this tone generator can be used to control your robot. you will need to use the tone decoder for this. to widen the range, higher or lower - substitute a higher, or lower valued capacitor for c1. for frequencies about 5khz and 15khz, use a piezoelectric element as the speaker. Use a miniature speaker for frequencies under 5khz, and use an ultrasonic transducer for frequencies over 30khz.
all resistors are 5 or 10 percent tolerance, 1/4-watt
all capacitors are 10 percent tolerance,
rated 35 volts or higher