Free Modular

RNG Assembly Instructions

See general assembly instructions

Components

See general components notes for more info about acquiring parts.

Interactive BOM: front, back

Board Reference Part Value Source Comment
Front R1, R20 Resistor 100kΩ    
Front R2, R3 Resistor 1kΩ   Determines output impedance. Any value is fine.
Front R4-R7 Resistor 10kΩ   Determines LED brightness. You may want to use a different value if you have different LEDs. A lower value means less resistance and brighter LEDs
Front RV1-RV3 Potentiometer B50kΩ Thonk Linear. Any value is fine.
Front D1-D11 LED 3mm   Any standard 3mm LED will work here.
Front SW1 Rotary Encoder EC11 series Amazon  
Front SW2, SW3 Switch TAIWAY 200CWMSP1T3B4M2 Love My Switches, Thonk SPDT ON-ON
Front J1-J6 3.5mm Jack THONKICONN (a.k.a PJ398SM or PJ301M-12) Thonk  
Both J8-J10 Pin headers 2x3, 1x8, 1x8 Amazon Solder the two boards directly together using the male headers or (recommended) make them detachable using a male/female pair.
Back J7 - -   Not used. Expansion points for future features
Back J12 IDC connector 2x8   Eurorack power header. Can use two rows of male pin headers or (recommended) a shrouded connector.
Back R8-R11, R14-R15 Resistor 100kΩ    
Back R12, R13, R16 Resistor 50kΩ    
Back R17 Resistor 1kΩ   Determines output impedance. Any value is fine.
Back R18 Resistor 15kΩ   Controls the LED brightness for the 7-LED display. Unlike the bottom LEDs, which are in series with R4-R7 (at 5v), this resistor is just used as a current reference (at 5v) by the TLC5940. To match the current across all the LEDs (and therefore the brightness), R18 is calculated by R18 = 5 / ((5 - V_LED) / R4), where V_LED is the voltage drop across one of the LEDs (at the current they will receive). This can be measured or will probably be in the LED datasheet. Then, round to the nearest available resistor value; it doesn’t have to be exact.
Back R19 Resistor 15kΩ   Controls the available current at the -5v ref regulator. You could probably go a little higher to be more power efficient, but if the -5v voltage sags you can decrease the value.
Back C1-C5 Capacitor 100nF   Optional. Power supply noise filtering capacitors
Back C6-C8 Capacitor 10uF   Optional. Power supply noise filtering capacitors
Back C6-C8 Capacitor 10uF   Optional. Power supply noise filtering capacitors
Back A1 Arduino Nano v3.0    
Back U1 LED driver TLC5940NT DigiKey  
Back U2 DAC MCP4922-E/P DigiKey  
Back U3 Op-amp MCP6004 DigiKey  
Back U4 Op-amp TL072 DigiKey  
Back U5 Voltage regulator LM4040BIZ-5 DigiKey 5v, TO92-3 package