Analog Circuit to Switch LED Using Two Different Sound Frequencies (No Digital ICs)

Hello, I am working on a project and I need to design a circuit that turns on an LED using an xxxHz sound frequency and turns off the LED using another xxxHz sound frequency. The project can use any passive elements, but nothing digital!!!! Can use electret microphones, resistors, capacitors, relays, op-amps etc... I do not want a specific circuit diagram but just general input on what some may think the best way to achieve this would be, i was thinking about rectifying the microphone output to DC voltage, and using op-amps to amplify the signal, which would drive a latching relay circuit that controlled the LED, but i have been having trouble properly rectifying and amplifying the audio signal. 

John...if you rectify your audio (you can do this with an op-amp circuit called a precision rectifier, google it), you will lose all frequency information and will not be able to use different frequencies.What you could do is have two tuned circuits and rectify their outputs and use whichever one is activated for the function you need.There is a lovely chip called a 567 tone decoder that would do what you want, but I don't know if you'd be allowed to use this - it would count as an analog IC but maybe they'd see it as cheating.....If you're going to use tuned circuits, get the right inductance/capacitance parallel combination  for each frequency you are using, feed them from your audio source (amplified first if necessary) via a fairly high value resistor (10 K or more) and then use a precision rectifier to rectify the signal of each tuned circuit.  You then  need to turn the led on whenever that voltage goes over a certain value - you could use a zener diode for that.You could also use op-amps and make some narrow band-pass filters instead of the tuned circuits.  There are many ways of doing this - google band pass filters for more.  There is a circuit called a twin-T filter and you can find calculators for this and other filters on the net.Good luck with it, come back if you need more help.

My interpretation of your requirements: Burst of first trequency turns LED on. After burst ends, LED stays on. Burst of second frequency turns LED off. After burst ends, LED stays off. Is this correct? To remember the on/off state of the LED, you suggest using a latching relay. You could also use a flipflop. To make a flipflop and pretend it's analog, look up "bistable multivibrator". You can build an RTL (resistor-transistor logic) flipflop from two NPN transistors and a few resistors. You could also use a gate-turn-off thyristor (GTO) or a unijunction transistor (UJT) in a bistable mode. The programmable unijunction transistor (PUT) is closely related to the GTO, both being-four-layer devices.You can build a four-layer device from an NPN transistor and a PNP transistor: Tie each transistor's collector to the other transistor's base. The PNP emitter is the anode. The NPN emitter is the cathode. The NPN-base, PNP-collector junction is the gate. The PNP-base, NPN-collector junction is the complementary gate.Good audio-frequency inductors are hard-to-find nowadays. The primary winding of a commonly-available power transformer or audio transformer will work well as an audio inductor.You might want to look up the frequency-discriminator and ratio-detector circuits used in analog FM radios.Pulse-width-discriminator circuits also exist. Use a comparator to convert your input sinewave to a squarewave to drive the pulse-width discriminator. One way to build a pulse-width generator: Build a monostable multivibrator whose output pulse width is halfway between (half the period of the high-frequency squarewave) and (half the period of the low-frequency sinewave). Trigger the monostable on the rising edge of the squarewave, and sample the squarewave on the trailing edge of the monostable output: For the high frequency the sample will be low, and for the low frequency the sample will be high.