Simplest LED blinker with added fade - wil it work? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 01, 2021, 04:28:06 am
content: I have tried to simulate a super simple LED blinker on falstad:https://tinyurl.com/yaa5lwly, but it doesn't seem to work.The relay on the left are meant as a replacement for a motor power switch, when the motor is running shall the LED blink or else just glowing constant.Together with the blinking LED, have I added a capacitor that are meant to add a "softener" so the LED is not just blinking, but sort of fade in and out.

author: ledtester
author_rank: Super Contributor
timestamp: January 01, 2021, 04:48:18 am
content: Where's the power source for the LED???Ok, nvm I see it now.

author: ledtester
author_rank: Super Contributor
timestamp: January 01, 2021, 05:15:28 am
content: Is your design is based off the one transistor flasher like this one:http://hobbyelectroniccircuit.blogspot.com/2013/09/single-transistor-led-flasher.htmlThis is a very unconventional use of a BJT transistor which falstad may not simulate correctly.

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 01, 2021, 07:11:05 am
content: Hi thanks for answering:-)My design is inspired by this set of pictures:https://blog.jongallant.com/2015/01/simple-blinking-led/

author: ledtester
author_rank: Super Contributor
timestamp: January 01, 2021, 09:05:46 am
content: Here's another eevblog forum thread on this circuit:https://www.eevblog.com/forum/beginners/weird-one-transistor-led-blinker-circuit/If you peruse the comments of one of the links mentioned there:http://www.kerrywong.com/2014/03/19/bjt-in-reverse-avalanche-mode/you get the impression that even LTSpice needs help to simulate the circuit correctly:Quote

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 01, 2021, 10:04:08 am
content: You are of great help!! Thanks:-)To me does it sound like a bad way to make a blinking circuit, it depends on braking a BJT, and it can't be particular predictable or long-lasting.My "problem" is that the THT circuit, have to be as small as possible, it has to blink-fade 2 a second when the motor is turned on.Two BJT's do not take up any space but to many capacitors do take up a lot of area.Any idea of the best solution?

author: ledtester
author_rank: Super Contributor
timestamp: January 01, 2021, 11:26:42 am
content: Quote from: FriedMule on January 01, 2021, 10:04:08 amUse a small form-factor microcontroller. There are 6-pin SOT23 mcu's available such as the PIC10F or ATTINY10.

author: ledtester
author_rank: Super Contributor
timestamp: January 01, 2021, 11:54:55 am
content: Quote from: ledtester on January 01, 2021, 11:26:42 amWell, having said this I just ran across this breathing LED design which might work for you:https://diyodemag.com/projects/kids_basics_breathing_led_light_555_timer

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 03, 2021, 09:56:27 am
content: Sorry for my late reply, did not get info of your reply.I am hoping for a super simple solution with as few components as possible.I have tried to simulate these two circuits, but they don't seem to work, is it me or the simulator?https://tinyurl.com/ycav3td2EDIT: Forgot to write that the voltage is set to 12V but should in fact be 5V, and I am aiming for 2-3 Hz blink.

author: ledtester
author_rank: Super Contributor
timestamp: January 03, 2021, 10:21:13 am
content: For circuits that rely on this kind of avalanche breakdown your best bet is just to build the circuit and see if it works.Edit: The circuit on the left is a thyristor made from a PNP and NPN, but there is no gate impulse to trigger it.

author: ledtester
author_rank: Super Contributor
timestamp: January 03, 2021, 11:26:37 am
content: Here's a pretty good explanation of how the PNP+NPN combo is meant to work in the left circuit:https://electronics.stackexchange.com/questions/344321/can-a-thyristor-be-built-from-two-transistorsandhttp://www.talkingelectronics.com/projects/TheTransistorAmplifier/TheTransistorAmplifier-P2.html#Latch

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 03, 2021, 12:11:31 pm
content: Thanks, I'll 100% read both!I thought that the PNP on the left was constantly on, since it has 12V from the battery, via the LED.All I have been doing is to go on the internet, select a circuit that was shown to work, but it does not work on the simulator. And yes to build it would be best, I do just not have access to my little shop for the moment.

author: ledtester
author_rank: Super Contributor
timestamp: January 03, 2021, 07:15:00 pm
content: A PNP will turn on if there is current from the emitter to the baseto ground. But the only way from the PNP's base to ground is via the NPN. And the only way the NPN can turn on is if it has base current. But the only source of base current is from the PNP. But the PNP can't turn on because it's base current needs to flow through the NPN to get to ground.However, a small impulse of current through the NPN's base will unblock this situation and current will flow through the PNP-NPN pair, and the current through the NPN will keep the PNP on which in turn keeps the NPN on so you have a latching circuit. Until current through the pair is interrupt via a switch or by removing the power source.