Bring life to your robot with the circuit HT8950 Robot Voice
A must-have gadget for all electronic geeks.

As all electronic geeks, I love robot voices.
This project explain a very powerful voice modulating circuit based on HT8950.
The circuit has Robot function, Vibrato function and 7-step level shifting pitch.
The construction is extremely simple and the unit is very small.
Below you will find MP3 file to hear how a true robot sounds like.
This project comes in a KIT version, see more details below.
All contribution to this page are most welcome!

I have always been fascinated of robots and specially robots which can speak.
A robot should sound as a robot, and true robot sound was first heard during the 80's
in the first computers and pinball machines.

A robot should not sound as a human, they should sound as the evil machine they are.

Why not bring back some true robot sound from the 80's?
The HT8950 is a very amusing little circuit.
With some buttons and some potentiometers, I spent a hole evening finding new interesting sounds.
I had so much fun that I decided to take it to a new level and make a KIT.

This KIT will make you 12 years old again.
Click on rhe picture to enlarge.
  • Microphone input

  • Line input

  • Four buttons to control system

  • Robot voice, Pitching and Vibration

  • Potentiometer to vary pitching and robot sound

  • Potentiometer to vary vibration

  • Two potentiometers to mix input audio with modulated audio

  • Variable gain of microphone

  • LED indication of input signal

  • Output audio amplifier for driving external speaker

  • Power supply +9 VDC to +18 VDC

  • Board size = 2.2" x 1.57" (56 mm x 40 mm)

  • This project comes in a KIT version, see more details below

  • Click on rhe picture to enlarge. Hardware and schematic
    The main part of this project is a HT8950 circuit.
    The circuit runs from 2.4 to 4.0 V and a voltage regulator V1, deliver 3.3V to the circuit pin 7 and 11.
    The audio from the microphone input goes through pot P1 to pin 6. Pot P1 will set the gain of the input signal.
    The intensitivity of the LED indicates the input signal strength.
    Line in is connected to the input as well. Line in should be used with stronger signals from computers, players or instruments.
    If your Line in signal is weak, you can lower the value of resistor R9 (e.g add another 100k on top) o increase gain.
    The input audio from the microphone and the Line in is feed to potentiomer P3.
    With P3 you can decide how much of the un modulated audio (normal sound) you wish feed to the output amplifier.
    At pin 9 you find the audio output of HT8950. The signal is filtered and feed to another potentiometer P2.
    With P2 you can decide how much of the modulated audio you wish feed to the output amplifier.

    By mixing P2 and P3 you can make many combinations with modulated and un modulated audio.

    Potentiometer P4 set the internal frequency and thereby the robot sound frequency.

    Potentiometer P5 set the vibrato frequency of the robot sound.

    Four buttons set the total functions.
  • Robot

  • Vibrato

  • Down pitch

  • Up pitch

  • At the output you have an audio amplifier LM386. Jumper J1 will add 20 times gain if necessary.

    The desoldering wick is a flattened, braided copper sheath	Assembly
    The soldering of this unit is pretty basic. I will explain how to assemble this KIT step by step.
    The PCB is a factory manufacture PCB with high quality, which makes the assembly and soldering simple.
    Please do not be scared for soldering smd parts. Smd is not more difficult than hole mounted parts if you use the correct skills and tools.
    Important tools are good light, soldering tool with thin tip, magnifying glasses, tweezers, thin soldering lead, wick impregnated with rosin and calm mind.

    The de-soldering wick is a flattened, braided copper sheath looking for all the world like shielding on phono cord (except that the shielding is tinned) without the cord.
    The wick is impregnated with rosin. Place the wick over the legs or bridges of the circuit.
    The wick is then heated by the soldering iron, and the molten solder flows up the braid by capillary action. After that, all bridges will be gone and the circuit looks perfect.
    Thin soldering lead and wick impregnated with rosin are included in the KIT.
    Click here to see photo and read more examples how to solder SOIC and smd components.

    Bottom side
    Below you will see the assembly of the bottom side.
  • smd resistors :R1, R2, R3, R4, R9, R10

  • smd capacitors:C3, C6, C7, C11, C12, C13, C15, C17

  • Amplifier: IC2 (make sure you place it in correct direction, pin1 is marked)

  • This is the bottom side

    Top side
    Below you will see the assembly of the top side.
  • smd resistors :R5, R6, R7, R8

  • smd capacitors:C1, C2, C4, C5, C8, C9, C10, C14, C16

  • Potentiometer: P2

  • Regulator: V1

  • 2 Pin header: J1, Line in, Mic, In, Out

  • 3 Pin header: J2, P2, P3

  • 18 pin IC socket: IC1

  • LED

  • Buttons: Robot, Vibrato, Downward, Upward

  • Microphone: Make sure you connect the mic in the correct direction. Most often the minus tab is connected to the house.

  • How to identify the minus and plus tab on a mic.

    This is the top side

    Potentiometer P4 and P5
    Below you will see a picture how to connect potentiometer P4 and P5 to the PCB connector J2
    You need 3 wires (a, b, c) from the pots to J2 on the PCB. J2 is labelled a, b, and c on the PCB.
    In the picture below i use "Linear Dual Taper Rotary Potentiometers", but as you can of course use single taper equally well.
    How to connect pot P4 and P5 to the PCB

    Listen to some example audio files
    Below you can find three mp3 files which demonstrate some audio effects the HT8950 can produce.
    You can hear how I change the frequency and vibrato. I also play with the mixing between normal audio and modulated audio.
    There are so many combination and variation you can make.

    HT8950 sounds
    Robot sound : robot1.mp3 (1.2M)
    Robot sound with vibrato : robot2.mp3 (1.2M)
    Pitch sound : robot3.mp3 (1.2M)

    Order a KIT
    which will include all parts

    The Robot Voice KIT includes all parts, manual, soldering lead, and wick.

    Order here
    Below you can find different options for ordering, click the links for detailed information.

    Trouble Shooting section
    If you get a problem with your unit, you might find this section helpful.

    Check this!
    Make sure the IC1 and IC2 is placed in correct direction.
    Make sure you have +3.3V to pin 7 of IC 1.
    Make sure you have +1.2V at pin 10 of IC 1
    Make sure the soldering of he parts are well done.
    Make sure you have connected Pot 4 and 5 correct to J2.
    Sill having problem...take a break and get some air.
    You can always e-mail me

    Final word
    I hope you have enjoyed reading about this Robot Voice project.
    Hopefully you have found new inspiration for your own projects.
    Thanks for your time…

    Front side
    Here you have it. Few parts and perfect function.

    Back side
    Here you have it. Few parts and perfect function.

    I'll be back...

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    Copyright © Last modified on 5 Feb 2011.