My view on life, in any field, is not to produce more but to consume less. Everybody told me this is a very eccentric weird mentality. Perhaps they are right. Nevertheless I have to build my project to make a highly efficient, extremely low drain, motion triggered 12V battery powered dimmable COB LED light for a room. That’s a mouthful I know. Sorry. I have STPD and paranoid fear of not being understood. My battery is charged by a solar panel. But that’s not important for now. I don’t want to use switches, potentiometers or relays. Let’s eliminate those from the start in any design. I also want to consume minimal power. When I enter the room I want the light to automatically turn on. When I leave the room, after 1-2 seconds the light turns off by itself. I don’t want any switches or potentiometers, If light too bright or too dim, I want a touch sensitive surface in rare occasions to control the dimming. The entire assembly will be mounted in a box on the ceiling of the room (except the battery of course).

In my mind there’s this logic diagram with 4 basic minimal components: logic block diagram

  1. 12V battery
  2. PIR motion sensor HC-SR501 (with BIS0001 IC and a HT7133-1 3.3V 30mA voltage regulator onboard) . The module has the jumper set to repeat trigger mode. Has 3 connecting pins: ground pin, input voltage(4-24V DC) and Output pin with a 3.3V TTL positive logic output, LOW=no motion, HIGH=motion has been detected). The sensor will have to be continuously powered forever. I’m ok with that, since it draws under 50uA quiescent current. Pot1 CW direction increases ONTIME when motion has been detected. Pot2 CW direction increases the area of detection (from 3 up to 7meters) Datasheet here> https://www.mpja.com/download/31227sc.pdf
  3. FC-106 Touch LED dimming PWM light regulation module with onboard SGL8022W IC. The onboard SMD LED is removed. The onboard S8050 Y3J NPN transistor (https://www.sunrom.com/get/448000) rated for 40V 0.5A might be small, if so, it can be replaced with a bigger one. No problem there. The FC-106 jumpers are extremely and very carefully set (T1=1 and T2=0) to regulate lightness continuously with lightness-MEMORY meaning the light level when LED being turned off is stored in memory,which will be set as the initial lightness when next touch operation turning on the LED. This is crucial. If power to the module is completely cut off, the stored light level will be lost, therefore the SGL8022W IC will have to be continuously powered forever. I’m ok with that, since It only draws 12uA on standby. Datasheet here> https://datasheet.lcsc.com/szlcsc/Sigma-Micro-SGL8022W_C81650.pdf
  4. And finally 120mmx36mm 10W 12V COB White LED. Main schematic

I don’t want to ditch the FC-106 module to design a different PWM block dimmer controlled by a potentiometer as a normal individual would think of doing. I’m not normal. I have issues. I have an allergy to potentiometers. They are prone to failure after a few years due to dust, moisture, grease or other mechanical failures. I want something that is maintenance free and lasts thousands of years. I’m crazy, I know. We live in the 21 century. Let’s keep up the pace and use touch sensors instead of switches. Call me a germophobe weirdo if you want. I don’t care.

SGL8022W internal schematic

The dimming of the 12V COB LED works flawlessly. Why it’s sold as “undimmable” is way beyond my comprehension. The maximum current I was able to measure was 0.8A at 12.9V meaning 10.32W. Math checks out. The onboard S8050 Y3J transistor gets warm but didn’t got upset since the SGL8022W when first powered automatically starts from half level light and not full power. That transistor is the least of my problems with this project. The problem I’m facing is interfacing the PIR sensor with the dimmer. I’ve managed to solve half of the problem by sandwiching the touch sensor module between 2 capacitor plates and a thin dielectric film not seen in the attached picture. Applying at least 1.5V on this makeshift plate capacitor seem to trigger the SGL8022W chip. (I took care of not touching the wires going to my makeshift plates)

This only solve half of the problem because I still need some sort of “buffer” between the PIR sensor and the dimmer. They don’t speak the same language, so I need a “translator”. Excuse my weird terminology. English is my 2nd language.

Somehow interfacing directly to the touch capacitive sensitive pin 5 of the SGL8022W IC ideea did cross my mind but I have to keep in mind that I don’t want to discard the touch sensitive area of FC-106 module, because I still want to occasionally manually control the dimming. And besides the signals are not compatible (see picture of signals required). According to SGL8022W IC datasheet a short pulse less than 550ms is required to turn on/off the light. More than that will dim the light. Thus the interface circuit will have to put out a pulse with the width less than 550ms (RC time constant).

I’m thinking along the sides of a both rising & falling edge retriggerable one-shot. I’m ok with building complex circuits, however, since there might be an easier alternative, I have to explore it. I sense there’s a simpler solution for my project, which is why I’m posting on this forum. I know I’m missing something.

Thus I was thinking, why can’t I use this type of circuit to act as my interface between PIR sensor and touch dimmer? Possible interface

I need some help. It took me 6 hours just to compose, write, draw and raise this question on this forum. Please show me the courtesy for all my work and reply more than a few words, a sentence or a question. Thank you.

TL;DR: Interface a 3.3V TTL logic signal, to a touch sensitive capacitive pin, by doing a signal conversion of the input raising and falling edges into short 200ms pulses.

  • 3
    \$\begingroup\$ I stopped reading as soon as you said My view on life - get to the point and minimize to a simple EE question is my advice. \$\endgroup\$
    – Andy aka
    Apr 28 '20 at 10:29
  • 1
    \$\begingroup\$ "When I enter the room I want the light to automatically turn on. When I leave the room, after 1-2 seconds the light turns off by itself." A motion sensor is not a presence sensor. With your plan the light will switch off 1-2 s after you stop moving in the room. \$\endgroup\$
    – Transistor
    Apr 28 '20 at 10:56
  • \$\begingroup\$ You want something that lasts a thousand years with no maintenance but you are using a lead-acid battery? You are going to have a touch switch mounted in a box on the ceiling? I don't think your fear is unjustified, sorry. \$\endgroup\$ Apr 28 '20 at 12:24

Capacitive touch sensors react to change in capacitance. Pins 1 and 2 , (OSC and VC) on your SGL8022W chip are the ones which define the capacitance change range.

To emulate a touch I would guess you could try following things:

  • Change the values the chip works with on pins 1 or 2 momentarily so that the threshold is triggered with the existing setup.
  • Influence the sensed capacitance on pin 5, TI as to go above/below the trigger threshold momentarily.

Pulse creation:

Now the key is in the word momentary, as you described a pulse of 550ms or less will trigger the "switch".

This you could implement with a 555 Timer circuit configured as a monostable timer where you can define the pulse length.

Logic Level Translating:

  • Open Drain / Open Collector solutions are what I would say are the simplest solution to this.
    • Positive / Negative logic can be obtained by playing with P and N type transitors and combinations.
  • the 555 typically have an open Drain/colector output which will let you create this voltage level translation interface

Circuit influence:

Place a capacitor or resistor in series with a transistor and in parallel with the pin to influence and activating the transistor will allow current to flow through this "momentarily" added circuit to simulate a touch.

Exact values and so on I cannot give you because I do not have the chips or circuit you have , so it will require some measurements and trial and error from you part to see what works.


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