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I have a lot of LED flashlights and lanterns from China that use a simple IC as their driver to get these different light modes. For instance I have this small keyfob lamp that lights in the following modes when the momentary tactile button is pressed - (High mode -> Low mode -> Blinking Mode -> Off), and yes I have to cycle through all modes to turn it off. Additionally long pressing the button will make it go into an SOS flasher mode.

I opened up the lamp and took a close look and found there only a total of 4 components, the LED, a momentary switch, a 3R0 SMD resistor and finally a SOT23-6 type IC with “2819” written on it. I googled for that IC and found it’s FM2819 by “Shenzhen Fuman Elec” and found its datasheet too. The circuit used in the lamp is exactly the same as the one shown in the datasheet.

What I want to know is that is there any way of modifying the circuit/wiring to get rid of all these light modes? since all I want is just plain ‘ON’ and ‘OFF’.

  • SW in the circuit is for switch.

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3 Answers 3

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Your S1 is almost certainly not an closing switch,

schematic

simulate this circuit – Schematic created using CircuitLab

but a momentary pushbutton,

schematic

simulate this circuit

considering it's used to cycle through modes.

This sounds very much like

Throw away existing circuit, replace S1 by toggling button, be done.

Alternatively, you could also

Throw away existing circuit, replace with circuit that toggles output based on push button.

But that'll require a couple more components (two transistors for toggling, plus a bit of capacitance for de-ringing the pushbutton) or a small microcontroller (e.g. an Attiny8).

Modification of the existing circuit is not really an option – it's almost certain that the IC is single-purpose; I can't read the datasheet in Chinese, but seeing that it's only 2 pages in length, it's certainly not a programmable controller.

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  • \$\begingroup\$ The circuit board is really small, so is the enclosure. If I have to use a toggle/latching switch then it must the same size of that momentary button, which is 5mm*5mm. I don’t think latching switches come in that size. \$\endgroup\$
    – Kokachi
    Commented Mar 15, 2020 at 19:34
  • \$\begingroup\$ You are right about the button diagram. Will 2 additional transistors and a capacitor replace this circuit? \$\endgroup\$
    – Kokachi
    Commented Mar 15, 2020 at 19:40
  • \$\begingroup\$ ... together with at least two resistors, yes, you can make a latch from two transistors. probably larger than an Attiny8. \$\endgroup\$ Commented Mar 15, 2020 at 19:43
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    \$\begingroup\$ The IC provides more than just the light mode, from an translation it does current limiting, pwm, and other functions, based on R. Replacing it with a single switch would likely poof the led. \$\endgroup\$
    – Passerby
    Commented Mar 15, 2020 at 19:58
  • \$\begingroup\$ @Passerby won’t the smd resistor do the trick for current limiting? \$\endgroup\$
    – Kokachi
    Commented Mar 15, 2020 at 20:04
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Also, for lanterns, I can advice module, that I use by my self. With capacitor sensor.

Simple and cheap ttp223, you can set up output "polarity", and trigger action (latching) by fuses. just add some MOSFET and few resistors. https://vi.aliexpress.com/item/32957041799.html

And "powerful" OE-TP module, based on SGL8022W IC. It can be configurated as dimmer regulator, or "sharp" on\off switch. https://vi.aliexpress.com/item/32974849050.html

P.S. Capacity sensor is great decision, but it can indecently triggered by water or pets. P.P.S. Also you can look on E-cigarette flow sensor...

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Yes, I search same information, and find. Just on\off IC. YUSIJIE-LSM01 YUSIJIE-LM01

https://www.alibaba.com/product-detail/YUSIJIE-LM01-LED-control-chip-Trigger_62490420642.html (video present)

And very possible it used in this China modules... https://vi.aliexpress.com/item/1005002730537353.html

With hall-sensor CC6201ST https://datasheet.lcsc.com/lcsc/1811061532_Cross-chip-CC6201ST_C285995.pdf

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  • \$\begingroup\$ That chip is not "just on/off", it is On-Flash-Off. \$\endgroup\$
    – Maple
    Commented Aug 8, 2023 at 22:21
  • \$\begingroup\$ Oh! my mistake.... on\off model is YUSIJIE-LM01 alibaba.com/product-detail/… \$\endgroup\$
    – andrew
    Commented Aug 8, 2023 at 22:37
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    \$\begingroup\$ While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. - From Review \$\endgroup\$ Commented Aug 9, 2023 at 0:04

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