ESP32-C3 · Wi-Fi

230 V timer

Shelly 1PM Mini Gen4

DIY · Version 3

Feeder-Relais

The manual — from the bare board to the finished device in its enclosure

Edition 1 · August 2026 · English Hardware v3 · ESPHome firmware · CC BY-NC-SA 4.0

# This is a comment — for explanation only
esphome run firmware/timer-relais-c3.yaml

1What the Feeder-Relais Is

The Feeder-Relais is a DIY control board that switches on a 230 V load at the press of a button for an adjustable time and then switches itself off again automatically. The name comes from its original use case: it replaces the broken timer board of an automatic feeder. Because at its core it just "presses a switch for a certain time," it is suitable for any load you want to switch on a timer.

1.1 What the Device Does

On the front there are three buttons. A short press switches the load on for a stored time:

A small OLED display behind the viewing window shows the Wi-Fi signal at the top, the large clock (set via an internet time server), and the Idle status; at the bottom, the date and free memory. While a timer is running, the seconds countdown is shown in the middle and Feed on the right.

Operation is app-free and cloud-free, via a small, mobile-optimized web page that the ESP32 hosts itself (in the browser at http://feeder-relais.local): trigger timers, adjust times, view network and status values. For connecting to a home automation system (for example ioBroker or Home Assistant), there is also a lightweight JSON interface (Chapter 11).

1.2 The Signal Chain

From the button press to the switched load, the signal passes through five stages. Each has exactly one job:

Button ─►  ESP32-C3  ─►  330 Ω  ─►  PhotoMOS  ─►  Shelly 1PM  ─►  Load
S1–S3      counts the    limits      switches       switches and     (pump,
           time, draws   the LED     galvanically   measures the      feed
           the OLED      current     isolated       230 V load        motor …)

1.3 What Version 3 Does Differently

This manual describes version 3 of the board. Compared to the first version, the design has become considerably simpler:

• The Shelly sits outside the board and is connected via a terminal block (Chapter 13). This keeps the board small and the mains wiring easy to follow.
• All the electronics are on the back of the board. Only the three buttons and the display connector remain on the front — that is, everything that is operated or seen through the front panel.
• The board is four layers with continuous ground planes. This keeps it low-noise and allows a clean separation between mains voltage and low voltage (Chapter 6).
• The enclosure back piece is 3D-printed (Chapter 5) and is deep enough to hold both the board and the Shelly.

2Safety — Please Read First

2.1 The Basic Rules

• All initial function tests of the ESP, buttons, and OLED are carried out exclusively via USB — with no mains voltage whatsoever connected.
• The first 230 V test takes place behind a residual-current device (RCD/PRCD, a "personal protection plug"), with the enclosure closed. Never work inside the open device while it is live.
• A fine fuse (1 A slow-blow) and a varistor belong upstream of the power supply. The small AC/DC modules do not include either of these themselves.
• On the board, a minimum of 6 mm distance (creepage distance) applies between every 230 V line and the low-voltage side. Why, is explained in Section 2.2.
• For the PhotoMOS relay, a type with ≥ 400 V blocking voltage must be used (Chapter 3). An ordinary optocoupler is not permitted here.

2.2 Why 6 Millimeters of Clearance

Between two copper areas on a board, current can not only jump through the air but also creep along the surface — aided by dust, moisture, and dirt. At 230 volts, this "creepage distance" must be large enough. We fix it at 6 mm, which is generous and leaves margin. The only permitted exception is the inside of the PhotoMOS relay itself — this component is the certified isolation barrier and is allowed to carry mains and low voltage within a few millimeters of each other (Chapter 6).

2.3 The Safe Path to First Commissioning

The order in this manual is deliberately chosen so that you do anything dangerous last and can practice safely until then:

1. Assemble the board and flash the ESP without a power supply via USB (Chapters 9 and 10).
2. USB-only test: the buttons, OLED, and the PhotoMOS output are tested completely without mains voltage (Chapter 14).
3. Only once everything works do the power supply and Shelly get added — and the first mains test runs behind an RCD with the enclosure closed (Chapter 14).

