uBer Switch

Full schematic — uBer Switch V1.1 (TH Custom Effects, 09/2014).

Architecture

The board has three functional regions: the microcontroller and its 5 V supply (REG1, IC2, C2, C3); the relay drive (Q1, R1, R3, K1, D1, plus the status LED and R2); and the audio-side mute (the SMD optocoupler OC1, which sits on the back of the PCB). The audio signal itself never touches the digital side — it goes through the relay contacts only.

Switching sequence — the mute-while-switch trick

Each press of the momentary footswitch (S1) generates an interrupt at the microcontroller. The PIC then runs this short sequence:

1. Activate the optocoupler (via Q1, driven by the PIC's GP1 / GP2 pins through R1 and R3). The OC1 output transistor turns on, shorting the audio signal at TP2 to A_GND. The output is now silent.
2. Wait a few ms for the audio to settle.
3. Toggle the relay coil — current through K1's coil energises or de-energises depending on the previous state. The contacts switch.
4. Wait a few more ms for the contact bounce to settle.
5. Release the optocoupler — the audio path is restored, with no switching transient since the signal was already muted before the relay moved.

Total transition: under 10 ms typically. Inaudible — no popping, no clicking, just a clean state change.

The relay: K1 (FTR-B3CA-4.5Z)

This is a subminiature DPDT signal relay with a 4.5 V coil. One pole switches the input side (connecting A_IN to either A_TO or A_OUT depending on state); the other pole switches the output side (connecting A_OUT to either A_FRM or directly back to A_IN). When energised, the relay routes signal through the effect (A_IN → A_TO → ... → A_FRM → A_OUT); when de-energised, it bypasses (A_IN → A_OUT directly). D1 (1N5817 Schottky) is the standard flyback diode across the coil — it absorbs the inductive kick when the relay turns off, protecting Q1's collector from the voltage spike.

The optocoupler: OC1 (CPC1017NTR, SMD on back side)

The OC1 is a small surface-mount optocoupler on the back of the PCB. Its input side (LED) is driven from the digital domain by Q1; its output side (a small MOSFET) sits across the audio signal at TP2 and shorts it to A_GND when activated. The galvanic isolation matters because the digital side has noisy, fast-edged switching transients (driven by the PIC's GPIO pins); without isolation those transients would couple into the audio ground and you'd hear them. The optocoupler breaks that path completely.

The microcontroller: IC2 (PIC10F202)

A small PIC10F202 in DIP-8 — pre-programmed with the switching firmware. The PIC handles: footswitch debouncing (S1 input), state tracking (engaged or bypassed), the mute-while-switch sequence above, the LED status output, and the radiobutton bus protocol on the RELEASE pads. The chip ships pre-flashed; nothing needs to be programmed by the user.

Power supply

9 V DC enters at the +9V pad. REG1 (78L05) drops it to a stable +5 V (called VD internally) for the PIC and the relay coil. C2 (100 µF) is the main 5 V rail filter; C3 (100 n MLCC) is the local bypass at the PIC's VDD pin. This board has no reverse-polarity protection — the audio effect downstream of it should provide that, since the uBer Switch usually shares supply with whatever it's switching.

The board has eleven labelled pads grouped on its two long edges. The right side carries the audio-side connections (all prefixed A_); the left side carries the control-side connections (footswitch, RELEASE bus, power, digital ground).

Pad labels — silkscreen on the actual PCB matches what you see here.

Audio-side pads (right edge)

In bypass mode the relay routes A_IN → A_OUT directly (the effect is skipped). In active mode the relay routes A_IN → A_TO (into the effect) and A_FRM → A_OUT (out of the effect, back to the chain).

Control-side pads (left edge)

Grounding — A_GND vs GND

This is the most important grounding decision in the build. The board has two ground nodes:

• GND — the digital ground. The 9 V supply return, the PIC's VSS pin, the relay coil's return, the optocoupler input's cathode.
• A_GND — the analog ground. The audio-side reference for the input/output sleeves and the optocoupler's output side.

The two grounds need to be connected somewhere for the circuit to function — they're not floating. The default V1.1 behaviour is to bridge them on the PCB itself, by a short trace on the back side. This is convenient for simple builds: just wire your jack sleeves to either pad and the supply ground to GND, and everything works.

For more sensitive builds — particularly large multi-effect boards where star-grounding helps — you can break the on-board A_GND/GND trace and route the analog and digital ground returns separately, joining them only at the chassis or at the input jack sleeve. To break the connection: look at the back side of the PCB, find the small bridge near the LED-end of the board, and cut it with a sharp knife. To restore later: just bridge the same two pads with a blob of solder.

Back side of the PCB. The OC1 footprint (top centre) is where the SMD optocoupler is soldered. The A_GND ↔ GND bridge is the small short trace near the bottom edge that can be cut for star grounding.

