MSGEQ7 Graphic Equalizer with OLED Display

Elektor magazine gives a continual stream of great ideas for electronic projects.  About 9 months ago I saw a project which utilises MSI MSGEQ7 chips in a 7 channel spectrum analyser / graphic equaliser.  This little chip is ideal for creating a bar display showing an audio frequency response.
I tried it out with a Neopixel display and a small OLED screen.

Design

Hardware: I initially intended to use a NodeMCU ESP8266, but the software library appears not to support ESP8266, so I moved to an Arduino nano.  Neopixel and 0.96" OLED displays were used.
Input: Initially PC line out used for testing, L and R channel signals were combined. Final solution needed to work on hi-fi using RCA or Digital audio Jongo output.
Software: Nico Hood's MSGEQ7 is principal Arduino library providing the necessary functionality.
Output: Initially console output used to understand MSGEQ7 values, then dots, then bars were used for each channel.

Circuit

Nico Hood provides a lovely informal circuit diagram for the MSGEQ7.

The chip provides 7 values each time the input is sampled and these are obtained on the output pin using the strobe pin.  Frequency ranges are defined  using a 200k resistor and 30pF on pin 8.

Three pins were connected to the arduino nano: Strobe (D2), Reset (D3), Output (A0).  A further pin (D9) on the arduino was used for a neopixel display.

Testing

Nico Hood's library demo program worked well and I was quickly able to see what values are being output by showing them on the serial monitor.  There is a "noise" level of about 16 (in 8 bit value) which I subtracted.  I then scaled the remaining values and  translated them to dots on the Neopixel and got a fast responsive display.  I then replaced dots by bars and put caps on the bars.  To avoid excessive flicker on the display I only sent changes each cycle rather than re-displaying the entire screen.

The OLED B&W (£5) display provides some fine detail but it isn't as interesting as the Neopixel colours.  A 0.96" colour display is about £15 - a bit high for a little circuit.  OLED screen updates are responsive and look convincing.  

RCA analog and digital output can also be used.  To use the digital output I need to convert the signal to analog, I purchased a PROZOR 192KHz DAC convertor for about £5 to do this. Pure Jongos provide both formats so I can attach a "VU meter" at the same time as connecting Jongo to Hifi.