MSGEQ7 7 Band Graphic Equalizer Chip

I had bought a couple of MSGEQ7 chips in 2014 from eBay with plans to do something with them. So recently I found myself a bit of idle time and mounted one on the breadboard to try it out. I used the circuit straight out of the MSI datasheet (Figure 1):

Figure 1. MSGEQ7 Circuit

I had a little trouble getting this to work correctly, so I scoped pin 8, knowing this is not going to be accurate but should indicate if the RC oscillator was running at all or not (Figure 2). The trace indicated about 102 kHz, which is probably higher with the 10x scope probe removed. 

Figure 2. Trace of pin 8 (Oscillator)

The problem was that I was getting an output (pin 3), like that of Figure 3. This was with no signal applied.

Figure 3. Incorrect outputs (pin 3)

After trying several things including gain and frequency adjustments of the function generator, I decided to try the other chip (I always buy two for this reason!) This chip swap yielded the type of results I was looking for (Figure 4):

Figure 4. MSGEQ7 finally works (near 60 Hz)

The tallest signal represents the first frequency bucket which represents about 63 Hz (from the documentation). This will vary somewhat depending upon the internal RC oscillator.  I used a AVR generated oscillator to strobe this thing and used the scope's sync to drive the reset. You can see two complete traces in the middle with partials at the ends. Unfortunately the Rigol internal hardware frequency counter didn't like the low signal levels. The software frequency measurement likewise didn't grok the low function generator signal levels either.

Figure 5 shows the result of the function generator at 160 Hz. I found that the signal generator (B&K Precision Model 3050) needed to be on the 0 dB output range at about 10%. The chip was fussy about the input level going from no output to all high when the signal went out of range.

Figure 5. 160 Hz

 The next bucket is 400 Hz, shown in figure 6.

Figure 6. 400 Hz

 Figure 7 shows the 1 kHz bucket activated.

Figure 7. 1 kHz

 Setting the function generator to 2.5 kHz for the next bucket (Figure 8).

Figure 8. 2.5 kHz

 Figure 9 shows 6.25 kHz.

Figure 9. 6.25 kHz

 Finally figure 10 shows the last of the seven buckets activated with 16 kHz.

Figure 10. 16 kHz

The idea behind the chip seemed cool. I had planned to drive it from an ATmega328P, hooked up to a Raspberry Pi. But having tested it out I quickly realized that this circuit is much too finicky for a "simple project". What it needs is a circuit ahead of the MSGEQ7 with AGC to keep the signal within acceptable limits. Otherwise the MSGEQ7 will simply disappoint.

The MSGEQ7 is a CMOS chip. I was aware of this and took my usual care handling it. But the first chip may have been static damaged on the breadboard. If you choose to breadboard it, I recommend that you make all the connections without the chip and plug it into the breadboard last. This is the first damaged CMOS chip I've had in quite a long time (it might even have been damaged as part of the shipping process).

You can read more about the MSGEQ7 chip from this PDF file:

  https://www.sparkfun.com/datasheets/Components/General/MSGEQ7.pdf

Thanks for reading.