RL-01Open Source Hardwaredesigned
4-Channel Relay Board
Opto-isolated 4-channel SPST/SPDT relay board for switching mains AC or DC loads. PC817 → AO3400A → Songle SRD-05V relay per channel.
Readout
Board80×65mm
Layers2layer
Components17rows·17parts
BOM Cost$2.93/ unit
Placementextracted
DRC0S/0U·1v
Schematics1sheets
Info
An opto-isolated 4-channel relay board for switching anything from mains AC to a 12V solenoid. Each channel: GPIO → 330R → PC817 LED → opto-isolated → AO3400A FET → relay coil → 1N4007 flyback. Screw terminal on the contact side breaks out COM, NO, NC.
Currently the TOML wires up 2 channels (U1/Q1/K1/J3 and U2/Q2/K2/J4); adding the other two is a copy-paste of the same per-channel block.
Specification
| Channels | CH-01 4 (currently 2 implemented) | Channels 3-4 placeholder; expand circuit TOML to add U3/Q3/K3/J5 etc. |
| Isolation | IS-01 PC817 optocoupler per channel | Logic GND fully isolated from relay-coil GND |
| Driver | DR-01 AO3400A low-side N-MOSFET | 1N4007 flyback diode across each coil |
| Relay | RL-01 Songle SRD-05VDC-SL-C SPDT | 10A/250VAC, 5V coil, common THT relay |
| Outputs | OT-01 3-pin screw terminal (COM/NO/NC) per channel | Phoenix MPT 0.5/3-2.54 |
| Board | PB-01 2-layer, 80 × 65 mm | 20 components for 2 channels (~40 for full 4-ch) |
Architecture
Features
RL-F1
Real isolation
Each channel has a PC817 optocoupler. Logic and relay coil grounds are independent — drive directly from a 3V3 MCU GPIO without ground loops.
RL-F2
Switches mains AC
10A/250VAC relay contacts. Wire mains hot through COM/NO with proper creepage spacing on the through-hole side.
RL-F3
Repeats per channel
Each channel = 1 opto + 1 FET + 1 relay + 1 flyback + 2 resistors + 1 terminal. Add channels by repeating in the TOML.
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Bill of Materials
17 rows priced live from JLCPCB · refreshed 2026-04-27
17 rows
· 17 components
· Total $2.93
Hover row → component highlights on board
| Ref | Category | MPN | Description | Qty | Unit | Ext | Stock | Links |
|---|---|---|---|---|---|---|---|---|
| J1 | PinHeader_1x06 | PinHeader_1x06_2.54mm | 1x6 0.1in pin header | 1 | $0.15 | $0.15 | — | LCSC |
| J2 | Phoenix_MPT_2P | MPT 0.5/2-2.54 | 2-pin 2.54mm screw terminal | 1 | $0.45 | $0.45 | — | LCSC |
| J3 | Phoenix_MPT_3P | MPT 0.5/3-2.54 | 3-pin 2.54mm screw terminal | 1 | $0.65 | $0.65 | — | LCSC |
| J4 | Phoenix_MPT_3P | MPT 0.5/3-2.54 | 3-pin 2.54mm screw terminal | 1 | $0.65 | $0.65 | — | LCSC |
| U1 | DIP-4 | PC817X2NIP0F | Phototransistor optocoupler | 1 | $0.20 | $0.20 | — | LCSC |
| U2 | DIP-4 | PC817X2NIP0F | Phototransistor optocoupler | 1 | $0.20 | $0.20 | — | LCSC |
| Q1 | SOT-23 | AO3400A B | N-channel MOSFET 30V 5.8A | 1 | $0.05 | $0.05 | In stock | LCSC |
| Q2 | SOT-23 | AO3400A B | N-channel MOSFET 30V 5.8A | 1 | $0.05 | $0.05 | In stock | LCSC |
| K1 | Songle SRD | SRD-05VDC-SL-C | SPDT 10A 250VAC relay | 1 | $0.20 | $0.20 | In stock | LCSC |
| K2 | Songle SRD | SRD-05VDC-SL-C | SPDT 10A 250VAC relay | 1 | $0.20 | $0.20 | In stock | LCSC |
| D1 | SMA | 1N4007 | 1A 1000V flyback diode | 1 | $0.0062 | $0.0062 | In stock | LCSC |
| D2 | SMA | 1N4007 | 1A 1000V flyback diode | 1 | $0.0062 | $0.0062 | In stock | LCSC |
| R1 | R_0402 | RC0402FR-07330RL | 330R 0402 1% (opto LED) | 1 | $0.0004 | $0.0004 | In stock | LCSC |
| R2 | R_0402 | RC0402FR-0710KL | 10k 0402 1% (gate pull-down) | 1 | $0.0004 | $0.0004 | In stock | LCSC |
| R3 | R_0402 | RC0402FR-07330RL | 330R 0402 1% (opto LED) | 1 | $0.0004 | $0.0004 | In stock | LCSC |
| R4 | R_0402 | RC0402FR-0710KL | 10k 0402 1% (gate pull-down) | 1 | $0.0004 | $0.0004 | In stock | LCSC |
| C1 | Radial THT | EEU-FR1A101 | 100uF 10V radial electrolytic | 1 | $0.10 | $0.10 | — | LCSC |
| Total | $2.93 | |||||||
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Wiring
Real KiCad schematic auto-generated from the designgraph TOML.
1 sheet · click to open
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Mech
2-layer, 80 × 65 mm. Through-hole relays + screw terminals dominate the footprint. Auto-routed by Rust pipeline.
80 × 65 mm 2 layer
RL-01 Front
RL-01 Back
DRC Report
2026-05-05T18:13:51
0
Shorts
0
Unconnected
0
Parity
1
Violations
Violations by type
1×
copper_edge_clearance
Board edge clearance violation (board setup constraints edge clearance 0.5000 mm; actual 0.4500 mm)
Component Map · Dimensions
Hover BOM ↔ Map
Ready
Industrial-style box with M3 standoffs at all four corners. Phoenix terminals exit the long edges; logic header pokes through the top. Lid clears the SRD relays (~16mm) with 6mm of headroom.
3D Model
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RL-01 Copper Layers
X-Ray Layer Viewer
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Instructions
Not yet populated for this project.
→ Roadmap item INST-01: assembly guide authoring.
→ Roadmap item INST-01: assembly guide authoring.