Adding a dummy load to 'on at dark' LED circuit - Page 1
Forum section: electronics / beginners

author: Phillipthegreat
author_rank: Newbie
timestamp: February 28, 2018, 05:51:29 pm
content: So I've got a photocell wired to control a wall usb converter powering an LED strip, all behind a small painting canvas, and it pretty much works. However, when the photocell is trying to keep the circuit off, some power still leaks through and makes the lights flicker. I found out that I can add a heavier power load to make this stop, but I don't know what I should use for this dummy load. So I've got two questions: what is the best thing to use for a dummy load, and how heavy does the load have to be? Can I just use something discrete and cheap like a small resistor? I considered using an incandescent light, but I don't want another light.Thanks for any help!

author: sokoloff
author_rank: Super Contributor
timestamp: February 28, 2018, 05:57:32 pm
content: Why not use a transistor as a switch? Control the transistor from the LDR.

author: Phillipthegreat
author_rank: Newbie
timestamp: February 28, 2018, 06:12:58 pm
content: Actually, I just figured out a fix: I had some delay relays that I bought thinking they'd fix the issue, but they didn't fix it at first. I just now discovered that I could wire it through the 'normally open' side of the relay so that the spikes of power wouldn't immediately leak through the relay to the lights. So my main problem is fixed, then.

author: Phillipthegreat
author_rank: Newbie
timestamp: February 28, 2018, 08:06:02 pm
content: Okay, so new problem. When the photocell is under medium light, it makes the lights flicker rapidly. I assume this is because it's using pwm to adjust power throughput. How can I make this flickering not happen? At this point, I'm considering just throwing out the circuitry altogether and using a plug-in timer.

author: sokoloff
author_rank: Super Contributor
timestamp: February 28, 2018, 08:34:42 pm
content: One obvious question: is the light from the LED able to affect the photocell/LDR and cause feedback?

author: Phillipthegreat
author_rank: Newbie
timestamp: March 01, 2018, 04:04:10 am
content: No, I made sure that wasn't an issue, and it flickers with other led lights as well. What was the transistor idea you mentioned?

author: ketimoi
author_rank: Contributor
timestamp: March 01, 2018, 05:50:55 am
content: Recheck your all connection again. You need to use a good led bulb for thishttps://theeffectiveguide.com/best-tactical-flashlight/. I think I read there how to identify a good led lights. However, You need to figure out the relation between the transistor and switch properly. If you are not clear how to use them then it will be difficult to solve your problem.

author: sokoloff
author_rank: Super Contributor
timestamp: March 01, 2018, 02:56:51 pm
content: Quote from: Phillipthegreat on March 01, 2018, 04:04:10 amGoogle "using a transistor as a switch" and find a tutorial that "clicks" with your learning style. It's an extremely common application of a transistor, so there will be 1000s of articles and probably 100s of videos.Here are a couple that on cursory glance seem useful:http://www.dummies.com/programming/electronics/components/electronics-components-use-a-transistor-as-a-switch/But as I said, if those don't "click" with you, there are more than you could possibly read in a lifetime.

author: sokoloff
author_rank: Super Contributor
timestamp: March 01, 2018, 03:00:21 pm
content: https://learn.sparkfun.com/tutorials/transistors/applications-i-switchesAnd perhaps very much "cookbook" for your application:https://www.kitronik.co.uk/blog/how-an-ldr-light-dependent-resistor-works/