Thank you for reaching out — and your pin reading is actually spot on, which is exactly where most people get confused!
1. Pin-out: on the relay in the kit (Songle SRS-05VDC series), the two pins standing alone at one end are the common (COM) pins — pin 1 and pin 6. They are directly connected to each other inside the relay (the same node brought out on two pins). The other four pins: the middle pair (2 & 5) is the coil, and the pair at the far end (3 & 4) is normally closed (NC) and normally open (NO).
2. What the red jumper does: you’re right that both pin 1 and pin 6 are wired to +5 V in the diagram, and those two pins are internally connected. The key is that the coil’s pin 2 is separately wired to pin 1, so the current path is +5 V → pin 1 (via the red jumper) → pin 2 → coil → pin 5 → transistor → GND — the red jumper is the coil’s +5 V supply. When GPIO17 goes HIGH the transistor conducts, the coil is energized, and the relay “ticks”. You also noticed the diode’s banded (cathode) end on that same line — correct: with pin 2 tied to pin 1 they are one node, and the diode across pins 2–5 is a flyback (protection) diode that absorbs the reverse voltage spike when the coil switches off, protecting the transistor.
The lesson wires it this way for two reasons. First, built-in redundancy: pins 1 and 6 are the same node, so connecting both to +5 V means that even if one jumper works loose on the breadboard, both the coil and the LED still have a complete power path — the experiment stays stable. Second, tidy routing: pin 2 sits right next to pin 1, so a short jumper completes the coil’s supply, while pin 6 down below conveniently feeds the LED circuit (+5 V → COM → NO → LED → resistor → GND), so each circuit picks up its power nearby. Of course, connecting pin 2 straight to +5 V works just as well — both wirings are fine for this lesson.
3. SRS-05VDC-SH vs SRS-05VDC-SL: they are the same Songle SRS sub-miniature SPDT relay family with a 5 V, ~70 Ω coil; the suffix letters are series/variant designations. For this lesson they are equivalent — keep the same wiring and code, no changes needed.
4. “Armature” vs “common”: two names for the same pin. The armature is the moving part of the relay’s contact system, and the terminal connected to it is the common (pole) pin. Some diagrams label it “armature”, others “common”.
We’ve attached a clear schematic along with this reply — it goes well with the explanation above. Please let us know how the build goes — we’re happy to help if anything else comes up!