3How the System Works

3.1 The Components and Their Jobs

3.2 Why a Shelly — and Why Outside the Board

The Shelly 1PM Mini Gen4 is a ready-made, tested switching relay with power measurement. Using it has three advantages: the risky task of switching the load is handled by a certified, off-the-shelf product; the power is measured (so you can see whether the load is actually running); and the Shelly is itself reachable over Wi-Fi, in case you want to integrate it separately as well.

Our board only "presses the switch" for the Shelly — as a genuine hardware signal, with no Wi-Fi dependency for the core function. In version 3, the Shelly sits outside the board and is connected via a terminal block (Chapter 13). This keeps the board small, the 230 V paths short, and the layout easy to follow.

3.3 What a PhotoMOS Is, and Why This One Specifically

A PhotoMOS is a tiny semiconductor relay. On one side sits an LED, which the ESP drives with 3,3 V. On the other side is a light-controlled switch that is allowed to switch mains voltage. Between them lies only light — that is, a complete galvanic isolation between low voltage and 230 V.

The Shelly's switch input is referenced to mains voltage (it expects a switched L). That's why the PhotoMOS must withstand ≥ 400 V blocking voltage — for example an Omron G3VM-601BY or a Panasonic AQY216.

3.4 Every Component in Detail

Here is the exact function of each component — with the values actually fitted on the v3 board. The reference designators appear this way on the board's silkscreen.

And the terminal blocks at the edge of the board:

4Shopping List: Materials and Tools

Everything you need for one Feeder-Relais. You have the board itself manufactured (Chapter 7); the components are ordered and soldered on (Chapter 9).

4.1 Components on the Board

4.2 Assemblies Outside the Board

• Shelly 1PM Mini Gen4 (type S4SW-001P8EU), max. 8 A / 240 V, dimensions approx. 29 × 34 × 16 mm.
• Mounting material: double-sided VHB tape or a 3D-printed clip to secure the Shelly and power supply inside the enclosure.
• Short wires (e.g. 0,75 mm²) for connecting the board to the Shelly and to the load output.

4.3 Tools

• Soldering iron (temperature-controlled), solder, desoldering braid, flux.
• Fine tweezers, side cutters, wire strippers.
• A USB-C data cable (careful: many cheap cables can only charge!) and a PC.
• Multimeter (continuity and voltage testing).
• A 3D printer for the enclosure back piece (or a print service).
• For the 230 V test: an RCD/PRCD.

5The Enclosure

The enclosure consists of two parts: the front piece (the original front panel with the viewing window and the three button plungers) and the back piece, which you 3D print yourself. The board is screwed to six bosses from behind, and the display sits behind the viewing window.

5.1 Structure: Front and Back Piece

The front piece is the original enclosure's top part. It carries the viewing window (behind which sits the OLED) and the plungers that, when pressed, actuate the three buttons on the board. This is why the position of the buttons is non-negotiable — they must sit exactly under the plungers (Chapter 9).

In version 3, the back piece is deliberately deeper than the original (35 mm instead of the original 5,7 mm), so that the board and the external Shelly fit comfortably inside. A mounting tab with a keyhole slot sits at the top edge for wall mounting.

5.2 Printing the Back Piece Yourself

The template is available as an OpenSCAD file in the project under box/feeder_back.scad. OpenSCAD is a free program that generates a 3D model from a text file — the advantage: all dimensions appear as variables at the very top of the file and can be adjusted.

1. Open OpenSCAD and load box/feeder_back.scad.
2. Press F6 to render the model and save it as a printable file via File → Export → STL. A ready-made STL is already included: box/feeder_back_35mm.stl.
3. Load the STL into your printer's slicer. Recommendation: print with the open side facing up, 3–4 wall lines, 20–30 % infill, no supports needed.

5.3 Height Budget and Mounting

The board is screwed from behind onto the back piece's bosses with six screws (boss grid 45 mm × 70 mm, screw hole 3,2 mm, countersunk for the screw head on the back). Four additional points on the front panel further center the board.

6Understanding the Board

You don't have to design the board yourself — it is finished and ready in the project under kicad-v3/. This chapter explains how it is laid out, so that during assembly and testing you know what belongs where. Anyone who wants to change something themselves will find the KiCad guide in Chapter 8.

