![]() ![]() ![]() In this case the data for each digit is set up in turn on D0 to D3 and the digit’s /LE (latch enable) pin is pulled low. By using a 4511 latch per display a flicker-free display is possible.įigure 5 shows how to use a 4511 latch per digit. The 4511 can source or sink current for the displays. This renders the 4511 unsuitable for hexadecimal display. Note that BCD values above ‘9’ are considered void and the display will be blank. Pull low to read the inputs and pass through to the seven segment outputs. ![]() By using the BCD decoder only four lines are required to drive the seven segments. The 4511 BCD to 7-segment latch / decoder / driver.īy using a latch / decoder / driver such as the 4511 decoder ( datasheet) the designer has many more options for display. This efficiency in hardware and PCB layout is what makes multiplexing so popular. Note that 32 segments can be controlled using only 12 outputs from the controller. This is acceptable because the segments will be powered for a maximum of 25% of the time – 25% duty-cycle. When multiplexing displays in this manner it is normal to run at a current higher than nominal. The sequence is run quickly enough that all digits appear to be continuously lit due to persistance of vision. Then the required segments for digit 2 are turned on and Q2 is strobed, etc. The required segments for digit 1 are set on lines A to G and Q1 strobed (turned on briefly). In the scheme of Figure 4 the segments are driven high by the micro-controller. 4-digit multiplexed common-cathode display.īy multiplexing seven-segment displays the number of pins required to drive the displays can be reduced. These have the advantage that, for multiplexed displays, the digit can be strobed using an NPN transistor in the cathode connection to ground. As might be expected, package pin-count is reduced by using a common pin for one side of all the LEDs. Eight pins will suffice for a true seven-segment display whereas nine are required for one with a decimal point. Typically the displays have a common pin for all the LED anodes or cathodes. The standard segment identification is shown in Figure 1 and segments are named A to G starting at the top and going clockwise with G being the centre segment. A limited range of alphabetic characters can also be formed but these are of mixed case and can be difficult to read. The decimal, if supplied, point requires an eight LED.ħ-segment (or “seven-segment) LED displays are commonly used to display digital information. Each segment consists of one or more LEDs and can be lit independently of all the others to form the digits 0 to 9. Standard 7-segment display layout and segment identification. ![]()
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