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. 7-segment display basicsħ segments Figure 1. If switching is not required then it can be omitted and the LED cathode connected to ground. If used it will drop about 0.2 V when on and this could be subtracted from the R1 calculation above. The nearest standard value is 10 Ω and this would be fine. We can calculate the value of R1 from the voltage drop across it and the current through it:įor a 5 V supply this would give R1 = 9 Ω. 1602 LCD backlight current limit and switch. If connected directly to a 5 V supply then excessive current would flow (as predicted by the IV curves), the backlight would be destroyed and the display ruined.Ī simple LED current limiter will suffice. It appears that the LED has a forward voltage, \( V_f \) of 4.1 V at 100 mA but that there is no current limiting built in.
The backlight is nominally 5 V but reading the datasheet gives some warnings. The popular TC1602A-01T LCD features an LED backlight.
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