6.1 Front and Back

In version 3, all the electronics sit on the back of the board. Only the three buttons and the OLED socket remain on the front (toward the front panel) — everything that is operated or seen.

6.2 Four Layers and the Ground Planes

The board has four copper layers: the two outer layers (front and back) carry the traces, and the two inner layers are continuous ground planes in the low-voltage area. Such ground planes act as a calm reference plane: they keep the design low-noise and the Wi-Fi function stable.

6.3 Mains Voltage Only on the Outside: the 6-Millimeter Rule

The five nets L_IN, L_F, N, SW_SHELLY, and O_LAST carry 230 volts. They are grouped into their own net class "230V" (wider traces, larger clearances) and all sit in the bottom left, well away from the electronics. A design rule encoded in the design requires 6 mm of clearance between every 230 V net and every low-voltage net.

The only exception is the PhotoMOS relay K1: its package is the certified isolation barrier (pins 1/2 = low voltage, pins 3/4 = mains voltage). Only there are the two worlds allowed to meet within a few millimeters — that is exactly what the component is built for.

6.4 The Nets and the Pinout

The following overview shows what each line carries:

The ESP32-C3 uses these pins:

6.5 Every ESP Connection in Exact Detail

This table is the binding alignment between board and firmware. On the left is what the firmware (timer-relais-c3.yaml) does with the pin — with its exact configuration; on the right, where the board routes it. Both sides must match exactly, or the device will not work.

7Getting the Board Manufactured

You don't build a four-layer board at home — you have it manufactured by a PCB fabricator. Today that's cheap and easy: you upload a handful of files and receive the finished boards by mail.

7.1 First, a Test in Plastic

Alternatively (or in addition), print the board outline on paper at 1:1 scale and cut it out.

7.2 Generating Gerber Data

"Gerber" is the standard file format that manufacturers expect boards in — one file per layer, plus the drill data. The finished Gerber files are already included in the project; you can generate them from KiCad like this:

1. Open the project kicad-v3/Timer-Ersatzplatine-v3.kicad_pcb in KiCad.
2. File → Fabrication Outputs → Gerbers — select all standard layers, export.
3. In the same dialog, generate the drill files (Excellon).
4. Pack all generated files into a ZIP archive.

7.3 Ordering from a Manufacturer

Upload the ZIP to a provider such as JLCPCB, PCBWay, or Aisler. Important settings:

8KiCad Step by Step (Only for Your Own Changes)

You only need this chapter if you want to modify the board yourself. If you're just building the existing design, you can skip it — the finished manufacturing data is included. KiCad is a free program for board design (tested with KiCad 8/9/10; menu names may vary slightly).

8.1 Opening the Project and Checking the Schematic

1. Start KiCad and open kicad-v3/Timer-Ersatzplatine-v3.kicad_pro.
2. Start the schematic editor. It shows how all the components are connected.
3. Run Inspect → Electrical Rules Checker (ERC). Warnings about "unconnected power pins" are known and non-critical.

8.2 Footprints and Net Classes

Each component symbol is linked to a footprint — the solder pattern on the board. Under Tools → Assign Footprints, check that, for example, PS1 matches the power supply you actually bought (measure the pin spacing!) and that the PhotoMOS matches the SMD or DIP package.

The net classes are defined in the project file and must not be changed: Default (0,2 mm clearance and trace width) and 230V (1,0 mm clearance and trace width) with the five nets L_IN, L_F, N, SW_SHELLY, O_LAST.

8.3 The 6-Millimeter Rule and the DRC

The creepage-distance rule exists as its own file Timer-Ersatzplatine-v3.kicad_dru in the project. It requires 6 mm between 230 V and low voltage — with the deliberate exception of the PhotoMOS K1:

(version 1)
(rule "230V->SELV 6mm (K1-Barriere ausgenommen)"
   (condition "... 230-V-Netz gegen Nicht-230-V-Netz,
               K1 ausgenommen ...")
   (constraint creepage (min 6mm))
   (constraint clearance (min 6mm)))

After every change, run the DRC (Design Rules Check, Inspect → Design Rules Checker) until it comes back clean.

8.4 Manufacturing Data

Once the DRC and visual inspection (3D view with Alt+3) are clean, export the Gerber and drill data as described in Chapter 7.