This is a small build — three resistors, two caps, one transistor, three other components. The kit ships pre-programmed PIC.

The trickiest step is the SMD optocoupler on the back side — that goes first, before the through-hole parts. Once that's done the rest is conventional through-hole assembly.

SMD optocoupler (OC1) — back side

This is the only SMD step. Flip the PCB to its back side. Find the OC1 footprint (silkscreen labelled). The technique:

1. Pre-solder one pad first. Apply a small dot of solder to one of the four pads — pick the pin-1 corner if you can identify it from the silkscreen.
2. Locate pin 1. The CPC1017NTR has a small dot or indent at pin 1; the silkscreen shows a matching dot. Match them up.
3. Place the package centred over the four pads. Make sure all four pins are sitting on copper.
4. Apply pressure with tweezers to hold the part down, then re-flow the pre-soldered pad with the iron — this tacks the part in place.
5. Solder the remaining three pads using a fine-tip iron and thin solder.

CPC1017N SMD optocoupler in place on the PCB back side. The "CPC1017N" marking on the package faces up; the dot on pin 1 matches the silkscreen dot.

Resistors and diodes

Flip back to the top side. All three resistors — metal film, ¼ W. R1 (1k), R2 / CLR (2k2), R3 (2k2). The colour-band column in the BOM helps verify each. Then fit D1 (1N5817 Schottky) — polarity matters; band toward the relay-coil + side per the silkscreen.

IC socket and relay

Fit a DIP-8 socket for IC2 (the pre-programmed PIC10F202). Don't insert the chip yet — match the notch on the socket to the silkscreen. Then solder the K1 relay (FTR-B3CA-4.5Z) directly — the relay's white plastic body has a marking indicating pin 1; match the silkscreen orientation. Eight pins total.

Transistor and regulator

If you want to socket Q1, do it now (single-row 3-pin socket). Q1 = BC549 (NPN): pinout C–B–E (flat side facing you, leads down) — match the flat side to the silkscreen flat. REG1 = 78L05 in TO-92 — pinout varies by manufacturer, verify against your specific 78L05 datasheet before soldering. Wrong orientation may damage the regulator on first power-up.

MLCC and electrolytic capacitors

Fit C3 (100 n MLCC) first — non-polarised, no orientation. Then C2 (100 µF / 6.3 V electrolytic). C2 has limited height and width on the PCB footprint — pick a low-profile, narrow can to fit cleanly. Polarised — long lead is positive; match (+) on the silkscreen.

Off-board connections (LED, footswitch, pads)

Solder wires or pin headers for the LED (anode = long leg = pad marked + on silkscreen), the footswitch (SW_A-1 and SW_A-2), and the audio + power pads on each edge. Standard wire-soldering — strain-relieve where helpful by passing wires through the PCB if room allows.

Insert the PIC

Insert IC2 (PIC10F202, pre-programmed) into the socket. Match the notch. The PIC ships ready to go — no programming needed.

Mounting in the enclosure

The PCB is small enough to mount directly to the back of the momentary footswitch using double-sided tape. This keeps the wiring runs short and the assembly compact — typical use case is to fit it inside an existing 1590B-class effect enclosure with the footswitch at the bottom.

Single uBer Switch wiring

For a standalone build (one uBer Switch in front of one effect), the wiring is straightforward — the audio path uses A_IN, A_TO, A_FRM, A_OUT plus a ground tie; the control side uses the footswitch and 9 V power. Leave the RELEASE pads unconnected.

Two-board radiobutton chain

Daisy-chaining the RELEASE pads between boards activates the radiobutton feature: pressing the switch on one uBer Switch automatically deactivates any other uBer Switch on the same chain. Useful for amp-channel selectors and parallel effect-loop arrangements where you want only one of several effects active at a time.

Two uBer Switches sharing a single effect loop, with the RELEASE pads daisy-chained for radiobutton operation. Each board has its own LED and momentary footswitch; both share the audio jacks and the +9 V supply. Pressing either switch automatically releases the other.

Daisy-chain mechanics

Chain 3 or more uBer Switches by connecting all their RELEASE pads together (one common bus wire passing through every board). The PIC firmware on each board listens to that bus — when any one PIC fires the "I'm engaging" signal onto the bus, the others see it and disengage their own relays. The result: at any moment, exactly zero or one of the chained uBer Switches is engaged.

Star-grounding option (if needed)

For complex multi-effect builds where ground noise becomes a problem, you can break the on-board A_GND ↔ GND bridge (see §03) and route the two grounds back to your central star-ground point separately. This is rarely necessary for simpler builds — try the default configuration first; only break the bridge if you can hear digital noise leaking into the audio path.

Final note

The uBer Switch will make any effect you put behind it absolutely silent on engage / bypass. That's the whole point.