Quote:
Originally Posted by Quezacotl
It is just logic-ic, 4011, NAND gates in a row. I made it like this, truth table:
00 0
10 1
01 0
11 0
Meaning it just subtracts outgoing fuel from ingoing.
I have it installed now in my car, and seems to work properly, no crazy jumping with instant reading, it's stable enough.
Until now, it seems to work, but i will test it with couple of tanks to see if there's something.
I will have over 500km driving at this weekend, so that is a good testing time 
But funny that when i turn the key, but not start, it shows that fuel is used. At the same time when i can hear a short "whrr" from under the hood.
I did'nt know that the car pumps a little amount of fuel every time i turn the key. But that's logical, you can't start sparking with no fuel.. |
From the truth table it seems that pulses from the second flow meter are completely ignored.
A bit of theory...
Let's say that engine is using the amount of fuel corresponding to one pulse per minute, but fuel pump is pumping 6 pulses per minute. So during a minute of driving you should read 6 pulses from the first flow meter and 5 from the second one, right?
So in one minute the table of pulses would look like below
| seconds | FM#1 | FM#2 |
0
| 0
| 0
|
10
| 1
| 0
|
12
| 0
| 1
|
20
| 1
| 0
|
24
| 0
| 1
|
30
| 1
| 0
|
36
| 0
| 1
|
40
| 1
| 0
|
48
| 0
| 1
|
50
| 1
| 0
|
60
| 1
| 1
|
total
| 6
| 5
|
6-5=1 pulse FE
And with your truth table
| seconds | FM#1 | FM#2 | pulses for MPGuino |
0
| 0
| 0
| 0
|
10
| 1
| 0
| 1
|
12
| 0
| 1
| 0
|
20
| 1
| 0
| 1
|
24
| 0
| 1
| 0
|
30
| 1
| 0
| 1
|
36
| 0
| 1
| 0
|
40
| 1
| 0
| 1
|
48
| 0
| 1
| 0
|
50
| 1
| 0
| 1
|
60
| 1
| 1
| 0
|
total
| 6
| 5
| 5
|
total pulses sent to MPGuino 5
So counted FE is 5 times bigger!
I think that simple NAND logic is not enough to do the job. It has to be a time related function. IMHO best way to do that will be to count time between pulses on both FMs. Then just counting the difference.