|4. The use of a CMOS 4511 BCD to 7 Segment Latch Decoder Driver as part of
This final section of Trial1 uses a CMOS 4511 BCD to 7 segment decoder chip to do what we have been building during this trial. The internal
circuit diagram of the chip in the data sheet shows the decoding circuits for the 7 segments for the digits "0" to "9". Four bits are needed
to encode these digits as binary values 0000 to 1001. This use of 4 bit binary to encode each decimal number is called BINARY CODED DECIMAL,
abreviated to BCD.
The inputs on the 4511 chip marked "A" to "D" are the four bits of the BCD with "A" being the least significant bit. The outputs "a" to "g"
are the seven segment drive signals.
FOR THE REST OF TRIAL1 THE VALUES OF THE FOUR INPUTS SHOULD BE "A" = SWITCH A on the trainer, "B" = SWITCH B on the trainer,
"C" = 0V from the trainer and "D" = 0V from the trainer. THE POWER SUPPLY TO THE CHIP IS CONNECTED "Vdd", pin 16, = +V from the trainer and
"Vss", pin 8, = 0V from the trainer.
There are two different types of 7 segment display, one has all the Anodes of the 7 leds connected together called COMMON ANODE, or CA. The
other type has all the cathodes of the 7 leds connected together called COMMON CATHODE, or CC.
The display we have been working with is a CA type where the display is connected to +V and the segments are lit by connecting each individual
led to 0 V via a resistor. This task in our system was carried out by the PCB with the seven transistors stages. We will still need to use this
PCB between the outputs "a" to "g" on the 4511 chip and the 7 segment display. This is because the chip is designed for CC type displays.
Fortunately, we have the inputs to PCB on the terminal strip, so "a" out from the CMOC 4511 chip goes to "a" on the PCB terminal strip, "b" on
the chip to "b" on the strip ending with "g" on the chip connecting to "g" on the terminal strip and the PCB connects to our 7 segment as
before. The connection diagram in trial1_building has the connections on a prototype board as extra help.
4511 CMOS BCD-to-7-Segment Latch Decoder Drivers
The NOT LT is a LAMP TEST and will put all the segment outputs HIGH to test the led display when connected to 0V, and work normally when it is
connected to +V. NOT BL is BLANKING and will force all segment ouputs LOW to the led display when connected to 0V, and work normally when it is
connected to +V. The LE / NOT STROBE is LATCH ENABLE when connected to 0V and STROBE when connected to +V. In this trial we will connect it to
0V. This "enables" segment outputs to react instantly to changes in the inputs A, B, C and D. The LATCH will be the first circuit to be examined
in trial2 and details of how it works will be covered then.