By merging a digital potentiometer with an oscillator chip, we can make a very small programmable oscillator (1 uMAX and 1 SOT23 package). Not only does this circuit take up very little board space but it can be controlled with only three signals from a microprocessor.
The MAX5160 is a 200K digital pot with 32 taps. To move up to the next tap, set UP/DOWN high and pulse INCREMENT low. To move down, set UP/DOWN low before pulsing INCREMENT.
The LTC1799 is a programmable oscillator from Linear Technology. The frequency of oscillation is proportional to the value of the set resistor between V+ and the SET pin. Internal to the chip is a divider which is controlled by the DIV pin. The following table illustrates the relationship between the divide ratio and the input on DIV: