| I enjoy tinkering with electronics as a hobby so after switching to ethanol I decided I wanted to know the ethanol content from the local pump. There's all ready some nice options out there for e-content gauges...dynosty, zeitronix, and haltech come to mind. I built mine for less then $100 including the GM flex sensor. The GM sensor also tells you the fuel temperature so I added code to display that as well. While I was at it I decided to tap into the ecu's coolant temp sensor wire and display that too. It could still use some firmware tweaks to improve sampling but since I've recently decided to build a new gauge that will interface directly with the consult port I won't be messing with this anymore. Some tech info:
GM sensor outputs a 5volt square wave signal. The frequency of the the signal tells you the ethanol content. The pulse width tells you the fuel temp. 50 Hertz indicates 0% ethanol, and
150 Hertz indicates 100% ethanol. 1 millisecond indicates -40°C (-40°F), and
5 milliseconds indicates 125°C (257°F). The ecu's coolant temp sensor varies in resistance based on temperature. It is not linear. I use a look up table and interpolation to determine output temp. All controlled by a microchip 18f252 microcontroller at 4mhz. It's been a huge learning experience for me. Learned a lot about automotive transient voltages and noisy environments. Building hardware to run in a noisy automotive environment is nothing like my past bread board-lab projects. [ http://i13.photobucket.com/albums/a280/evan3/69CAC441-5DA3-41EA-B8A7-52844309995C-1992-00000168E6DEC854_zps0330209c.mp4 ] 
[ http://i13.photobucket.com/albums/a280/evan3/69CAC441-5DA3-41EA-B8A7-52844309995C-1992-00000168E6DEC854_zps0330209c.mp4 ]
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Built a ethanol content gauge for fun - 
