Soemarko Ridwan

iOS & Web Developer ⟡ Coffee Addict ⟡ Scuba Diver

Project Katara - Build Log 6: Build Guide

Pictured is my simplified (read: sad attempt at) drawing the whole wiring diagram. The wiring is relatively simple. Just make sure you solder it nice and tidy, and crimp things tight.


  • ESP32 dev board — $5
  • 0.96” OLED — $5
  • R10 800 L/h aquarium pump — $5
  • KY-040 rotary encoder module — $0.50
  • Switch with LED — $1
  • IEC320 C14 Male Socket with fuse and switch — $1
  • AC to DC 5V 3.6A — $5? (I found this around the house)
  • Waterproofed DS18B20 — $1
  • Water heating element. Choose carefully — $13
  • Good Solid State Relay — $20
  • Total: $56.50 + wires, screws, connectors, etc.
  • Plus a pair of M7 nut and bolt, and a bunch of M3s screws

As you can see, the water pump is controlled directly by the switch and completely skip the ESP. I don’t find it necessary to have it controlled by ESP. I’ll need a button to control it anyway. It is simpler this way.

I have an LED indicator that shows when the water heater is on. I put it in as the same pin as the internal LED pin so it’ll blinks when updating the firmware via OTA. And for simplification, I just get a switch with LED in it. Less things to mount. My pinouts are:

  • DS18B20 — D27
  • OLED — D21 (sda), D22 (scl)
  • KY040 Encoder — D32(clk), D34(sw), D35(dt)
  • SSR — D23
  • LED — D2 (same as the ESP32 dev internal LED).

Use the exact pins and you can just upload the firmware as is. Remember to upload it to you ESP at least once (. And you can connect it to your home wifi and use the OTA update.

Thingiverse & GitHub

Print the things. I highly recommend a 1mm nozzle to speed things up. These are mostly square shaped. Support is not needed, and it should be obvious where the print orientations are (hint: just select the largest flat surface as bottom).

I’ve left the centre blank so you can design your own mounting points / holes.

Putting it together is easy. First do the centre, mount everything inside. Next screw bottom to centre with a transparency plastic in between. Then mount the water heater, pump and DS18B20 to bottom. Clamp both things together.

Plug everything from top, and snap it shut. And you’re done. Get a container / a bucket. Clamp it to a side. Pour water. Plug it in. Turn it on. Turn pump on. Start PID.


Also configure WiFi, the default SSID is the one with “SV-“ prefix. default password is “SousVide” (note the case). Click “Configure new AP” to assign the ESP to your home WiFi.

Then configure Blynk if you like. Start from the app, you’ll need the auth code first. At the minimum you’ll need 800 energy. Graph (super chart) +900, another label for ESP temp +400, and heater LED indicator +100. Definitely not enough for everything without paying for more energy. But the graph is not necessary, and you can just use the “Value Display” instead to save some energy. Or self host blynk server for unlimited energy.

Next will be the final post, the official release of Katara: Open Source Sous Vide Cooker. Yeah, I kinda married to the name.