MAP sensor "adapter"
Posted: Sun Dec 29, 2013 3:16 am
Some may be aware, others may not, so some "history"....
I've been toying with an idea initially intended to allow alternate MAP sensors to be used with the ECU my motorcycle uses. Replacement sensors for these bikes are mostly non-existent, or cost far too much than a used sensor should, as they were only made for two years- 1982 and 1983. This lead me to the idea of 'translating' one MAP sensor's output in order to emulate another.
The bike is an '82 Honda CX500TC and its EFI system was the first step taken in Honda's PGM-FI system. It runs alpha/N within a certain throttle position range then switches to speed/density at another range. The 500T used an external ignition controller in 82, and it's successor, the 650T integrated ignition within the ECU but was otherwise mostly the same. A group of MAP sensors, 4 in the 500T and 3 in the 650T (ignition change reduced the number of MAP sensors required), measured barometric pressure and manifold pressure both less than and above 1 bar, and adjusted fuel accordingly; the 4th sensor on the 500T adjusted ignition advance.
What I have is one op-amp to scaling the 5v output from the ECU and MPX4250AP MAP sensor to 2v5 to be sampled by a 12 bit ADC, a 12 bit dual DAC to output two voltages, and another op-amp sampling the DAC outputs for control / accuracy. My ECU's required accuracy is +/-0.2V and it seems I can achieve better than +/-0.02v accuracy with the DAC being used. Also, there is a provision for one of the 'cheap' BMP085 modules to be used as a barometric pressure sensor and temperature compensation (when the firmware is written and supports it). The MCU, in my case is a $12 MSP-EXP430F5529LP running at 25MHz, and the dev board itself will provide USB connectivity for programming via USB device and monitoring via USB back-channel / serial port.
I would appreciate comments, suggestions, criticisms and even assistance in coding.
Thank you.
I've been toying with an idea initially intended to allow alternate MAP sensors to be used with the ECU my motorcycle uses. Replacement sensors for these bikes are mostly non-existent, or cost far too much than a used sensor should, as they were only made for two years- 1982 and 1983. This lead me to the idea of 'translating' one MAP sensor's output in order to emulate another.
The bike is an '82 Honda CX500TC and its EFI system was the first step taken in Honda's PGM-FI system. It runs alpha/N within a certain throttle position range then switches to speed/density at another range. The 500T used an external ignition controller in 82, and it's successor, the 650T integrated ignition within the ECU but was otherwise mostly the same. A group of MAP sensors, 4 in the 500T and 3 in the 650T (ignition change reduced the number of MAP sensors required), measured barometric pressure and manifold pressure both less than and above 1 bar, and adjusted fuel accordingly; the 4th sensor on the 500T adjusted ignition advance.
What I have is one op-amp to scaling the 5v output from the ECU and MPX4250AP MAP sensor to 2v5 to be sampled by a 12 bit ADC, a 12 bit dual DAC to output two voltages, and another op-amp sampling the DAC outputs for control / accuracy. My ECU's required accuracy is +/-0.2V and it seems I can achieve better than +/-0.02v accuracy with the DAC being used. Also, there is a provision for one of the 'cheap' BMP085 modules to be used as a barometric pressure sensor and temperature compensation (when the firmware is written and supports it). The MCU, in my case is a $12 MSP-EXP430F5529LP running at 25MHz, and the dev board itself will provide USB connectivity for programming via USB device and monitoring via USB back-channel / serial port.
I would appreciate comments, suggestions, criticisms and even assistance in coding.
Thank you.