9Assembling the Board

"Assembling" means soldering the components onto the board. We go from the flat parts to the tall ones — this way the board always lies stably while you solder.

9.1 Order and Tools

Recommended order: R1 → C2 → PhotoMOS → buttons → OLED socket J4 → C1 → fuse holder F1 → varistor RV1 → terminal blocks. The ESP goes on only once it has been flashed and tested (Chapters 10 and 14).

9.2 The SMD Components

Depending on the type, the PhotoMOS is a small SMD component. Here's how to solder it cleanly:

1. Tin one pad thinly.
2. Place the component with tweezers and solder it to the tinned pad — check its orientation.
3. Solder the remaining pins. Flux helps; use a small amount of solder to avoid bridges.

9.3 The Through-Hole Components and Connectors

• Buttons SW1–3: place them exactly — they must later sit precisely under the front panel's plungers. Press flush onto the board, then solder.
• OLED socket J4: solder the header socket (1×4) so it stands vertically. The OLED is later only plugged on, not soldered.
• Fuse, varistor, terminal blocks: in the 230 V corner, with clearance from the electronics. Solder them properly, with no cold joints.

10Flashing the Firmware

The "firmware" is the program that runs on the ESP. The very first time, it goes onto the chip via a USB cable. All later updates then happen wirelessly (Chapter 15).

10.1 What You Need

• the ESP32-C3 Super Mini (not yet soldered in),
• a USB-C data cable — many cheap cables can only charge; with those the chip is not recognized,
• a PC with Google Chrome or Microsoft Edge (Path B) — or ESPHome installed on the PC (Path A).

10.2 Path A — Using ESPHome

ESPHome is the tool used to build and flash the firmware. A secrets.yaml is not needed — no Wi-Fi data is compiled in.

1. Plug in the ESP via USB-C.
2. Run in the project folder:

   esphome run firmware/timer-relais-c3.yaml

3. ESPHome compiles, asks for the serial port (on Linux, e.g. /dev/ttyACM0; on Windows, a COMx), and flashes.
4. After the restart, the ESP opens its setup hotspot → continue with Chapter 11.

sudo usermod -aG dialout $USER

10.3 Path B — In the Browser

For the ready-made feeder-relais.factory.bin, with no installation at all:

1. Open https://espressif.github.io/esptool-js/ in Chrome/Edge.
2. Plug in the ESP via a USB-C data cable.
3. Leave the baud rate at 115200, click Connect, and select the ESP's serial port.
4. Under Flash Address, enter 0, use Choose File to select feeder-relais.factory.bin, then Program. Wait until "Hard resetting…" appears.
5. Continue with Chapter 11.

10.4 If Flashing Gets Stuck

11Setting Up Wi-Fi and Operating via the Browser

11.1 The Setup Hotspot

The firmware deliberately ships with no Wi-Fi credentials. After flashing, the ESP opens its own hotspot:

1. On your phone/PC, connect to the Wi-Fi network "Feeder-Relais Setup" (password feeder1234).
2. A login window opens (otherwise go to http://192.168.4.1).
3. Select your home Wi-Fi, enter the password, save — the ESP restarts and connects.
4. From now on it's reachable at http://feeder-relais.local.

11.2 The Web Interface

http://feeder-relais.local opens a mobile web app with five tabs:

• Home: three large buttons (trigger T1/T2/T3), a live countdown, and Stop.
• Times: the language selector (German/English/French) at the top, below it the three timer durations (1–600 s), stored permanently.
• Network: Wi-Fi, IP mode DHCP/static, NTP server, hostname, Wi-Fi roaming, restart (Chapter 12).
• Status: version, uptime, free memory, Wi-Fi with signal bars, IP/MAC, reset reason, relay state.
• Service: live log, firmware update, and restart (Chapter 15).

11.3 The Status Traffic Light and the JSON Interface

The header shows a status dot: green = everything OK, yellow = a timer is running, red = a fault while idle (e.g. OLED unreachable or no Wi-Fi). The same traffic light is shown on the device by the dimmed onboard RGB LED.

