I'm using an R3, and I'm building an MSGEQ7 project. This requires 5V to power the IC. When I connect the MSGEQ7 circuit to the 5V rail, however, the Arduino goes dead. I can use the 3.3V pin, but I don't think the MSGEQ7 is getting enough voltage and is giving flat readings. I've tried using a 9V 800mA wall plug as well as USB power.
Will I need a second transformer for the MSGEQ7? Is this a problem with my Arduino? Am I just expecting too much draw from the design of the Arduino?
I don't know that IC, but I look for it and I find one reference in sparkfun. This is the datasheet for the MSGEQ7. In pag. 2 you can find the "DC Specifications" and in that table you can see that 3.3V is enough to power the IC, since they say that Vdd must be between 2.7 and 5V. The problem that you have is that the current from your adapter is not enough. If you look to "Supply Current", you can realise that the current consumption can reach the 1000mA. USB can supply 500mA, and your "9V 800mA wall plug" can supply 800mA. The Arduino board have one "power converter" (voltage regulator) that converts the input voltage (in your case 9V) to the voltage level that the board needs to work (5V) that can source a maximum value of 800mA. So, if you can find a wall plug that can source at least 1000mA and 5V (a little more will be better, for example 1200mA), you can connect it to the 5V of the Arduino board and then supply your MSEQ7 with it too, and that will be enough to get it work.
Something must be wired wrong… The MSEGEQ7 itself only requires about 1mA, which is insignificant.
And, all of the 3.3V current is from the 5V supply and it goes through the 5V regulator before going through the 3.3V regulator.
I’m using an R3, and I’m building an MSGEQ7 project. This requires 5V to power the IC. When I connect the MSGEQ7 circuit to the 5V rail, however, the Arduino goes dead.
That sounds like bad wiring (a short-circuit )
Will I need a second transformer for the MSGEQ7?
No, just get the wires in the right place.