The BelleVue 7-Segment LED Display
The BelleVue display module is a six digit display module. It uses 7-segment
LED modules and is able to display digits and some alphabetic characters.
The display is controlled by a serial interface that is designed to be as simple
as possible to use. Decimal points can be sent in a string of characters and
will be displayed correctly. The display automatically scrolls left when it
receives more than six characters. There are simple commands for flashing
characters, for displaying custom characters and for addressing multiple
displays. This manual describes how to construct the display.
Contents of Kit
Tools Required
Printed Circuit Board
1kΩ Resistor (R1-R8)
10kΩ Resistor (R9-R14)
100nF Ceramic Capacitor (C1-C3 )
2N4401 NPN Transistor (Q1-Q6)
2-Way Header (PL2 Power in)
3-Way Header (PL4 Serial in)
3-Way Header (PL3 Serial Out)
PIC16F886 Microcontroller (IC1)
3-digit, 7-seg LED (LED1-LED2)
Soldering Iron
Solder
Small Pliers
Wire cutters
Other Items Required
5 Volt Power Supply
Computer or Microcontroller with
serial interface
Figure 1 Completed Circuit
BelleVue 7-segment LED Display
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Serial Input
from PC or
microcontroller
Display Driver
(PIC16F886)
Serial Output
To other
Displays
6-Digit 7-Segemnt LED Display
Figure 2 Block Diagram
Instructions
When soldering a circuit board it is generally best to start with the smallest
components and work up. This means that when a component is loosely fitted
into the board it will lie against the board when the board is turned upside
down for soldering. On the top surface of the board there is a printed diagram,
called a silkscreen that shows where each component is to be located.
Figure 3 Silkscreen Diagram
1. Resistors
There are 14 resistors
in the circuit and they
are labelled R1 thru
R14 on the silkscreen.
Resistors R1 thru R8
are 1kΩ, they can be
recognised by their
coloured bands:
Figure 4 Resistors Fitted
brown, black and red.
Resistors R9 thru R14
are 10kΩ, they can be recognised by their coloured bands brown, black and
orange.
If you are unsure the value of a resistor can be tested using a multimeter in
resistance mode. The leads of the resistors should be bent to allow them to be
inserted into holes 0.3 inches (7.5 mm) apart.
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2. Ceramic Capacitors
Figure 5 Ceramic Capacitors
There are three ceramic
capacitors in the circuit labelled
C1, C2 and C3 on the silkscreen.
The capacitors all have a value of
100nF. The leads should not
need to be bent to be inserted
into the holes.
3. Integrated Circuit Socket
A socket is fitted to the board to hold the microcontroller that drives the
display. The socket has a circular cut-out at one end; this indicates the
orientation of the integrated circuit and should be at the end closest to C1
4. Transistors
There are six transistors in the circuit. The outlines of the transistors printed
on the silkscreen form the shape of a capital letter D. The body of the
transistors is rounded with one flat face so that viewed from the top it has the
shape of the letter D. The flat on the transistor body and the flat on the
silkscreen outline should line up when the transistor is inserted the right way
around. The leads of the transistor must be bent slightly to fit the holes in the
board.
Figure 6 IC Socket and Transistors Fitted
5. Pin Headers
A 3-pin header is fitted to connect the serial input to the circuit; this is labelled
PL4 on the silkscreen. A 2-pin header is fitted to connect the power supply to
the circuit; this is labelled PL2 on the silkscreen. If the serial output of the
display is to be used to control another display then an additional 3-pin header
should be fitted; this is labelled PL3 on the silkscreen.
A header consists of a plastic body with pins running through it. The shortest
end of the pin should be inserted into the board.
6. LED Modules
Two 3-digit LED modules are fitted to the back of the display. The pins of the
LED modules will come through to the component side of the board. Once
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these are fitted it will be difficult to unsolder the other components so it is a
good idea to inspect the circuit carefully before fitting the LEDs. It is important
to make sure that the decimal points are at the bottom of the display.
Figure 7 Front and Back Views with LEDs Fitted
7. Microcontroller
The microcontroller chip is fitted into the IC socket. It does not require
soldering. It is important to make sure that it is fitted the right way around.
There will be a small semi-circular cut-out at one end and this should be
facing towards the capacitor C1 and the serial input PL4.
Figure 8 Pin Header Connections
Connecting the Circuit
Testing
Before testing the circuit check over all the components to make sure they are
in the right place. Check that the microcontroller is positioned the right way
round. Take a close look at all the solder joints. Just one bad joint could stop
the whole circuit from working.
Once the circuit is checked power it up by applying power between Gnd and
Vcc. The power supply should supply between 3.3 and 5 volts and at least
25 mA. When first powered up the display module will show its firmware
version enclosed in brackets. For example: “[0-01]”. If the display powers up
successfully see the operating manual for details of how to control it through
the serial input.
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