Download Presentation 2

216.382 Microcontroller Application – Group A
Project: Water flow meter
Presentation
Introduction:
Group A’s project is to design a ‘Water Flow Meter’ for a rain water system.
The water flow meter is an important aspect of the system as it can be used to monitor
the influx of rain water into the system when attached to the input pipe, or ensure
faultless supply of the water when attached to the outflow pipe of the system.
Design Overview:
The design focus for this project was the relationship that DC voltage output is
proportional to the speed of rotation of the generator.
E= Blv
Where: E is the induced e.m.f
B is the flux density (T)
l is the length of the conductor in the magnetic field (m)
v is the velocity (m/s)
The varying DC voltage with speed could then be used as the analogue input into the
microcontroller and converted into a digital signal to drive a seven segment display.
Block Diagram:
Analogue Input
First
Motor
Second
Motor
(Turbine)
(DC generator)
Filter &
Protection
Power
Supply
10V
Group Member: Mantang KE, Dan, Jia Xu
MICRO
ADC
seven
segment
display
µPC78L05J
5V Regulator
Page 1 of 7
216.382 Microcontroller Application – Group A
Project: Water flow meter
Presentation
Hardware Design:
Lab Tests:
The DC Generator Output
The picture below shows the DC generator output before any signal
conditioning circuitry is added. The oscilloscope shows an inverted full-wave
rectified output; note the amount of noise evident in the waveform. Further
testing showed the DC content of the waveform increased as the RPM of the
generator increased.
Group Member: Mantang KE, Dan, Jia Xu
Page 2 of 7
216.382 Microcontroller Application – Group A
Project: Water flow meter
Presentation
Analogue Input Circuitry:
The actual system uses a turbine as a mechanical transducer, converting the
movement of the water into mechanical energy; this in turn drives a small DC
generator (DC motor working in reverse). In order to replicate the turbine an
additional small DC motor is used to provide the mechanical energy to drive the
DC generator. Upon measuring the output of this signal with the oscilloscope,
we found that it was necessary to add the following signal conditioning
components:
1. Cnoise - 0.01µF noise suppression cap
(see microcontroller).
2. D1diode - Back EMF protection diode.
This is used in case the turbine suddenly stops due to a foreign object in
the water supply, thus causing an instant collapse of the magnetic field
of the generator inducing a high voltage reverse polarity spike
(V= -L di/dt) potentially damaging the microcontroller.
3. Cfilter - reservoir capacitor.
To smooth the full-wave rectified voltage output from the DC generator.
This capacitor value was found via experimentation in the lab using
range of capacitor values. The 470µF capacitor gave the required
smooth DC output voltage. (Xc = 1/2πfC) as capacitance increases
capacitor reactance decreases thus filtering the ripple frequency. Also
the formulae for voltage in a capacitor V=Q/C, where Q is charge loss,
shows as the capacitance increases the voltage reduction decreases.
Working voltage of the capacitor should be ≥ 10V
4. D4diode & D5diode - Input protection circuit
Protection for the A/D converter and the HC08QY4 microcontroller (a
clamp system), consisting of two diodes- it clamps the voltage input
range to approximately 0V – 5V. If the analogue input increases to 5.6V
the upper diode will conduct clamping the input to the +5Vsupply rail,
if the input drops below 0V to -0.6V then the lower diode conducts
clamping the input to ground potential.
(Note all diodes rated at 7A insures that they will adequately handle any high currents)
Group Member: Mantang KE, Dan, Jia Xu
Page 3 of 7
216.382 Microcontroller Application – Group A
Project: Water flow meter
Presentation
Schematic Diagram of analogue input
Group Member: Mantang KE, Dan, Jia Xu
Page 4 of 7
216.382 Microcontroller Application – Group A
Project: Water flow meter
Presentation
HC08QY4 Microcontroller:
The conditioned analogue signal of this generator must be measured by the
HC08QY4 microcontroller and display it on a 7 segment display. This can be
done by using one of the six ADC converter channels and using one of the
output ports to drive the display
The output pins of the microcontroller are limited to about 20mA sourcing &
sinking current (possibly a little more with sinking)
1. Pin 12 is used as the analogue input on the microcontroller as according
to the data sheet this pin has a priority for Analogue to Digital
conversion. The rest of the functions of this pin will be disabled by the
software program i.e. keyboard interrupt etc.(pg 20 of data sheet)
2. According to the datasheet (p46), a 0.01uF capacitor can be used to
improve the performance of ADC by reducing noise; it needs to be
placed as close as possible to the package pins. Since the microcontroller
board is already populated, the cap was placed at the source of the noise
i.e. at the DC generator.
3. The analogue input voltage to the microcontroller must lie between
VDD and VSS in order to give an accurate conversion; hence the
clamping helps insure this (pg 37). The analogue to digital conversion
will be done in the 8-bit mode, since we only have a 7 bit output to the
display.
4. Port B (B0-B7) will be configured as an output via the DDR data
direction register and used to drive the display with B7 used to switch
between the two seven segment displays, since B7 is just the decimal
place LED.
5. The power supply for the micro is provided by the µPC78L05J 5V
regulator; this nominally works of a 10V supply according to its data
sheet. It is vital to put a 0.1µF across VDD and VSS pins of the
microcontroller (this is provided by the board design already). The
following caps and diodes may be required to protect against the power
supply used with the project.
Group Member: Mantang KE, Dan, Jia Xu
Page 5 of 7
216.382 Microcontroller Application – Group A
Project: Water flow meter
Presentation
6. All unused pins of the microcontroller will be made an input and
internally held high by the pull up enable registers, as unused pins must
never be connected directly to the supply rail or ground.(pg 20 of data
sheet)
Group Member: Mantang KE, Dan, Jia Xu
Page 6 of 7
216.382 Microcontroller Application – Group A
Project: Water flow meter
Presentation
Display Output:
Schematic Diagram
 Seven segment display output
Components Chosen
R0 to R6 are all have the same value; they are used to protect the
microcontroller output by limiting the output current to less than 20mA.
Typically 10mA into each LED branch in the 7-segment display (Internet
source) so in this case we will use 10mA.
R
V 5  1.2  0.2

 360
I
0.01
So, Ro, R1, R2, R3, R4, R5 and R6 are 360 ohms.
BC327 is a genetic PNP type transistor. It has absolute maximum Ic of 800mA,
at saturation Ib=-50mA and Ic=-500mA
R
V
5

 100
I 0.05
So, Rb =100 Ohm.
Since total current from 7-segment pass through transistor is 7x10mA=70mA,
Rc or the load resistor is not required as the current is limited at the
microcontroller end.
Group Member: Mantang KE, Dan, Jia Xu
Page 7 of 7