Music Spectrum and dB Visualizer

• Yesterday all of the parts came in, electrical components from Digi-key and the PCB from JLCPCB
• Soldering tools such as flux paste and tweezers came in from amazon
• Currently watching videos on different ways to Solder

• Verified BOM, replaced components that are currently out of stock
• Order remaining components on Digi-Key
• Bought tools needed for SMT soldering on Amazon
• Ordered PCB on JLCPCB

• To save time, only made 'absolutely necessary corrections'
  • Oriented R82 and D71 correctly in schematic
  • Added 0.1uF decoupling capacitors for op amps 
  • Moved decoupling capacitors closer to IC it is supporting 
  • Moved ports closer to the edge
  • Added reverse voltage protection at the power port
  • Added stitching vias

• Started making BOM
  • Sourcing everything from Digi-key
  • Started sourcing components on Digi-key, down 15 out of 91
  • Made a mistake in the footprint from some of the capacitors, some are non-stocked on Digi-Key and or Mouser, all of the issues were resolved

Posted schematic and PCB on Reddit for a design review - https://www.reddit.com/r/PrintedCircuitBoard/comments/xo5yta/design_review_audio_visualizer/

• Add stitching vias to the ground pour
• Use the thickest traces I can get away with
• Don't daisy chain the power connections, use star formation
• Be mindful of physical construction of the plugs
• Move capacitors closer to the IC it is supporting
• At 0.1uF Low ESR caps to power pins of op-amps
• R82 & D71 should point downward, not to the right. (in the schematic)
• J2 (DC power jack) should have reverse voltage protection
• Add high impedance input buffer to filter section to avoid unnecessary loading, such as a JFET op amp, could also just use extra op amp in each filter section as the buffer
  • If I don't use the extra op amps, consider tying them together

• Finished Tracing +/-5V power
• Traced Brightness and volume range control
• Found "Phoenix Contact 1725656" Terminal Block to connect Male audio jack to
• Traced audio input and mode header
• All nets, subcircuits etc. have been routed, now will commence with design review, then doublecheck BOM, then order PCB!!!

• Applied copper ground fill to top and bottom layer
• Ground pads of IC's where filters were traced were not connected from the copper pour:
  • created new topology to remove problem
  • Successfully retraced Sub-bass and bass filters

• Got 3D models for all components
• Formatted and aligned all the sub-circuits in the PCB editor
• Found a PCB design fundamentals resource http://alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf and posted (at the time) current PCB with LED driver and 2 filters traced on Reddit for a design review
  • PCB making is subtractive process, better to keep traces as thick as possible and keep a ground fill unless there is a reason to not have one
    • Will have a ground pour on both the top and bottom layers
    • Set grid to mils
    • Power traces will be 50 mils, everything else will be 10 mils
    • Don't be afraid to use vias
    • rotate components to make tracing easier
• Added 7th LM324 Quad-op amp IC to filter arrays, now each spectrum filter will have their own op amp IC
  • Will allow traces of different stages of the same spectrum filter to go to the same IC
  • Will be easier to route and read in the PCB - more aesthetically pleasing
  • Minimizes trace length
• Added 10uF polarized filter capacitor for the LEDs
• Traced 9V power, sub-bass and bass filter
• ***Will use JLCPCB to manufacture the PCB, even though the minimum order is 5 and along with at least 2 have to be assembled if that is what I choose to do, it is still the cheapest option by far

• I originally decided to use KiCad over CircuitMaker for its ability to simulate circuits.  However:
  • Circuits with IC's take a long time to simulate, even if it is quite simple
  • When their is feedback and/or if the IC contains multiple circuit elements (e.g. LM324 IC has 4 op amps) the correctness and ability to even simulate at all is in question
• Already made the all of the active filters in KiCad, remaking them in CircuitMaker would take a really long time since the topology of each filter is slightly different and their values are very different
• The only other large sub-circuit is the LED driver, the driver circuit for each frequency spectrum is exactly the same so I can make them once and copy and paste for the rest

• Will be using LM324DR2G IC for filter op amps, 1.2mA supply current
  • 6 ICs x 1.2mA/IC = 7.2 mA
  • Worst case scenario, audio signal voltage is >=3.5V, max current output by all filters is 6mA
  • 7.2mA + 6mA = 13.2mA
• Max Current output of Rhi controller will output is 1.4 mA + 17uA supply current from the Op-amp 
• Max Current Sourced From Dual Rail Power Supply: 13.2mA + 1.417mA  = 14.617 mA
• Will establish -5V with LT1054IPE4 - it is a converter and regulator in one, just needs and external resistor network
  • ***One of the smoothing capacitors is supposed to be 2uF, but the cheapest one is $1.32, therefore I will be using 2 1uF caps to replace it
  • ****In order to simulate in LTSpice consistently make sure the box for "Skip initial operating point solution" is checked

• It was found than when a pull-down resistor is connect to pin 5 (signal input pin) of the LM3915 IC, the port would output ~0.14uA = 140nA, therefore limiting the value of the resistor to 1kohm so that a voltage of no higher than 0.14mV DC would develop
• Therefore, for the high-pass RC filter to be appended to spectrum filters, R = 1 kohm
  • Sub-Bass and Bass: C = 100uF  
  • Low-Mid and Mid: C = 10uF 
  • Upper-Mid, Presence and Brilliance: C = 1uF
• The capacitors I have at home that have a capacitance of greater than or equal to 10uF are polarized, but ceramic capacitors exists for up to 100uF, maybe even higher, but they get more expensive
  • 1u: $0.11 to $0.138 
  • 10u: $0.138 to $0.152 
  • 100u: $0.607 to $0.713
• Calculated max current each filter and internal stage will output when amplitude of input voltage signal is 5V (output at final stage will be saturated to 3.5V):

• Say signal was completely in the Brilliance spectrum, max outputted current would be 5.345mA.  The 3.6mA output of stage 3 is completely due to the 1k ohm resistor of the high-pass RC filter.  Assuming each op amp IC which contains 4 op-amps requires 1.5 mA, which there are 6 of -> 6*1.5 = 9 mA

  • 9mA + 5.345mA= 14.345 mA.  Negative Voltage multiplier can output a current of 17mA and still stay below 8V, so we are in the clear