I am looking for a single-chip implementation of a bandpass filter for audio frequencies, but unsure if they even exist. All the filters I've seen seem to be at least in hundred KHz range. So my question is, do such filters exists?
An ideal filter would be something like:
- A single-chip implementation with minimum extra elements added;
- Reasonably priced (let's say under $10 a piece in bulk);
- Narrow enough (+/-500 Hz is fine for my purposes)
- Offer the binary output - i.e. when the input frequency is 0-350Hz or 450+Hz it outputs logical "0"; otherwise outputs logical "1".
The ultimate goal is to control a block of relays from the soundcard audio output by outputting a specific frequency.
Thank you for reading, and sorry if the question sounds lame - my EE degree is really dusted.
UPDATE: Thanks everyone for answering, but it only took an extra hour of thinking to understand that I can use DTMF. Extra five minutes to find about MT8870. Feeling really dumb now; you guys are awesome!