Suggesting the use of a level-shifting buffer in the wiring

[eikehein]

Hey,

This is such a cool little project, thanks for sharing it with the world.

However, it suffers from an issue that many of the documented OBEGRÄNSAD hacks do: It connects the 3.3v logic pins of the esp32 directly to the SCT2024 drivers in the lamp, even though the drivers are run at 5v and the data sheet says that VIH is then at 3.5v (0.7x5V).

For sure this works for many people, but it's technically outside spec and has no reliability margin. It can very well also not work.

I recommend adding the suggestion to use a simple buffer to the shift up to 5v to the README, e.g. SN74HCT125N. They're ubiquitous, you can also easily get them on bread-boardable breakout boards for the soldering-disinclined and they are easy to hook up.

Bonus: Your project is a fantastic entry-level project for beginners, and this as good an opportunity as any to gently teach folks about mixing logic voltage levels and using shifters.

[BrookeDot]

What do you think about something like the BSS138?

• https://www.adafruit.com/product/757
• https://www.sparkfun.com/sparkfun-logic-level-converter-bi-directional.html

[Solmath]

I'm getting a PR ready with some additional recommendations for the wiring: https://github.com/Solmath/ikea-led-obegraensad/tree/feature/electrical-wiring-documentation

Now I noticed, that we have five signal lines (including the button), but the suggested converters only have four channels. Personally I don't really need the button, so I'll probably just leave it disconnected. Another solution could be to connect the button to a 5V tolerant input pin if such a pin is available. This should also be pointed out in the documentation.

[c64emulator]

1. Why use a level-shifter for interfacing the MCU with the SCT2024?
   The SCT2024 can be operated with an VDD from 3V to 5.5V, high level (VIH) is detected at 0.7 * VDD (for Recommended Operating Conditions of the SCT2024 see datasheet at <http://www.starchips.com.tw/pdf/sct2024/>).
   To perfom the level shift, a very simple method is suggested in <https://hackaday.com/2017/01/20/cheating-at-5v-ws2812-control-to-use-a-3-3v-data-line> : A signal diode is placed in series with the power supply of the panel. This drops the VDD of the SCT2024 to 4.3 V, which means a (0.7 * 4.3V =) 3.01 V signal can be used to control it. A drawback may be a degression of the brightness of the LED on the same power supply (which should be still fine for indoor use).
2. Why use a level-shifter for a dump hardware part like a button?
   The button is connected to a GPIO of the MCU and to GND on the other side. From software side the button events are handled by BfButton class (see description at <https://github.com/mickey9801/ButtonFever>. The button object is created by:
   BfButton btn(button_mode_t mode, uint8_t pin, bool pullup=true, uint8_t buttonLogic=LOW);
   The third parameter means: Use internal pullup of the GPIO.
   IMHO, there is no level-shifting needed for reading button events on input pin of a ESP.
   For more details see a tutorial about using buttons in ESP32 projects at <https://esp32io.com/tutorials/esp32-button>.

JM2C.