• josevar700's D12 ADC Schematics:
  

Bottom line is, you can put any 0 to 5V signal on a USDM P30 D12 pin, and log it by reading RAM location 0067h. That RAM location contains a byte that gives you the input voltage in 0.02V increments from 0V at 00h to 5V at 0FFh. Keep in mind that there is about a 1% drop in voltage from pin D12 to Pin 57 on the 66207 chip (AI3 analog input port), although that is probably negligent. If you want to get really accurate, you can also read RAM location 0066h to get the least significant two bits of the 10 bit A/D converter data, but that seems like overkill for EGT logging. Note that in the USDM P30, the AI5 analog input pin is grounded.

Bottom line is, you can put any 0 to 5V signal on a USDM P30 D12 pin, and log it by reading RAM location 0067h. That RAM location contains a byte that gives you the input voltage in 0.02V increments from 0V at 00h to 5V at 0FFh. Keep in mind that there is about a 1% drop in voltage from pin D12 to Pin 57 on the 66207 chip (AI3 analog input port), although that is probably negligent. If you want to get really accurate, you can also read RAM location 0066h to get the least significant two bits of the 10 bit A/D converter data, but that seems like overkill for EGT logging.

C42 is unstuffed in a stock USDM ECU, so it is a really good idea to put a 1uF 35V tantalum cap in C42. This provides a nice filter to smooth the ADC analog input. Make sure you install the cap with the plus side the same as all of the other caps in that row, away from the 66207.

Note that in the USDM P30, the AI5 analog input pin is grounded.

Another application for this input could be for a kill switch input. A clever person could use this feature to make a plugin for the ECU software to read a kill switch with a pullup resistor to disable the ECU if the switch is set to disable the ECU or enable the ECU if the switch is the other way. Of course, that would make it so you couldn't log EGTs or anything else, but not everyone is into logging. There are probably a lot of other applications that D12 could be used for. We just need clever programmers.

-- markolson - 20 Nov 2005

You could use this input as a 0-5V input for a wideband O2 data, leaving the stock O2 sensor input for the narrow band O2 data. Another application for this input could be for a kill switch input. A clever person could use this feature to make a plugin for the ECU software to read a kill switch with a pullup resistor to disable the ECU if the switch is set to disable the ECU or enable the ECU if the switch is the other way. Of course, that would make it so you couldn't log EGTs or anything else, but not everyone is into logging. There are probably a lot of other applications that D12 could be used for. We just need clever programmers.

-- markolson - 20 Nov 2005, Edited -- markolson - 02 Jan 2006

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