This is a common cathode seven segment LED display. So once you connect the common ground pin, all of the LEDs are connected The grounds of the LEDsĪre all tied together. However, on the cathode side, you do not have connectĮach individual LED to ground. LED a and b on, you supply each with the necessary. In order to turn any of the segments on, you supply votlage to the terminal that you want turned on. This is how the seven segment display will appear wired up in a common cathode setup:Īs you can see, all of the positive terminals of the seven segment display are all separate. The LED cathodes are all tied together and are common.īelow is a typical LED display, with each LED segment labeled with an alphabetical character. When you have a common cathode seven segment display, which is an array of 8 LEDs, Is the cathode (the shorter lead), which gets hooked up to the negative voltage or the ground of the circuit. Side is the anode (the longer lead), which gets hooked up to the positive voltage of the circuit. The cathode of an LED is the negative terminal of the LED. There are all types of LED Displays, but as far as wiring and connecting purposes are concerned, there are two main types:Ĭommon cathode LED displays and common Anode LED Displays. LEDĭisplays are used in all types of products, including alarm clocks, scoreboards, and all other signs showing characterīelow is an alarm clock composed of a number of LED displays, showing the time. Assuming the same supply voltage, same base LED devices and the same resistors, the power will be the same. Roger Rowland at 6:46 Where did the statement come from There may be some context behind it. The versatility of a 7 segment display lies in the fact that it can be a numerical value indicator. 17 1 6 3 How could there be any difference Please explain. simulate this circuit Schematic created using CircuitLab The purpose of the resistor is to limit the current, it doesn't matter in which part of the circuit it is located. One of the basic principles of electric current is that the same current flows through all elements that are arranged in series. Range of characters, including all numerical digits from 0-9. 3 Answers Sorted by: 18 There's no difference. On which LEDs are lit determines the character which is displayed on the LED.
It also gives you better control over the two different currents, but it isn't free.Each of the 8 segments that make up the display can be either be on the on state or the off state. Resistors are really cheap (unless you have super high requirements), and a resistor generally doesn't take up a lot of space. Is the cost significant? It really depends. Just be aware that sometimes the arrangement of parts does matter, and other times it doesn't. It's not unreasonable because a typical small LED's current is below the limit of being safe to drive directly from the MCU, but is slightly worry-some if you have a lot of other stuff going on. It's unclear from the original question if the kit/tutorials you're using have this type of LED driving circuit. This is an extra part we would have to have in our design meaning extra cost and space. If we instead moved R1 above Q1 or even above D1, we would have to add an additional resistor between MCU output and Q1 to limit the base current. In the above schematic we are using the resistor R1 to both limit current flowing through the LED as well as limiting the base current (current from MCU output to R1). Simulate this circuit – Schematic created using CircuitLab By cleverly placing the resistor it can serve multiple functions at the same time, thus allowing you to reduce the part count and save some money/space. For example, sometimes people will use a BJT transistor to allow for higher current drives through the LED because micro controller pins are limited to low current outputs. However, there are designs for driving LED's using transistors where choosing where you place your resistor does matter. You have non-reactive components (ideally, which is pretty close to reality) thus any current flowing into the diode/resistor must flow out, thus current would be limited equally well by having the resistor on either the anode or cathode side. Usually as RedGrittyBrick said it doesn't matter.
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