Overview & Features
The Effect-Control V1.2e is the next step beyond the classic Ultimate Switch. It is a complete five-channel relay loop switcher driven by a PIC microcontroller, designed to be the brain of a multi-effect build inside a single enclosure. Each channel is an independent true-bypass relay loop with its own indicator LED and footswitch input. The PIC firmware decides which relays are active based on a configurable operating mode.
Assembled Effect-Control prototype — five FTR-B3 relays, PIC microcontroller, 7805 regulator, and onboard mute optocoupler
Four operating modes
Mode 1 — Standard
Each channel toggles independently on/off. Press SW_n, channel n flips state. Up to five channels active at once in any combination.
Mode 2 — True Radiobutton
Exactly one channel active at any time. Pressing a switch enables that channel and disables the others. No "all off" state.
Mode 3 — Fake Radiobutton
Like Mode 2, but the active channel can be toggled off — pressing the same switch a second time mutes the unit (all relays bypassed).
Mode 4 — Rotary / Cycle
Cycle up and/or down through the active channels using one or two momentary switches. Number of active loops set on JP1.
Circuit Theory
Effect-Control V1.2 schematic — PIC controller, five identical relay channels, 7805 power, optocoupler mute
The signal path of the Effect-Control is purely passive. Each channel is a single FTR-B3CA-4.5Z relay that either bridges FROM_BOARD to TO_BOARD directly (effect bypassed) or routes the signal out through the EFF connector and back in from the wired-in effect (effect engaged). All five channels share a common signal bus, so any combination can be active simultaneously without summing — the relays simply wire each effect into the chain when armed.
The control side is digital. The PIC16LF1826/27P (IC4) reads the six footswitch inputs (SW_1…SW_6) and the four mode/loop-count jumpers on JP1, runs the firmware state machine, and drives five general-purpose I/O pins to the relay drivers. R1 and R2 (100k) form the reset/MCLR network for the PIC. C3 (100n) decouples the digital supply at the chip pins.
Relay driver stage (×5 identical)
Each of the five channels uses an identical low-side BJT driver. The PIC output drives the base of a 2N5088 NPN transistor (Q1–Q5) through a 1k base resistor (R3–R7). When the PIC pin goes high, the transistor saturates and pulls the relay coil's low side to ground; the high side is permanently tied to the VA rail. A 1N5817 Schottky flyback diode (D2, D4, D6, D8, D10) across each coil clamps the inductive kick when the relay drops out, protecting the transistor from reverse-voltage spikes.
In parallel with the relay-coil branch, an indicator LED (D1, D3, D5, D7, D9) fires through a 1k current-limit resistor (CLR1–CLR5) whenever the corresponding channel is engaged. The LEDs may be mounted directly on the PCB or wired off-board through the SW_n connectors.
SW_6 mute optocoupler stage
When SW_6 is activated, the PIC drives the LED side of the TLP181 optocoupler (OC1) via base resistor R13 (1k) and indicator LED D12. The phototransistor side of OC1 sits across the audio output: collector to OUT, emitter to A_GND. While SW_6 is armed, the phototransistor saturates and shorts the output to ground, totally silencing the unit. This is independent of the relay state, so it overrides any active loop.
Signal-line pull-downs
Each effect loop has a 2M2 resistor (R8–R12) from the FROM_BOARD node to A_GND. These very-high-impedance pull-downs drain stray DC charge from coupling capacitors of the effects in the loop, so that switching a loop in does not produce a click or pop from a charged cap discharging through the relay contacts.
Power supply
Power enters at the PWR connector. D11 (1N5817) provides reverse-polarity protection — wire the supply backwards and nothing happens. The post-diode rail VA directly powers the relay coils, the LEDs, the 2M2 pull-downs, and feeds the onboard EFF_n power pins so the boxed-up effects can be powered from the same supply. C1 (100µF) bulk-decouples this rail.