For home automation, the ESP offers a JSON interface. The most important endpoints:

12Network, Language, and Display

12.1 Network Settings

In the Network tab you can set:

• IP mode: DHCP (default) or static (with IP/gateway/mask/DNS). The static IP is applied on the next connection and is active after a restart.
• NTP server: the time server used to set the clock (default de.pool.ntp.org).
• Hostname: the name on the network (default feeder-relais). It is changed at runtime — the …​.local address takes effect immediately.

12.2 Wi-Fi Roaming

The Wi-Fi roaming (802.11k/v) switch only makes sense if you have multiple access points with the same SSID (mesh/UniFi) that support the technology. In that case, the device can actively switch to the stronger access point. Default: off. After toggling it, the "Reconnect now" button helps it take effect immediately.

12.3 Operating the Buttons and OLED

On the device, the buttons are labeled: S1 = Down/Manual, S2 = SET, S3 = UP.

• short press S1 / S2 / S3 → triggers timer 1 / 2 / 3 with its configured time.
• long press UP (S3) ≥ 1,2 s → stops all timers, switches off.
• long press SET (S2) ≥ 3 s → opens an info menu (view-only: Wi-Fi, IP, time, system). S1/S3 scroll, short SET closes it.

The OLED (128 × 32) shows the Wi-Fi bar at the top, the large clock or countdown, and the status (Idle/Feed); at the bottom, the date and free memory. Weekday, status, and menu titles follow the configured language. Until the first time synchronization, it shows "--:--".

13Connecting the External Shelly

13.1 Wiring

The Shelly has four terminals: L, N, SW (switch input), and O (load output). Four short wires connect it to the board's terminal block J1:

The Shelly is secured lying flat inside the enclosure (VHB tape or a clip). Keep the wires short and the screw terminals tight — no exposed copper may be visible.

13.2 Setting Up the Shelly (Input Mode)

After the first power-on, you set up the Shelly once (via its own app or web interface):

1. Connect the Shelly to Wi-Fi (per the Shelly's instructions).
2. Set Input Mode = Switch (Follow) — this makes the relay follow the SW signal exactly.
3. Done: from now on, the ESP determines how long the load runs, via the PhotoMOS.

14Assembly and Commissioning

14.1 Assembling and Preparing the ESP

The small parts are soldered (Chapter 9). Now the ESP:

1. Flash the ESP via USB and test the Wi-Fi connection (Chapters 10 and 11) — this is easiest before it is soldered in.
2. Solder the ESP onto the board (pin headers or directly).

14.2 The USB-Only Test

14.3 The First Mains Test

1. Visual inspection: no solder bridges, no short circuit between L/N, ≥ 6 mm clearance everywhere between 230 V and low voltage.
2. Solder in the power supply, connect the Shelly (Chapter 13), wire up the load.
3. Close the enclosure.
4. Switch on via an RCD/PRCD. The OLED shows the clock/status.
5. Set up the Shelly (Input Mode "Switch"), then run a button test with the load.
6. Set the times as desired via http://feeder-relais.local.

15Firmware Updates and Maintenance

15.1 Wireless Updates (OTA)

After the initial USB flash, two wireless update paths are set up — the USB port is welcome to be hard to reach once the device is installed:

• Network OTA: esphome run firmware/timer-relais-c3.yaml updates over Wi-Fi.
• Web upload: in the Service tab, upload feeder-relais.ota.bin. The device then restarts.

15.2 The Service Log

With live view enabled, the Service tab shows the most recent log lines, filtered by level (ERROR/WARN/INFO/DEBUG). This helps with troubleshooting without having to hook the ESP up to a cable. Full logs are also available via esphome logs firmware/timer-relais-c3.yaml.

16Troubleshooting

16.1 While Flashing and Connecting

16.2 During Operation

17Appendix: Pinouts, Files, Glossary

17.1 Pinout and Net List

The five 230 V nets (net class "230V"): L_IN, L_F, N, SW_SHELLY, O_LAST.

17.2 Project Files

17.3 Glossary

17.4 License and Thanks

This manual is licensed under CC BY-NC-SA 4.0. Its structure follows the documentation rulebook of the sister project AskSin-Analyzer: a table of contents with jump targets, fixed page-break rules, and the footer with the way back to the contents on every page.

Building this project is at your own risk. 230 volts can be fatal — when in doubt, consult a qualified electrician.