I'm having a little problem coming up with a reasonable way to complete a circuit. I would like to be able to drive 6 continuous ultrasonic outputs. Each output would range from roughly 22KHz to 40KHz. The outputs need to be individually frequency controllable. For example, output zero would be at 34 KHz and going up at 200KHz per second, output one would be at 29KHz and going down at 100KHz per second, etc. The climbing/falling speed and direction of the outputs would need to be software controllable.
I've looked at using the PWM6 on a processor such at the ATTINY861. But, it appears to be operating the outputs at the same frequency, just modifying the pulse width. I've tried using software to generate the output frequencies on a single ATTINY861. But, I have not been able to get the output frequencies with the resolution I would like to see with only a 20MHz clock and timer1 with an output compare interrupt.
One option is to use 6 ATTINY13's, one for each output. This would work, but I would like to know if anyone has a better / more elegant solution. (Using one IC to generate the frequencies would be nice)