February 2021

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I’m rolling my own home security system for pennies on the dollar (and lots and lots of time, but this kind of stuff is fun to me). Here’s what I ended up with for the kitchen. It controls three distinct lighting zones and three entry points (two doors and one window). It has its own captive portal for network/LED/sensor configuration (using Autoconnect) and it’s fully connected. So far it’s testing out pretty well. Here are the notable parts:

  1. ESP-12F ($1.09 from Aliexpress). This is the brain — the venerable ESP8266 module, with some custom code to control the lights, sensors, and communications. I used pins 5, 4, and 15 (with a 10K to ground) as PWM outputs, and pins 12, 13, and 14 as inputs. I broke out pins EN and 0, as well as VCC and GND and soldered up the wires so I could re-insert it into the programmer in case the OTA updates failed.
  1. Cat-5E network cable (free, on hand). I use this stuff a lot. I used all eight wires in the cable, plus a couple more for VCC and GND.
  2. Resistor Header (a couple cents). I broke out EN and pin 0 so I could place 10K resistors and remove them again if necessary to program.
  3. Dual MOSFET Trigger ($0.84 at Aliexpress). This triggers with 3.3V and drives up to 36V, 400W — plenty for each of my three 12V LED lighting zones. There’s one of these per output channel. The one on pin 15 also contains a 10K resister to ground, which is necessary for normal operation.
  4. Mini DC Step-down Buck Converter, 3A ($0.50 on eBay). This takes the power from the 12V LED power supply and efficiently converts it down to the ~3.3V operating voltage of the ESP-12F. I originally planned on using a linear regulator thinking that this might cause some interference with the ESP, but that turned out to not be a problem. (The AMS 1117 regulator would have probably run hot, but not too hot.)
  5. Power (free, on hand). This connects to the 12V power supply. I used green for 12V because that’s what I had on hand.
  6. Input Sensor Header (free, on hand). This breaks out the three input pins in a 2×3 header, once side of which is all GND.
  7. Output Header (free, on hand). This breaks out the three output pins in a 2×3 header, once side of which is all GND.
  8. Removable 10K resistor (pennies). The third output channel MOSFET driver has this resistor soldered on, but it basically takes pin 15 low, which is required for normal operation.

Here’s how I planned out the wiring and headers: