Pinout
Relay module (1-channel SRD-05VDC, SPDT) pinout
Pins
- NO — normally open contact (closes when the relay is energized)
- COM — relay common contact
- NC — normally closed contact (opens when energized)
- IN (trigger — active-low on most of these boards: LOW energizes the relay)
- GND (logic side)
- VCC (logic side, 5V typical)
Specifications
| Relay | SRD-05VDC-SL-C |
|---|---|
| Coil voltage | 5 V DC |
| Coil resistance | 70 Ω |
| Coil current | ≈71 mA (0.36 W) |
| Pick-up voltage | ≤ 3.75 V (75 % of rated) |
| Contact form | SPDT (1 Form C): COM, NO, NC |
| Contact rating | 10 A 250 V AC / 10 A 30 V DC (resistive) |
| Operate / release time | ≤ 10 ms / ≤ 5 ms |
| Trigger input | Active-low on most boards (check jumper/silkscreen) |
| Logic supply | 5 V |
Notes
- IN itself draws almost nothing — the module’s own onboard transistor does the real work of switching the coil, drawing it from VCC. That coil current is real, though: a common 5V relay (the SRD-05VDC-SL-C on most of these boards) draws roughly 70mA per relay while energized, so a 4- or 8-relay board with every channel on at once can be pulling several hundred mA from VCC — enough to matter if VCC is a microcontroller’s own 5V pin.
- The switched side (COM/NO/NC) is a completely separate current budget from the coil above — it is electrically isolated and typically rated up to 10A, set by the relay’s own contact rating and whatever supply is wired through it, not by anything on the logic side.
