A relay board for performing blind A/B testing of two audio sources.
This version of the board is designed around parts available from Tayda electronics.
See the thread at diyaudio.com.
This board design is open source hardware, released under the terms of the MIT license. It requires an ancient version of Kicad (sorry, not sorry 😝). Debian users will need to add a jessie source to install the libpng12 dependency.
Changes from v4:
- Include missing base resistor R28.
- D4-6: three 1N5817 Schottky diodes.
- Any diode will work, but the lower voltage drop of Schottky diodes extracts more useful life from the 9V battery.
- Tayda
- D7-10: four LED's.
- Any color. 3mm or 5mm.
- Tayda
- D11-22: twelve 1N4148 diodes.
- Flyback diodes. Any diode will work here.
- Tayda
- R1-4: four 220R 1/4 watt resistors.
- LED current limiting. Tune the resistance value to get the LED brightness you prefer.
- Tayda
- R5-7,20-22: six 100k 1/4 watt resistors.
- Voltage dividers for Arduino inputs. 5% carbon film or 1% metal film.
- Tayda
- R8-19: twelve 100k 1/4 watt resistors.
- MOSFET gate pull-up and pull-down resistors. 5% carbon film or 1% metal film.
- Tayda
- R23-27: six 10k 1/4 watt resistors.
- PNP base current-limiting resistors. 5% carbon film or 1% metal film.
- Tayda
- SW1-3: three miniature micro switches.
- Tayda MX1382-F91
- Q1,3,5,7,9,11: six 2N3906 PNP BJT transistors.
- Tayda
- Any TO-92 PNP transistor which can handle 100mA (with an EBC pinout) will work fine.
- Q2,4,6,8,10,12: six 2N7000 N-channel MOSFETs.
- Tayda
- Any TO-92 N-channel MOSFET which can handle 100mA (with an SGD pinout) will work fine.
- K1-6: six 3V latching relays
- Tayda FTR-B3GB003Z
- CON1-3: three 3.5mm headphone jacks
- IC1: one Arduino Nano board.
- Any $5 Arduino Nano board on ebay will work fine.
Choose one:
Changes from v3:
- Use 2N3906 PNP BJT's which are cheaper than BS250 P-channel MOSFETs (and are available from tayda)
- Use wider traces for the signal path.
Changes from v2:
- Add test points to input X and Y for volume matching convenience.
- Use pins RX0, TX1 instead of A6, A7 (which cannot be used a digital outputs).
This release fixes a couple of bugs from v1:
- Replaced the 100k input resistors with proper voltage dividers.
- Fixed the silkscreen outline of the relays.