PIR LED increase on-time - Page 1
Forum section: electronics / beginners

author: g3kk0
author_rank: Newbie
timestamp: December 14, 2023, 07:37:23 pm
content: Hi,I have a small LED light with a PIR sensor that I use at night in the bathroom. It was a cheap purchase off AliExpress and I'm really pleased with it except for one thing. The light only comes on for roughly 20 seconds before going off and this doesn't appear to be adjustable. Ideally I'd like it to stay on for a couple of minutes so decided to take it apart to see what I could do. After some searching online I came across a post that mentioned the on/off mechanism might be driven via a capacitor being charged and discharged. When I looked on the board I could see what looked like a single capacitor so I was convinced this was what was happening. I then attempting to use a few different sized electrolytic capacitors (50V 1uF, 25V 10uF, 16V 220uF) to bridge the existing capacitor (which remained in place) thinking they would hold more charge and the led would stay on for longer but it didn't seem to make any difference. Now I'm thinking either I'm using the wrong capacitors or maybe it's a little more complicated and one of the other chips on the circuit is providing the timer mechanism. I've attached some pictures of the board in question. Any assistance would be greatly appreciated.Thanks in advance

author: bookaboo
author_rank: Frequent Contributor
timestamp: December 15, 2023, 10:32:25 am
content: See if you can get the PN off the 8-pin component. Then google the datasheet and share it here. Bonus points for matching the pinout to the other PCB components.

author: g3kk0
author_rank: Newbie
timestamp: December 15, 2023, 10:45:50 pm
content: I did think about doing that but unfortunately the 8-pin chip has no markings (unless they are underneath the chip?). I'm guessing if I'm not able to identify that chip there's probably not much I can do.

author: liaifat85
author_rank: Regular Contributor
timestamp: December 16, 2023, 07:23:32 am
content: Changing just the capacitor might not be sufficient if there are other components involved in the timing mechanism. Experimenting with resistor values in conjunction with capacitors might yield better results.

author: Terry Bites
author_rank: Super Contributor
timestamp: December 16, 2023, 10:09:48 am
content: www.szhaiwang.com/pir_ic/HR008_87.htmlI've seen this ic a few times.I imagine others are prety similar. Hunt down the pin with a cap to ground it and try sticking another one in ll.It'll be the timer or the power pin. Buzzzit out.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 16, 2023, 10:17:44 am
content: The chip seems to be s a different one, as the capacitor is at pin 8 as it looks like.If changing the capacitor did not change the time, there may be no easy way and the time could be more or less fixed from inside the chip. The is a chance the capacitor is just for decoupling.

author: g3kk0
author_rank: Newbie
timestamp: March 29, 2024, 05:22:59 pm
content: The chip appears to be different to the one in the datasheet and @Kleinstein is correct with regards to the capacitor being on pin 8.I've tried adding different sized caps but it doesn't seem to change the behavior so I'm starting to think it's the actual chip controlling the timer.I will try adding a few different sized resisters as suggested and report back.

author: Zero999
author_rank: Super Contributor
timestamp: March 29, 2024, 06:06:01 pm
content: What's on the other side of the board?Have you tried reverse engineering it?Is' possible that 8 pin IC is a microcontroller. To increase the on time, you'll either need to put a delayed off circuit between the microcontroller and switching transistor, or replace the microcontroller with one programmed with your own code.