The 7805 regulator (IC1) takes VA and produces the clean 5V digital rail for the PIC. C4 and C5 (100µF) sit on the 7805 input and output, with C2 (100n) as a high-frequency film bypass at the regulator output. A separate analog ground pour (A_GND) is kept distinct from the digital/power ground so that relay coil switching transients do not contaminate the audio rail. There is no factory connection between A_GND and Power_GND on the board — see §06 for the optional star-ground tie.
Bill of Materials
| Ref | Qty | Value | Colour code | Notes |
|---|---|---|---|---|
| Resistors — 1% metal film, ¼ W | ||||
| R1, R2 | 2 | 100 k | Brown · Black · Black | Orange · Brown | PIC reset / MCLR network |
| R3, R4, R5, R6, R7, R13 | 6 | 1 k | Brown · Black · Black | Brown · Brown | Base resistors — relay drivers Q1–Q5 and optocoupler driver OC1 |
| CLR1, CLR2, CLR3, CLR4, CLR5 | 5 | 1 k | Brown · Black · Black | Brown · Brown | LED current limiters. Test value with your specific LED for desired brightness — increase for dimmer, decrease for brighter |
| R8, R9, R10, R11, R12 | 5 | 2.2 M | Red · Red · Black | Yellow · Brown | Signal-line pull-downs to A_GND — drain stray DC for click-free switching |
| Capacitors — Film (non-polarised) | ||||
| C2, C3 | 2 | 100 n | Box film. C2 = 7805 output HF bypass. C3 = PIC supply decoupling | |
| Capacitors — Electrolytic (polarised) | ||||
| C1, C4, C5 | 3 | 100 µF | Bulk supply decoupling — observe polarity (long leg = +) | |
| Semiconductors | ||||
| IC1 | 1 | 7805 | 5 V linear regulator, TO-220. Heatsink not required at this current draw | |
| IC4 | 1 | PIC16LF1826/27P | Pre-flashed microcontroller, DIP-18 — ships programmed for the four operating modes | |
| Q1, Q2, Q3, Q4, Q5 | 5 | 2N5088 | NPN BJT relay drivers, EBC pinout. BC549 works as a substitute but rotate 180° (CBE pinout) | |
| OC1 | 1 | TLP181 | Optocoupler — SW_6 mute. CPC1017NTR is a pin-compatible alternative | |
| D2, D4, D6, D8, D10, D11 | 6 | 1N5817 | Schottky. D2/D4/D6/D8/D10 = relay coil flyback (×5). D11 = reverse polarity protection on PWR input | |
| D1, D3, D5, D7, D9, D12 | 6 | LED 3 mm or 5 mm | Loop indicators (D1/D3/D5/D7/D9) and SW_6 mute indicator (D12). Colour and type of your choice | |
| Relays | ||||
| K1, K2, K3, K4, K5 | 5 | FTR-B3CA-4.5Z | Fujitsu subminiature signal relay, 4.5 V coil, 2-pole. Use fewer than 5 by leaving the unused positions unpopulated and fitting jumpers — see §05 | |
| Connectors & switches | ||||
| JP1 | 1 | 2 × 4 pin header | Mode and loop-count configuration. Set with shorting jumpers — see §05 for the truth table | |
| JX (jumper positions) | 1–4 | Wire jumper, 5 mm pitch | Fitted in the relay coil pads of any unused channel — see §05 | |
| IN, OUT, PWR | 3 | Molex 22-23-2021 (2-pin) | Audio input, audio output, power input — 2.54 mm pitch | |
| SW_1…SW_6, EFF_1…EFF_5 | 11 | Molex 22-23-2041 (4-pin) | Footswitch headers (×6) and effect loop headers (×5) — 2.54 mm pitch | |
| S1…S6 | 5–6 | Momentary SPST | Normally-open momentary footswitch — one per active channel plus optional SW_6 mute | |
Build Guide
Component placement — top-side silkscreen with reference designators
Standard through-hole population order: lowest profile components first, tallest last. Plastic standoffs in the four corners can be used to mount the board.
