While there are many analog inputs (that can also be used for GenBoard/UnderDevelopment/DigitalInputs of coruse), the pinout has not been standardized yet.
proposal for extra ADC input channels
EC18 beware that these inputs are unbuffered and unfiltered, care must be taken to avoid damage to the MCP3208.
- EC18pin12 direct to MCP3208pin8 (ch7) (standard for secondary_trigger=HALL)
- EC18pin6 direct to MCP3208pin7 (ch6) (standard for internal MAP sensor)
- EC18pin16 direct to MCP3208pin6 (ch5)
DSUB9 male on endplate.
Unfortunately both genders are used: DSUB9 female used for RS232 and DSUB9 male used for LCD. When an ECM has DSUB9 male for both LCD and extra inputs, care is needed at hookup.
- DSUB9pin1 GND
- DSUB9pin2 OC3C Voltout - negative
- DSUB9pin3 MCP3208pin3 (ch2) - negative
- DSUB9pin4 MCP3208pin2 (ch1) - negative
- DSUB9pin5 MCP3208pin1 (ch0) - negative
- DSUB9pin6 OC3C Voltout - positive
- DSUB9pin7 MCP3208pin3 (ch2) + positive
- DSUB9pin8 MCP3208pin2 (ch1) + positive
- DSUB9pin9 MCP3208pin1 (ch0) + positive
The internal HW
The midopa provides 3 nice features:
- differential inputs
Values for different amplification:
- buffering (*0.99, measured in one example case: 945mV output / 951mV input). Input range is appr 5V.
- x17.5: input range is appr 285mV (this is the minimum recommended when used for extra K-type thermocouple EGT input, if the onboard 2 is not enough)
MCP3208 input load
When using v3.x in an industrial application ( stimulator and tester for a manufactured circuit), we applied external 10k and BAV99 diode protection (quite standard values) to protect the mcp3208 from voltages higher than 5V (or lower than 0). This is not needed when it can be guaranteed by other means that input will only get 0..5V: not an issue when used for pushbutton / switch, we use without extra protection than.
We found that 10nF caps are needed on the mcp3208 inputs for exact measurement when 10 kOhm protection is used: without cap, the internal sampling cap loads the input (likely towards GND) too heavily (impossible to measure with DVM as sampling takes _very_ short time !). With 2MHz SPI clock 4V input could only charge the sampling to 3.3V (this we measured; 500ns time constant is appr 50pF * 10kOhm; not sure if the mcp3208 datasheet specifies so high sampling cap, but PIC microcontrolles taught us in the the past that with microchip we must be careful with datasheet anyway). This could be handled in software with lower SPI clock, but the cap is a good idea in this case (makes the protection circuit 3 components, not 2).