You are asking for a Voltage Controlled Oscillator. It can be made out of a 555 like the Drawdio is but the wiring is a little different. Here is one of many hits I found when I searched for "555 VCO circuit".http://ecelab.com/circuit-vco-555.htm
You may find the high/low pitch reveresed from what you want, depending on the ciruit. Or it may be exactly as you want.