ATtiny212 Firmware for Distortion Pedal

cherepanyadima

cherepanyadima

Please analyze this schematic carefully. The relay coil now works and K2 clicks, but the distortion effect does not work when the relay switches to the NO / effect position.
The project is a guitar distortion pedal with relay bypass.
Important context:
  • U2 is ATtiny212.
  • PA1 drives Q2 relay driver.
  • K2 is Omron G6S-2F 5VDC relay.
  • D2 flyback diode was found reversed during testing and was temporarily removed. Please verify its correct orientation.
  • Relay coil works now, but when the relay switches, the distortion path does not produce sound.
  • I need you to check whether the schematic routing is correct, especially the relay audio contacts, VREF, analog power, and mute/photorelay circuit.
Please analyze these points:
  1. Relay K2 audio routing: Check the exact relay pinout and footprint for Omron G6S-2F 5VDC. Verify if the relay contacts are connected correctly.
For bypass / relay OFF:
  • JACK_IN_TIP should connect to BYPASS_LINK.
  • JACK_OUT_TIP should connect to BYPASS_LINK.
  • The signal should bypass the distortion circuit.
For effect ON / relay energized:
  • JACK_IN_TIP should connect to EFFECT_IN.
  • EFFECT_OUT should connect to JACK_OUT_TIP.
  • BYPASS_LINK should be disconnected from the active audio path.
Please explicitly tell me:
  • In relay OFF state, which nets are connected?
  • In relay ON state, which nets are connected?
  • Is COM/NC/NO mapping correct for this relay footprint?
  • Is the footprint possibly mirrored or using bottom-view pin numbering incorrectly?
  1. D2 flyback diode: Verify D2 orientation. Correct expected orientation:
  • D2 cathode / stripe side should connect to +5V / relay coil positive.
  • D2 anode should connect to RELAY_COIL_NEG / Q2 collector / relay coil negative. If D2 is reversed, explain what happens and confirm how it should be installed.
  1. Q2 relay driver: Confirm that Q2 is wired correctly:
  • PA1 → R4 → Q2 base.
  • R5 pulls base to GND.
  • Q2 emitter goes to DGND.
  • Q2 collector goes to RELAY_COIL_NEG. Expected ON state:
  • PA1 = 5V.
  • Q2 base = about 0.6–0.8V.
  • Q2 collector / RELAY_COIL_NEG = about 0–0.6V.
  • Relay coil has about 4.5–5V across it.
  1. U4 photorelay / mute circuit: Please analyze U4 carefully. It appears connected around EFFECT_OUT and GND/DGND. Check if U4 can mute or short EFFECT_OUT to ground. Tell me:
  • Is U4 intended as anti-pop mute?
  • Should U4 be ON only briefly during relay switching?
  • Should U4 be OFF during normal effect ON operation?
  • If PA6 keeps U4 ON, could it completely mute the distortion output?
  • What should PA6 logic be during bypass, switching, and effect ON?
  1. VREF and analog power: Check the analog section. Verify:
  • +9V_CLEAN reaches the op-amps.
  • VREF is generated correctly by R9/R10 and capacitors.
  • VREF should be approximately half of +9V_CLEAN, around 4–4.5V.
  • All op-amp reference inputs that need VREF are connected.
  • No op-amp input is floating.
  • The analog ground and digital ground are connected correctly.
  1. Distortion signal path: Trace the full effect signal path and confirm it is complete:
  • EFFECT_IN
  • input buffer
  • BUFFER_OUT
  • gain / clipping stage
  • DRIVE_OUT
  • tone section
  • volume/output section
  • EFFECT_OUT
  • relay output to JACK_OUT_TIP
Please identify any possible missing connection, wrong net label, floating node, or incorrect capacitor/potentiometer wiring that would make the distortion path silent.
  1. Potentiometers: Check the gain, tone, and volume potentiometer connections. Make sure:
  • wipers are connected to the correct nets.
  • end terminals are not swapped in a way that shorts signal to ground.
  • volume output actually reaches EFFECT_OUT.
  1. Clipping diodes: Check D3/D4 clipping diodes. Verify they are connected to the correct gain stage nodes and not accidentally shorting the signal.
  2. Provide a measurement checklist: Give me a step-by-step list of what to measure with a multimeter:
  • +9V_CLEAN to GND
  • VREF to GND
  • EFFECT_OUT to GND resistance with power off
  • JACK_IN_TIP to EFFECT_IN continuity in relay ON
  • JACK_OUT_TIP to EFFECT_OUT continuity in relay ON
  • JACK_IN_TIP to BYPASS_LINK continuity in relay OFF
  • JACK_OUT_TIP to BYPASS_LINK continuity in relay OFF
  • PA6 state and whether U4 is muting
  1. Provide a likely fault list: Based on the schematic, list the most likely reasons why the relay switches but the distortion does not work.
Do not write firmware yet. First analyze the schematic and give me:
  1. Relay routing truth table.
  2. VREF/power verification.
  3. U4 mute analysis.
  4. Possible schematic/footprint mistakes.
  5. Measurement checklist.

flux

7:25

Thought for 17 sec

Read K2 datasheet for pin configuration contact arrangement te.

Read U4 datasheet for pin configuration input output photorela.

Read U2 datasheet for pinout pin configuration ATtiny212 SOIC .

Read BOM.

Read schematic.

Read schematic.

Read schematic.

Read schematic.

Read schematic.

Found 1 results for Omron G6S-2F-DC5 datasheet pinout COM NC NO pins 3 4 5 8 9 10 bottom view.

Completed 3 design checks — found 141 issues.

I found two high-probability causes: K2’s COM/NC pin mapping in the schematic appears inconsistent with the Omron G6S-2F pinout, and U4 can mute EFFECT_OUT if PA6 is held HIGH. D2’s schematic orientation is correct: cathode/stripe to +5V, anode to RELAY_COIL_NEG.
Full relay truth table, VREF/power review, U4 mute logic, fault list, and measurement checklist are in Relay Distortion Path Debug Analysis.
Fix K2 mapping
Corrected relay table
Trace effect path
Check U4 mute
Run ERC/DRC
Sign up to send
EFFECT_IN
R7
Resistance
1MΩ
R8
Resistance
1MΩ
EFFECT_OUT
JACK_IN_TIP
R6
Resistance
1MΩ
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Modern Distortion effect pedal V1

Modern Distortion effect pedal V1 thumbnail
Modernlow-noise distortion effect pedal for electric guitar. This pedal provides adjustable gain, tone, and volume control with relay true bypass and soft-touch footswitch operation. The design includes LED status indication, anti-pop mute switching, reverse polarity protection, and separated analog and digital power sections for improved stability and reduced noise. The project uses an ATtiny412 tinyAVR 1-series microcontroller for control logic, a TPS70950 voltage regulator for the digital supply, OPA1656 audio op-amps for the analog signal path, a G6K-2F-Y-DC5 relay for bypass switching, a TLP3431 photorelay for anti-pop mute control, and BAS16 diodes for symmetrical clipping.

Properties

Properties describe core aspects of the project.

Pricing & Availability

Distributor

Qty 1

Arrow

$7.95–$10.74

Digi-Key

$8.31–$11.00

HQonline

$4.92–$4.95

LCSC

$14.45–$14.49

Mouser

$26.32

TME

$12.72

Verical

$1.21–$22.37

Controls