A robot voice generator circuit is a device which modifies a normal human voice into a typical robot like voice, that we normally come across in movies, or video games.
The working concept of the circuit is actually simple. The actual human voice signal is subjected to an external frequency modulation signal, such that the voice audio is attributed with an intriguing vibrating quality which resembles a robot voice closely.
You can get a similar robotic voice output if you try speaking in front of a table fan, spinning at a high speed.
How the Circuit Works
The figure below shows a circuit that may be used to generate computer-like or robot like voice effects for community theater plays, or other similar applications. This sort of circuit is identical to a tremolo circuit in many respects, however the modulating signal is almost always a squarewave.
A straightforward astable multivibrator constructed around Tr1 and Tr2 provides the modulation signal in this example.
Due to this, a mark space ratio of somewhat lower than 1:1 appears to produce the best outcomes, and also C4 and C5 may not be of identical values, as they might be in a “coursebook” astable.
Slowing down the rise time of the modulation signal produces a somewhat better output audio, and this is accomplished by inserting a simple R/C low pass filter (R5 and C3) between the astable output and the Tr3 gate.
Tr3 is implemented in a standard VCA that also includes R6 and R7.
C1 and C2 serve as DC blocking capacitors, while C6 serves as a supply decoupling capacitor.
The circuit has the effect of modifying the input voice signals to two degrees of attenuation, the highest of which is approximately 26 dB greater than the lower, which results in the production of the robot like manipulated sound.
The modulation oscillator “breaks up” the signal by switching it between these two levels with a frequency of many Hertz, giving the desired robotic voice effect.
Despite the fact that this circuit employs the most commonly adopted technique of electronically creating a computer-generated voice effect, it performs admirably in practical use.
The input signal level can be as high as a few volts peak to peak without causing any overloading issues. S1 controls the on/off switch. The circuit draws around 1 milliampere of current.
You will need an audio amplifier unit hooked up with the output of the circuit for hearing the robot voice loudly over a loudspeaker.