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Switching to two boards means that 30 thermistors will not be accounted for. We could accommodate this by utilizing two of the current ADG731 MUXs for a total of 64 inputs per board that would monitor 45 thermistor cells each. This means that MUX1 would monitor 23 cells while MUX2 would monitor 22 cells. The remaining inputs will be dedicated to at least three on-board thermistors to measure the balancing resistors. These would be placed at the ends and middle of the battery stack as a priority. The output of the MUXs can be connected to GPIO1 and GPIO6 of the LTC6813.
Alternatively, we could use an addressable format to control 4 16:1 MUXs simultaneously. This would also remove the requirement to invert the signal clock. Careful planning of the thermistor connections will be required to prevent mixing up readings. Four of this component can be used to achieve this layout which meets our specifications:
https://www.digikey.ca/en/products/detail/texas-instruments/CD74HCT4067QM96Q1/3789546
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The conversion times of commands, such as the ADCV and ADSTAT, from both datasheets were found to take similar amounts of time, with differences in the range of microseconds, so there are minimal latencies in comparison. No further firmware changes are required as the LTC6811 has cross compatibility with the LTC6813. The major changes to the firmware would be the addition of the Group E and F battery cell commands for reading and balancing and thermistors.
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Based off the following spreadsheet, the 12-cell layout will cost the overall AFE system approximately $234.51 while the 18-cell layout will cost $204.70, allowing us to save $29.81 on the entire system. If the 64:4 MUX layout is used, then the total costs excluding complementary components is $169.34. so savings can be at most $81.61. The cost breakdown does not include the connectors, though they are included in the spreadsheet, as final harnessing and the necessary connectors are undecided and can differ substantially in comparison to the current revision.
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