I am at the edge of RAM and speed with the ATMega. So I got myself finally a Teensy 3.1. With a 74HCT245 bus tranceiver I got the ouput to 5V. So far it works fine and drives the WS2812B. Wicked fast.
Now I would love to attach my MSGEQ7 shield. Schematic is here: http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Dev/Arduino/Shields/SpectrumShield-v14.pdf
The shield is made to run on 5V, the MSGEQ7 specs say 3,3V is fine too. On the shield that (3,3V) pin is not connected. So I wonder if it is ok to just give the 3,3V from the Teensy to the 5V pin on the shield, connect the 2 data pins and the 2 analog ins. Vcc seems to be connected directly to the msgeq.
Is there any reason in the schematic not to do so?
Per the schematic, it looks like on the right side of the IC, theres a resistor between VCC and the chip @200k ohms. you may need to check out the MSG’s datasheet to see what resistor you really need at 3.3v
I have the 5V pin on my MSGEQ7 board hooked to the 5V pin on the Teensy and it works great.
Hi Jason, which 5V pin??? Or which Teensy? I thought they are all running on 3,3V. And if I power the MSGEQ7 with 5V that would cause a higher output and by that a higher voltage to the analog ins. I learned that controllers are pretty sensitive to input voltages higher than Vcc. So I would need a volatage divider in that case?!
The teesny takes 5v from the USB and regulates it to 3.3. You can tap the via right next to the USB on the teensy to access the 5v VUSB
Ah, the USB power, thanks John! On the breadboard I have already the 5V from the led bus driver. So how to limit the output of the MSGEQ7 to a digestible level for the processor?
You need one of these for the MSG chip’s analog out: https://www.adafruit.com/products/395
Or this would work better:https://www.adafruit.com/products/735
The bi-directional is overkill, but handy to have around
From the Teensy forums: “the (digital and anlog) pins can’t measure over 3.3V, even though they’re able to tolerate being driven up to 5V” and “if the voltage is above 3.3v, analog reads will just return 1,023” http://forum.pjrc.com/threads/26317-teensy-3-1-analog-input
@Jason_Coon https://www.pjrc.com/teensy/teensy31.html
Only the DIGITAL pins are 5v tolerant!
LOL, yes John, that is exactly the chip I am using to drive the leds. A 74HCT245. And he has still 7 free inputs…
But I mean the analog output from the MSGEQ - how to get that analog level shifted? Voltage divider?
Pins 14-24 (A0-A9) are digital and analog, and are 5V tolerant, right? Only A10-A14 aren’t? https://www.pjrc.com/teensy/pinout.html
That would be great! Where is it written?
Here’s a link to the forum asking the same q: http://forum.pjrc.com/threads/25979-5v-AREF-on-Teensy-3-1
That thread is asking about connecting AREF, which is not one of the 5v tolerant pins, to 5v. The last post in the forum thread I linked above has Paul saying the pins that are both analog and digital (A0-A9) can tolerate 5v, and they’ll just return 1023 for anything over 3.3v.
…and getting the answer that it “will very likely damage the chip”. So it is about designing a voltage divider with 2 resistors?
I did not see your post above, Jason. Sorry. So if I give up to 5V to the analog pins I just loose precision when measuring them. Good, that the ADC has 12 bit. 
Now I have all the informations I need for my setup tomorrow. Great!
Thanks for you support guys!
Maybe step back and try a different approach?
With teensy power you could probably go FFT and do away with the MSGEQ7 entirely
@Stefan_Petrick https://www.adafruit.com/products/1780
I have one of these, and Kevin is right about the FFT. You can get 256 bins of eq data. What would you do with all those values? hmmm
Well, I like the msgeq because he is really fast and precise. I would prefer to keep the processor with more layers and merging effects busy.
FFT: Are you talking about 256 different bands? Ideas are invading my mind immediately… How much processor load does the FFT cause? Or how much time does it need to get one set of data with lets say 7 bands? Just to compare it with the msgeq.