Although LCD displays are often preferred due to their low power requirements, low cost, and straightforwardness of planning into a circuit, the standard seven segment display is still usually employed in a substantial 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 usually labeled as: A, B, C, D, E, F, G and also DP, where DP is the decimal point. So has a grand total of 8 control lines are wanted 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 often come in 10-pin packages as the common pin is wired into two pins. Since every 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 like the 74LS47 can be employed for common-anode LED types, while a 74LS48 is employed for common-cathode LED types. Most driver chips, such as the MC14511 have a decoder built in, so a binary number input is converted to the 7 segment control format.
Some driver chips, eg the CAT4008 or CAT4016 from Catalyst Semiconductor, Incorporated, update the 7 segment control format through a latch attached to a shift register, where the binary data is clocked in serially thru a single pin.
One LED driver chip can drive more than one 7 segment display by a method called "multiplexing." In this strategy, the additional 7-segment displays are connected in parallel, while the "common" line is taken out separately from each display and hooked up to a switching circuit which turns each line off and on for 1 or 2 milliseconds in sequence for each display. This lowers the pin count, but has many drawbacks, eg 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 often come in 10-pin packages as the common pin is wired into two pins. Since every 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 like the 74LS47 can be employed for common-anode LED types, while a 74LS48 is employed for common-cathode LED types. Most driver chips, such as the MC14511 have a decoder built in, so a binary number input is converted to the 7 segment control format.
Some driver chips, eg the CAT4008 or CAT4016 from Catalyst Semiconductor, Incorporated, update the 7 segment control format through a latch attached to a shift register, where the binary data is clocked in serially thru a single pin.
One LED driver chip can drive more than one 7 segment display by a method called "multiplexing." In this strategy, the additional 7-segment displays are connected in parallel, while the "common" line is taken out separately from each display and hooked up to a switching circuit which turns each line off and on for 1 or 2 milliseconds in sequence for each display. This lowers the pin count, but has many drawbacks, eg lower brightness and flickering displays.
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Embedded Adventures is a cracking website to get information about microcontrollers as well as fun modules such as a 7 segment LED display, or an alphanumeric LED display.
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