Resistors
Populate all 18 resistors first — they sit lowest. R1, R2 (100 k); the six 1 k base resistors R3–R7 and R13; the five 1 k LED limiters CLR1–CLR5; and the five 2.2 M signal-line pull-downs R8–R12. No polarity. If you are unsure of a value, measure it with a meter rather than relying on the colour bands.
Diodes
Solder all six 1N5817 Schottky diodes (D2, D4, D6, D8, D10, D11) — observe the cathode stripe against the silkscreen mark. The D1/D3/D5/D7/D9 and D12 LED positions are populated later if you are mounting LEDs directly on the board (see step 7).
IC socket for the PIC
Fit a DIP-18 socket for IC4 (PIC microcontroller). Do not insert the chip yet — leave it in its anti-static packaging until after all soldering is complete. Note the notch orientation against the silkscreen.
Optocoupler
OC1 (TLP181 / CPC1017NTR) is a DIP-4 part — observe the dot/notch on the package against the silkscreen pin-1 mark. A socket is optional but recommended.
Relays
Insert the five FTR-B3 relays K1–K5. They only fit one way around — do not force them. If you are building a fewer-channel version, leave the unused relay positions empty and bridge the bypass pads on those positions with a wire jumper (see §05). Solder one pin per relay first, check the part is sitting flat, then solder the rest.
Transistors
Q1–Q5 = 2N5088, EBC pinout. Match the flat side of the package to the silkscreen flat. If you are substituting BC549, rotate the part 180° because its pinout is CBE (mirror of EBC). Press fully home and clip leads after soldering.
Onboard LEDs (optional)
If mounting indicators directly on the PCB rather than off-board, fit D1, D3, D5, D7, D9 and D12 now. Long leg goes into the square pad. If you are wiring LEDs externally, leave these positions empty — the LED will be wired through the SW_n connector instead.
Film capacitors
C2 and C3 (100 n box film). No polarity, push fully home, solder, clip leads.
Electrolytic capacitors
C1, C4, C5 (100 µF). Polarity matters — long leg = positive, the negative side is also marked with a vertical stripe on the can. Match against the + symbol on the silkscreen.
Headers and connectors
Fit JP1 (2×4 pin header), the three 2-pin Molex (IN, OUT, PWR), and the eleven 4-pin Molex (SW_1–SW_6 plus EFF_1–EFF_5). Insert all connectors before soldering any so they seat co-planar against the board.
7805 regulator
IC1 is the TO-220 7805. Bend the leads at 90° to lie flat against the board if your enclosure is shallow, otherwise mount upright. No heatsink is needed at this load. Observe the pinout silkscreen marking.
Final inspection & insert PIC
Check every solder joint under good light or magnification — look for cold joints, bridges, and missed pads. Verify electrolytic and diode polarities one more time. Power up briefly with no signal connected and confirm the 5V rail at the PIC socket. Power off, then insert IC4 (PIC) into its socket — match the notch to the silkscreen orientation.
Mode Configuration (JP1)
JP1 is a 2 × 4 pin header in the centre of the board. Each of the four pin pairs is one configuration bit — fit a shorting jumper to set that bit to 1, leave it open for 0. Bits are labelled 4 · 3 · 2 · 1 on the silkscreen, with bit 1 closest to the IC4 microcontroller.
| 4 | 3 | 2 | 1 | Mode |
|---|---|---|---|---|
| Operating mode | ||||
| 0 | 0 | X | X | Mode 1 — Standard: each switch toggles its own channel |
| 0 | 1 | X | X | Mode 3 — Fake Radiobutton: one channel at a time, can be toggled off |
| 1 | 0 | X | X | Mode 2 — True Radiobutton: exactly one channel always active |
| 1 | 1 | A | A | Mode 4 — Rotary / cycle (loop count set by bits 2 + 1) |
| Rotary loop count (Mode 4 only — bits 4 & 3 = 1) | ||||
| — | — | 0 | 0 | 2 active loops |
| — | — | 0 | 1 | 3 active loops |
| — | — | 1 | 0 | 4 active loops |
| — | — | 1 | 1 | 5 active loops |
Legend: 1 = jumper fitted · 0 = jumper open · X = don't care · A = use this bit for loop count.
