How to delay a LED?? (On/Off)

I need to at least delay my LED.

I'm ONLY allowed to use BJT and resistors. ( No Diode, Relay, Capacitors and IC's etc.)

Details: there are 7 LEDS in total.

There are 7 levels in the container which the led's indicate.

If the container is "empty" the 1st led is "on".

If the water reaches to the 2nd led/level, "on" and the 1st led will turn off.

3rd led/level = On ; 2nd and 1st = Off

4th led/level = On ; 3rd, 2nd, 1st = Off

5th led/level = On ; 4,3,2,1 = Off

6th led/level = On ; 5,4,3,2,1 = Off

If the water reaches to 7th led/level all led's is "Off" but after a delay in (secs, milliseconds) all the leds will turned "On"

I need any kind of help or advice to do this project. thankyouu!

by amsnklmf
March 13, 2019

resistor and transistor don't have delay function.

by wangwg88
March 13, 2019
Add comment...

Please sign in or create an account to comment.


3 Answers

Answer by amsnklmf

Please help

+1 vote
by amsnklmf
March 13, 2019

I couldn't attach picture of circuit. you can tell me your email.

by wangwg88
4 days, 16 hours ago
Add comment...

Please sign in or create an account to comment.


Answer by wangwg88

you may use millions pieces of BJTs and resistors to make the delay circuit, but it never happens in actual circuit.

+1 vote
by wangwg88
6 days, 13 hours ago
Add comment...

Please sign in or create an account to comment.


Answer by Negativ3

Needs a timer circuit on the output to LED 6 so when it goes off (LOW), the timer is initiated, then "enables" all LEDs after a pause. Difficult to be more exact without seeing a circuit diagram Have a look at 555 timers.

+1 vote
by Negativ3
10 hours, 47 minutes ago
Add comment...

Please sign in or create an account to comment.


Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account


Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers


Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.


About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.