing / Proposed groups 1 and 2)
First, there is a 2.5V supply derived on-board for use with the comparators. Right now, that 2.5V supply is derived by way of a dropping resistor and zener diode. My question is, isn't a 'bare' zener diode like this liable to generate noise?
I'm seriously considering taking that out and replacing it with a pair of 10K resistors acting as a voltage divider off the 5V bus instead. I want to make sure I'm not missing out on some benefit of using a zener versus a simple voltage divider (I have a schematic of a related board that was designed a few years after this one and it has the 2.5V derived by voltage divider).
The second question has to do with a different voltage divider... again, what would the benefit be in tapping the 12V supply for this purpose?
I did the math and it appears that I can get approximately the same voltage and current with the indicated substitute resistor, fed from the 5V bus. Could it be that particular resistor value was not available in a 1/4W axial resistor package back in the early '80s and they took this route?
If my guesses are right, this would enable me to remove one of the two 12V supplies from the power board.
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