Using fewer than 5 loops
If your build does not use all five channels, leave the unused relays unpopulated and fit a wire JX jumper in the relay coil pads to bridge the signal path through that position. Always start populating from K1 and work upwards — the firmware expects channel 1 to be the lowest-numbered active loop. Bridge K5 down to whichever channel you stop at.
SW_6 — global mute
SW_6 is independent of the operating mode. When pressed (or held, depending on firmware behaviour) it activates the OC1 optocoupler and shorts the output to ground for an absolutely silent kill. Use it as a tuner-mute or between-songs mute. Wiring is identical to SW_1–SW_5.
Up/down counter switches (Mode 4)
In rotary mode, SW_1 cycles up and SW_2 cycles down. The remaining switches (SW_3–SW_5) are unused in this mode and can be left disconnected.
Wiring
Wiring overview — multi-effect mode (left and bottom) plus optional standalone-looper jack wiring (top right)
Power and audio I/O
| Connector | Pins | Function |
|---|---|---|
| PWR | 2-pin | +9 V DC and Power_GND. Wire your DC jack here. Reverse polarity is protected by D11 — wrong-way connection simply does not power up. |
| IN | 2-pin | Audio input from the input jack. Tip = signal, Sleeve = A_GND. |
| OUT | 2-pin | Audio output to the output jack. Tip = signal, Sleeve = A_GND. |
Footswitch connectors (SW_1 … SW_6)
Each 4-pin SW connector carries the switch contact, the channel ground, and an off-board LED option. All six SW connectors share the same pinout — only the channel index differs.
| Pin | Function | Connect to |
|---|---|---|
| SW_n-1 | Switch contact | One terminal of the momentary footswitch |
| SW_n-2 | LED anode (off-board) | + leg of the off-board indicator LED |
| SW_n-3 | LED cathode | − leg of the off-board indicator LED |
| SW_n-4 | SW_GND | Other terminal of the momentary footswitch |
Effect loop connectors (EFF_1 … EFF_5)
Each EFF connector carries 9 V power, ground, and the effect's tip in/out — wire each onboard effect's send and return as well as its supply through this single connector.
| Pin | Function |
|---|---|
| EFF_n-1 | EFF_GND (digital GND on this connector — see note below) |
| EFF_n-2 | + 9 V power feed to the effect |
| EFF_n-3 | EFF_OUT — return from effect output, going back to the loop bus |
| EFF_n-4 | EFF_IN — send from the loop bus to the effect input |
Standalone Looper Build
The Effect-Control can also be built as a standalone external looper — five buffered or unbuffered jack-pair sends/returns, in an enclosure of its own, for chaining external pedals rather than on-board effect modules. The PCB and the configuration are identical; only the EFF_n wiring changes.
Wiring an external loop
Refer to the yellow-highlighted section in the wiring diagram above. For each external loop you want to expose, install a pair of TS jacks (Send and Return) and wire them to the EFF_n connector as follows:
| EFF_n Pin | Wire to |
|---|---|
| EFF_n-1 (EFF_GND) | Sleeve of both the Send jack and the Return jack |
| EFF_n-2 (+9 V) | Not used — leave open if no power is being supplied to external pedals |
| EFF_n-3 (EFF_OUT) | Tip of the Return jack (signal coming back from the external pedal) |
| EFF_n-4 (EFF_IN) | Tip of the Send jack (signal going out to the external pedal) |
Disclaimer & Licence
PCBs purchased from TH Custom Effects are intended for DIY and non-commercial use only. Redistribution of PCBs and artwork from this document is not permitted. You may use these instructions and PCBs to build and sell your own product based on PCBs ordered from TH Custom Effects.
© TH Custom Effects 2014–2026. Build documentation V1.2e.