Although LCD displays are sometimes preferred due to their low power requirements, low cost, and simplicity of engineering into a circuit, the standard 7 segment LED display is still widely utilized in a significant number of applications because of their higher temperature range, visibility, bright colors, and wide viewing angle. The seven segments in a basic LED display are sometimes labeled as: the letters a to g and dp, where dp is the decimal point. So has a grand total of 8 control lines are required to turn each one of those segments off or on individually by connecting to each of these segments and the decimal point.
There are two sorts of 7 segment displays available, the common anode and the common cathode. The common-anode display configuration has all anodes for each LED wired in common which is then typically connects to the positive voltage supply. The cathode ends of each LED are individually connected to the control lines which need to be current sinks that are switched on and off thru transistors or an LED driver chip. In a "common cathode", the common cathode is routinely connected to ground, and the control lines for each segment are current sources which are used to switch on and off individual segments.
So a seven segment plus decimal point package will only require nine pins, but they typically come in 10-pin packages as the common pin is wired into two pins. Since each one of the segments is really as a forward-biased light emitting, a current limiting resistor is required between the driver transistor and the LED segment to restrict the maximum current flow to a safe value.
An IC driver chip such as the 74LS47 can be used for common anode display types, while a 74LS48 is can be used for common cathode display varients. Most driver chips,eg the MC14511 have a decoder built in, so a binary number input is converted to the seven segment control format.
Some driver chips, for example the CAT4008 or CAT4016 from Catalyst Semiconductor, Inc, update the seven segment control format via a latch hooked up to a shift register, where the binary info is clocked in serially using a single data spin.
A single LED driver chip can drive more than one seven segment display by a strategy called "multiplexing." In this method, the extra displays are connected in parallel, while the "common" line is taken out separately from each display and attached to a switching circuit which turns each line (and hence each display) on and off for a few milliseconds in sequence for each display. This lowers the pin count, but has some disadvantages, for example lower brightness and flickering displays.
There are two sorts of 7 segment displays available, the common anode and the common cathode. The common-anode display configuration has all anodes for each LED wired in common which is then typically connects to the positive voltage supply. The cathode ends of each LED are individually connected to the control lines which need to be current sinks that are switched on and off thru transistors or an LED driver chip. In a "common cathode", the common cathode is routinely connected to ground, and the control lines for each segment are current sources which are used to switch on and off individual segments.
So a seven segment plus decimal point package will only require nine pins, but they typically come in 10-pin packages as the common pin is wired into two pins. Since each one of the segments is really as a forward-biased light emitting, a current limiting resistor is required between the driver transistor and the LED segment to restrict the maximum current flow to a safe value.
An IC driver chip such as the 74LS47 can be used for common anode display types, while a 74LS48 is can be used for common cathode display varients. Most driver chips,eg the MC14511 have a decoder built in, so a binary number input is converted to the seven segment control format.
Some driver chips, for example the CAT4008 or CAT4016 from Catalyst Semiconductor, Inc, update the seven segment control format via a latch hooked up to a shift register, where the binary info is clocked in serially using a single data spin.
A single LED driver chip can drive more than one seven segment display by a strategy called "multiplexing." In this method, the extra displays are connected in parallel, while the "common" line is taken out separately from each display and attached to a switching circuit which turns each line (and hence each display) on and off for a few milliseconds in sequence for each display. This lowers the pin count, but has some disadvantages, for example lower brightness and flickering displays.
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Embedded Adventures is a great website to get information about electronics as well as useful modules such as a 7 segment LED display, or an alphanumeric LED display.
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