LED open and short detection

Ask QuestionAsked todayActive todayViewed 67 times0

Can someone tell me on what how to detect a short circuit and LED open circuit for the below circuit?

Is it possible to detect which LED?

Could someone provide a circuit which would help to detect an LED short circuit or LED open circuit if all the below LEDs are connected in series as a single string?

I just require a circuit which will detect LED Failure (LED open or LED Short) when the LEDs are working during its normal operation.

voltageledcurrentresistorsdiodesShareCiteEditFollowFlagedited 12 hours agoasked 16 hours agoNewbie1,00044 silver badges2424 bronze badges

• My first thought is to use the following: 74HC244; 74HCT244 Octal buffer/line driver; 3-state:assets.nexperia.com/documents/data-sheet/74HC_HCT244.pdf.TIP30x can be inputs to the buffer. – tlfong01 15 hours ago   
• 1@tlfong01 , the link is not working. Could you tell me how to use this IC and how will it help to detect the open and short condition? – Newbie 15 hours ago
• What does “help to detect” mean here? How do you expect the “circuit” is going to inform you that an LED has failed? Exactly what information do you expect the circuit to provide, and in what form? – Elliot Alderson 12 hours ago
• You didnt mention what is desired output of watch circuit (0V ok and 5V fail, some Led visualization?) Simplest open Led detection is cross the Led with D+Led, or cross with blue. – Michal Podmanický 12 hours ago 
• I just need some indication. Like assume I have some microcontroller pins according to the number of LEDs. So, I need a circuit that will convey the Open or short to the Microcontroller – Newbie 12 hours ago
• Add all of these details to your question. Don’t make the reader sift through all of the comments for important information. Do you want to know if an LED is open or short, or just if it has failed? – Elliot Alderson 12 hours ago
• If you have uC, just measure with ADconverter BG_SUPPLY and anode voltage. If BG_SUPPLY is 5V and anode also 5V, the Led is open. Of course apply some tolerances. – Michal Podmanický 12 hours ago
• The same for short. If BG_SUPPLY is 5V and anode less than 1V the Led is shorted. – Michal Podmanický 12 hours ago
• #Newbie, Welcome and nice to meet you. First thing first: My apology for the bad link. Your following question: “Could you tell me how to use this IC and how will it help to detect the open and short condition? sounds like a newbie problem. I think I need to think a bit thoroughly before I can write up a question at newbie level. Luckily It is locking down holiday today. So let me take it easy and give an answer that even newbies can easily understand. Stay tuned. Cheers. – tlfong01 4 hours ago   

Add a comment

2 Answers

ActiveOldestVotes3

Connect the black (COM) lead of your voltmeter to ground. Now, connect the red (+V) lead to each of the test points, TP7301 through TP7303, in turn. If the voltage you read is equal to BG_SUPPLY then the LED is open, if the voltage you read is zero then the LED is shorted. Since each test point corresponds to a single LED, it is clear which of the LEDs has failed.ShareCiteEditFollowFlaganswered 16 hours agoElliot Alderson23.5k44 gold badges2020 silver badges4949 bronze badges

• @Newbie “detect […] if all the belpw LEDs are connected in series” – the same should work if the LEDs are connected in series, so you would read BG_SUPPLY on open and 0V on closed LEDs. You have to place TPs between all the LEDs. – Sim Son 15 hours ago
• @Elliot Alderson, No, I am asking like, is there a circuit which can detect the LED OPEN OR SHORT during the circuit working conditions. – Newbie 15 hours ago
• 1@Newbie You need to edit your question to clarify what you want. How exactly is this “circuit” supposed to let you know if an LED has failed? – Elliot Alderson 12 hours ago
• Sure, sorry, let me edit my question – Newbie 12 hours ago
• I’ve edited my question – Newbie 12 hours ago

Add a comment1

Question

How to design an alert system to do the following:

1. Detect if any one or more of the LEDs below are open or short circuited,
2. Report the bad LEDs, if any, and whwther they are open or shorted.

Answer

1. To make things as simple as possible, the OP’s specific circuit is abstracted and generalized below.

2. But the OP’s specific LED is not going to be generalized, but would be studied in detail, because the LED’s specific I-V characteristic/parameters are critical in the circuit design.

LED Spec summary and assumption

The design parameters used would be the following:

2.1 Forward LED current I = 10mA

2.2 Forward LED voltage V = 3.1V

Power LED Lamps are usually of the power 1W or 3V, and current 350mA to over 1A. So I assume that the OP’s LEDs are just typical indicator/status LEDs, though not in classical Red, but fashionable White.

I made another assumption that the Vcc is = +5V, as can be inferred from the current of limiting resistor of value 1k2.

3. What voltage level at the test points T1, .. T8 will be if a LED is open or shorted? This question is too simple, so I won’t bother to explain, or my reputation would be damaged. Anyway, the following is a summary.3.1 If a LED is open, corresponding test point would show approx 5V.3.2 If a LED is shorted, it will be approx 0V.In short, simply 5V TTL logic.

4. So the OP’s problem boils down to simply the following:How to read 7 TTL 5V logic High Low signals using 5V Arduino or 3V3 Rpi?4.1 For 5V Arduio, it is a piece of cake: Just use 7 Arduino GPIO pins to direct read the High/Low levels at the 7 test points, and day is done.4.2 For 3V3 Rpi (or similar 3V3 guys), a convert/shift down chip is need to setp down the 7 test points logical level to 5v to 3V3 (See Appendix A for more details). Then the 7 shifted down test point signals can direct connect to Rpi to read.4.3 For either Arduino or Rpi, if there are not enough GPIO pins to go around, the OP can consider using GPIO pins extenders such are MCP23008 (See Appendix B for more details.)

References

(1) LED VCEW1151CDS-3BZH3 Product Sheet – Stanley

/ to continue, …

Appendices

Appendix A – Logical level signal up/down converter/shifters

/ to continue, …

Appendix B – GPIO Pins Expanders

/ to continue, …

ShareCiteEditDeleteFlagedited 1 min agoanswered 1 hour agotlfong011,68611 gold badge66 silver badges1111 bronze badgesAdd a comment