# Posssible Delay for a electric circuit needed

While I know that it is impossible to slow light down I was wanting to delay an electrical response from a diode using either a resistor or a capacitor but I could not remember, which does which. The idea for the product is to create an electric delay on a row of led lights after a flashlight turn on the photoresitors behind them on so we can see it turn on slowly like a light chaser. I was planning on using a led a diode and resistors in a row with appropriate delays. I'd like it to be compact so no mechanical delays. PS: This is behind a opto resistor and am wanting one diode to turn on the row of led's then go down the row as the delay is making them react as if slowly like a gradient.

• What does "a row of led lights to a flashlight turns them on" mean and what does "so we can see it turn on slowly like a light chaser" mean? – Transistor Jun 9 '20 at 17:44
• Light chasers are a led row of lights where they gradually get dimmer. – RedCylon784 Jun 9 '20 at 17:51
• You're looking at delays on the order of 100ms to get a perceptible motion. That's going to be difficult with RC delays and still get enough current to drive the last LED. – Cristobol Polychronopolis Jun 9 '20 at 17:52
• Just need to know if I use a resistor a capacitor or both, also beginning sentence might be unnecessary. – RedCylon784 Jun 9 '20 at 17:52
• Are there small and cheap mechanical switches this is a pet project, and i was wanting a passive delay in response to a photodiode. Also sorry if it doesn't make sense. – RedCylon784 Jun 9 '20 at 18:00

I would use a microcontroller to detect when the photoresistor is illuminated and then digitally turn the diodes on and off. You can program any delay you want.

• Using this answer would I use the direct I think it should go to create the illusion of following a light source correctly? to create a delay why not just use a device on the circuit? is said device too big or in need of a step up? also, if needed i can change the mechanical requirement if I can find some good smaller ones I just didn't want a mess. – RedCylon784 Jun 9 '20 at 18:38
• I just needed to know to use a diode, a resistor, or something else, for the delay in current response... – RedCylon784 Jun 9 '20 at 18:45
• @RedCylon784 You could absolutely build this circuit out of analog components, but I think it will be much more difficult that doing it digitally. Probably you would use transistors or opamps to build delay elements and switch the lights on/off in sequence. – user1850479 Jun 9 '20 at 21:48
• Yes user1850479 seems to understand – RedCylon784 Jun 19 '20 at 19:01

A microcontroller is probably your best best For example, microcontroller senses change in resistor → interrupt → LEDs turning on in sequence. PWM could also be used for dimming the LEDs.

You also get programmable LED strips. A 555 timer delay circuit may also work. Not sure if a capacitor is the best way to go for a project like this

1Meg Ohm resistors and 0.1uF capacitor, into CMOS 74HC14 (hex schmitt inverters), may work.

I' d implement the dimming feature with Pulse_width_modulation into NAND gates and some logic to produce numerous duty cycles.

But the MU idea is more compact solution.

In either case, you need some high-current LED drivers with 33 ohm or 330 ohm current limiting resistors.

For an LED light chaser, have a look here:

https://electrosome.com/led-chaser-ic-4017-ic-555/

It uses a one-hot counter https://electrosome.com/cd4017/ which does the chasing, and a 555 timer as a clock, with which you can set the chase speed.

In your case you might need to add another flip flop to reset the counter. The flop is SET when the opto sensor is hit by light, and RESET when the last LED is illuminated.

• Sorry I used the wrong term(will do best to try to talk to y'all), light chaser was descriptive of what I wish to accomplish, I'm basically trying to do a smoke and mirrors type(descriptive not actual) where the trigger to the optodiode transister has a pause and then a pass to whatever light optodiodes recieve it. It's not literally a light chaser but you should be able to sent light into it and chase it with a light source....again i apologize – RedCylon784 Jun 19 '20 at 18:58