FFT or discrete bandpass filters

[Caleb_P]

I am adding a music visualizer to my current project and need some advice. The circuit has a MCU, LED display with driving hardware and a microphone with an opamp. I want to get the magnitude of a few frequencies and display corresponding animations on the LEDs. I can do an FFT on the MCU but I'm trying to maximize sleep time for power efficiency reasons. Running an FFT and doing lots of ADC measurements will drastically reduce battery life. My other option is to select 4 frequencies and build 4 second order pass band filters. I can then rectify these 4 AC frequencies using a diode and have a Resistor and Capacitor in parallel. This would give me an approximate magnitude reading for each frequency.

Do you think it is worth the effort and extra cost to add the analogue front end or just take the hit on battery life? I plan for my project to be produced in small quantities (100-1000) but I am still concerned about cost. Any advice would be appreciated.

[nctnico]

You can implement 4  IIR filters (elliptic 2nd or 4th order). These take little processing power if your MCU has a hardware multiplier.

[Caleb_P]

Thanks nctnico. I will look into the efficiency of that compared to the other two options.