How to determine the pinout of an unknown 7 segment display

If you have an unknown 7 segment LED display and you want to use it in your project, you need to determine its pinout. The pinout is the arrangement of pins that connect the display to the power supply and the controller. There are different types of 7 segment displays, such as common anode, common cathode, multiplexed, duplexed etc. Each type has a different pinout and requires a different wiring configuration.

In this blog post, I will show you a simple method to determine the pinout of any 7 segment LED display using a multimeter and some jumper wires. You will need:

– A 7 segment LED display
– A multimeter with a continuity tester
– Some jumper wires
– A breadboard (optional)

The steps are:

1. Identify the number of pins on the display. Most 7 segment displays have 10 or 12 pins, but some may have more or less. The number of pins will help you narrow down the type of display you have.
2. Set your multimeter to diode test mode. This mode will beep if there is a short circuit between the probes and light the LED segment dimly by passing a small current through it. The meter display will show the forward voltage of the LED segment. From this you can work out what the value of the current limiting resistor will need to be for you to use the display in your circuit. Note however this will only work for displays that have one LED per segment. For modules that use two or more a bench power supply set to 12V and a current limit of 20mA will be needed instead of a multimeter. Note the current limit is important otherwise you will damage the LED display. The power supply output will drop to the forward voltage of the LED segment. For example an large display with 4 LED’s per segment will have a forward voltage of around 8.4V.
3. Connect one probe of the multimeter to any pin on the display. This will be your reference pin.
4. Connect the other probe to each of the remaining pins one by one and note down which segments light up on the display. For example, if you connect the probe to pin 2 and segments A, B and C light up, write down 2: ABC.
5. Repeat step 4 for all the pins on the display and make a table of your results. For example:

| Pin | Segments |
| — | ——– |
| 1 | ABC |
| 2 | DEF |
| 3 | G |
| 4 | DP |
| 5 | C |
| 6 | E |
| 7 | B |
| 8 | A |
| 9 | F |
| 10 | D |

6. Analyze your table and identify the type of display you have. There are some clues that can help you:

– If only one segment lights up per pin, you have a common anode or common cathode display. The common pin is the one that does not light up any segment when connected to the probe. If your probe is positive on the common pin then you have common anode. If your probe is negative on the common pin you have common cathode.
– If more than one segment lights up per pin, you have a multiplexed or duplexed display the latter of which are often found in AC powered LED clocks. With these types of display the segment pins are shared between two segments and there are two cathodes (or anodes) which are selected by a microcontroller or more often the two common pins are connected to the power transformer so that on the negative side of the waveform one group of segments light and the others on the positive going side of the AC waveform. The common pins are the ones that light up all or most of the segments when connected to the probe. A multiplexed display will have a segment pin shared between all digits such as A and a common pin for each digit. These are the most commonly found type of displays that have multiple digits.
– If some pins do not light up any segment, they may be unused or for decimal points. If your meter or bench power supply shows a short then the display has two common pins connected together. This is often the case with individual 7 segment displays. Usually it is the middle pins on the top and bottom.

7. Once you know the type of display and the common pins, you can label the remaining pins according to their segments. For example, if you have a common anode display with pin 1 as the common pin, you can label pin 2 as A, pin 3 as B, pin 4 as C, and so on.

8. You can now use your display in your project with the appropriate wiring and programming.

I hope this blog post was helpful for you to determine the pinout of an unknown 7 segment LED display. If you have any questions or feedback, please leave a comment below.

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