flyrotary@lancaironline.net Mailing List Archive

Well, for some of you (Kelly?) who have given up on my long delayed effort to "digitize" the analogy fuel monitoring system I developed several years ago there is news. Some of you have seen it hanging in the cockpit from my light dimmer switch. At long last, I am happy to report progress on converting to digital. Actually, took a completely different design approach to capitalize on the capability of a digital chip.

In any case, some of you had expressed an interest in the old analogy system, but I even though I redesigned it twice with the thought of providing systems, it was always too little capability and too many parts.

So I decided to switch from the analog to the digital world {:>)

It was very difficult (for me) to get into learning assembly language for these Microchip PIC microprocessors. They are very flexible devices with all sorts of modules built in - which means a lot to learn.

My old analog fuel monitoring system is very accurate, but it only provided

Fuel_Flow_rate

Total_Fuel_Used

I now have my new digital development system programmed and operating, being fed by an injector pulse train. It at this point provides ( on 3 user selectable screens on a 2x16 backlit LCD )the following:

1. Fuel_Flow Rate

2. Fuel_Used

3. Fuel_Remaining (for those of us who have problem subtracting above 3000 MSL {:>))

4. Time_Remaining (at current flow rate) before Dry tanks (This to keep your heart beating at a faster pace)

5. RPM (to the nearest +- 1 rpm)

6. HP Power (Estimate calculated based on fuel flow rate - mainly just a fun item that was easy to add)

7. Low_Fuel Alarm (Default value is 30 minutes at current burn rate but can be user changed - maybe)

8. Air/Fuel Ratio Indication on LCD (L-------X--------R) with the X position corresponding to the LED lite on the lean-rich line. (Uses the cheap O2 sensor)

It Will save Fuel_Remaining value to EEPROM on engine/power shutdown

Will Retrieve Fuel_Remaining Value upon Power up.

Everything mentioned above is current working on my development board sitting on my bookcase design laboratory.

Still working on how best to input/change data - right now 3 push buttons appear to have the lead

Need this so that user can

1. Can change fuel remaining value (in case someone stole fuel from you tank {:>))

2. Can Add fuel to quantity (preferably after refueling)

perhaps change the Low fuel alarm - I may simply select 30 minutes as I am concerned about somebody intending to put in 10 minutes and putting in 1 {:>) - guaranteed to accelerate the heart rate.

3. A self calibration feature whereby you put in the amount of fuel it took to fill the tank and the chip calculates the difference and adjusts the K factor to close the error gap. This would also take care of aging injectors and different flow rate injectors (up to a point).

My current intentions is to put the unit in a 2 1/4" case provided I can find a LCD or similar display that will still provide readable size Text across the cockpit. Although I could fly with the development system on the passengers seat, I still need to develop the operational board - however, that will be a piece of cake compared to learning to program the chip {:>).

Just thought that some of you would be interested in the update.

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC