flowmeter.pdf

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A GAUGE FOR ULM (ULTRA-LIGHT AIRCRAFT)
H ISTORY
A friend of mine is building his ULM and he would like to know his consumption of gasoline, so we
looking for how to do :
W HAT WE NEED
-
an ULM always take of with a full tank.
The consumption is about 6-7 litres per hour
-
A bar-graph will be great (easy to read)
-
But to know the quantity staying will be good
-
An idea of the instant consumption will be a +++
-
Something indicates that the gauge is working is necessary.
-
At the end two alerts for the end of the tank are a nice idea.
-
We take the flowmeter Digmesa FHKSC which drives a
hall effect transistor giving nice pulses.
1800 pulses per litres with a flow rate of 0.025 to 2
litres/minute
_______________________
P OWER SUPPLY
Very classical we add a fuse between the battery and the switch
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DIAGRAM
We use an ATMEGA 8 which uses is internal oscillator and we add Xtal of 32768 Hz for the clock to
know the instant consumption. The ports are used as following:
6 ports for the LCD on port C
1 port INT1 portD.3 received the pulses of the flowmeter
2 ports PortB.6 et portB.7 for the timer crystal
we use the Brown out for reset
the other ports are in input and wired to the ground.
We follow the data sheet of the flowmeter to use it : 1 R pull-up of 4.7 K and 1 C of 100nF (signal and
ground)
_______________________
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P ROGRAM
Calculation
They are very simple and explain with the rem of the program
The instant consumption is an average on 10 seconds : 10 measures divided by 10
The volume staying in the tank is decremented by the interruption, we use a format statement.
The most difficult is the bargraph, but I let you trying to understand !
U SE OF THE LCD DESIGNER
Five are used for
the bargraph
Two are used to
put a small whell
showing the
flowmeter running,
see the LCD.
The good running indicator
It is the last character of the first line, this character change all ½ second if the flowmeter is running
well.
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THE PCB
Some remarks
C5 et C3 are not necessary if
your crystal is good .
C8 is necessary if you use a
long cable.
The SIL 16 connector is used
by a standard LCD
R3 could be adapted.
MATERIAL LIST
Type
Designation
Resistors
R1
470
R2
4.7 K
R3
100
Potentiometer RV1
10K
capacitor
C1
220 µF
C2
220 nF
C4 – C6
100 nF
C3 – C5
22 pF
IC
U1
ATMEGA8 Atmel
U2
7805
Diodes
D1
1N4004
D2
Led
Xtal
X1
Quartz horloger 32768hz
LCD
LCD 16X2 retro
Selectronic 50.6672
flowmeter
F1
Digmesa FHKSC 932-8501
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