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Decided to start a project based discussion regarding the BP I posted http://forum.43oh.com/topic/4301-manifold-absolute-pressure-sensing/ so as to not clutter that up. For those that haven't visited that, here's a re-cap: MCU samples an MPX4250A absolute pressure sensor, takes the reading and looks up a value from a table, and sends that to a DAC for output. It's actually two DACs though so there are possibly two values to read and send. There's an SPI eeprom for storing the values and the DAC's are set over SPI as well. There will be software that interfaces to it, at least for the stand-alone version, that allows for altering the tables therefore making the unit able to read absolute pressure and output arbitrary voltages based on the readings. There will be two tables, more appropriately I guess I should call them arrays, with 256 entries. Not considering the accuracy of the MPX sensor, ADC or the DAC, considering 5 volts, that's a resolution of approximately 0.02 volts per cell / entry. Good enough, I think, for my purposes. Eagle board / schematics can be found at the link above.
I have to mention RobG and cubeberg have helped with this. THANKS!!!! What it is, is one pressure sensor affecting two, 16 bit DAC output channels. What it will do (hopefully ;-)) is read an (automotive) industry standard MAP (manifold absolute pressure) sensor- in this case an MPX4250A 20-250 kPa (kilo Pascal) / 2.9-36.3 PSI sensor (~100 kPa / 14.7 PSI is ambient pressure at sea level), and appear as up to two potentially different sensors. Possible uses could include: replacing obsolete MAP sensors with more readily available ones because of different output range / scaling; fooling a vehicle's engine control unit to allow for bigger injectors or turbocharging; splitting one MAP signal for two purposes; or affecting pressure controlled devices. The aforementioned MAP sensor will be connected to whatever vacuum / pressure source. The MCU will sample that and generate an output. But instead of doing a mathematical conversion, there will be look-up tables. This will permit non-linear adjustments to be made, allowing for compensation factors to be applied to the output, tuning. What I am uploading now, is a Booster Pack version of this, which should be usable with MSP430 and Stellaris/Tiva LaunchPads. Eventually, I want to have a complete stand-alone, with software to interface with it from a PC. I think we are close to that too; but still some details to work out. Hardware is: - MPX4250AP absolute pressure sensor- http://www.freescale.com/files/sensors/doc/data_sheet/MPX4250A.pdf - AD8644A quad op-amp- http://www.analog.com/static/imported-files/data_sheets/AD8614_8644.pdf - LTC2602IM dual-channel, 16 bit DAC- http://cds.linear.com/docs/en/datasheet/2602fa.pdf - 25AA512 eeprom- http://ww1.microchip.com/downloads/en/DeviceDoc/22021F.pdf - supporting resistors, capacitors, do dad's and whatnot's. Should probably mention I have added jumpers to disconnect V+ from either of the output sensor connections... the board is meant to be connected to the sensors and use their 5V+ to power the op-amp and provide external voltage reference for the ADC, but on my motorcycle one of the sensors has 12v and an internal voltage regulator. Therefore, I put the jumpers in so any sensor with inappropriate V+ could be kept out of the system. I've also put a jumper between the 5v from the sensors and the 3.3v LDO so that the LDO can be disabled if the LaunchPad is operating off USB. I do not have any presentable code to offer at the moment but am working on it; suggestions will be appreciated... and I'm working in Energia, which might have been evident with my post in the Energia forum: http://forum.43oh.com/topic/4292-multiple-slaves-on-spi/, so be kind. ;-) SingleBP.brdSingleBP.sch Comments and suggestions greatly appreciated. * Please ignore the name "SingleBP". I used that because the 500T version of my motorcycle uses 4 MAP sensors, and the 650T uses two. So "Single" means one unit needed for the 650T.
I finished up my first Energia project, a template library for the Bosch BMP085 temperature and pressure sensor. It uses I2C and supports temperature in Celsius and pressure in Pascal. https://github.com/astuder/BMP085-template-library-Energia I connected the GY-80 breakout commonly found on eBay, but it should also work with most other BMP085 breakouts, like the ones from Adafruit or Sparkfun. Note that I had to patch Energia to make 1-byte read work on MSP430G2553 with Rev1.5 LaunchPad. I also had to remove the LED2 jumper, probably due to too weak I2C pull-up. Update: Tested on LaunchPad 1.5 with MSP430G2553, StellarPad Rev A and Arduino R3. Energia requires patches 226 and 235 in twi.c for I2C to work properly on MSP430G2553 https://github.com/energia/Energia/pull/226/files https://github.com/energia/Energia/pull/235/files Updates: - Tested with Energia 0101E0010 with MSP430G2553 and F5529, no more I2C patches needed. - Tested with BMP180 and Software I2C http://forum.43oh.com/topic/3777-energia-library-bosch-bmp085-template-library/?p=44410 - Fixed I2C for Energia 0101E0016 by removing ugly hacks from the past from the library code. Tested only with MSP430G2553