voice1.jpg (4904 bytes)

The recording module

voice3.jpg (4456 bytes)

Preparing the relay

voice4.jpg (3321 bytes)

Attaching the alligator  clips

voice5.jpg (7410 bytes)

Attachment points for  relay assembly

voice6.jpg (5298 bytes)

The completed voice  module

voice7.jpg (6989 bytes)

Module attached to Scout brick

This is a quick one evening project to add voice capability to your robot. In our example we are making a module for the Lego Mindstorms system kits, but any robot with the ability to switch output voltage to a relay can use this module as well.

One advantage of our system is that it is quite inexpensive -- all of the parts will cost less that twenty dollars. The other is simplicity. The system is very simple, just record and go. There is no fancy programming or advanced technique required to build or operate the system.

The base module for our robotic voice is a twenty-second recording module that we obtained at a local Radio Shack store. The module is shown in its original form in the top picture at the left. This module is completely self-contained with the exception of a nine-volt battery. As you can see from the picture, there are two buttons on the module. The button connected by wire is the recording button while the onboard button is the playback button.

The other parts necessary for our project include a five-volt reed relay, a 220 ohm resistor, and two feet of light gage wire. The part numbers for the project parts are included near the end of this page.

The first step for the construction portion of the project is to prepare the reed relay. Referring to the picture at the left, bend the two prongs for the relay coil at a 90 degree angle. A 220 ohm resistor is soldered to either coil prong. A short 1 inch piece of wire is soldered to one of the contact prongs. Finally, two 12 inch pieces of wire are attached to the other coil prong and to the resistor as shown.

Note that the coil resistance is 250 ohms. Since the RCX and Scout brick motor outputs supply nine volts, we chose the 220 ohm value to lower the voltage across the coil prongs to about 5 volts. The actual voltage in our example is :

9V * 250/(250+220) = 4.79V

The resistor value can be changed based on the supply voltage and relay voltage by changing the values in this formula.

The next step is to attach the alligator clips to the ends of the 12 inch wires. We chose these clips to make our voice module versatile, but another option would have been to cut a standard Lego wire in half and attach it to the module in place of the 12 inch wires and clips.

Now for the trickiest part of the procedure. The relay is attached to the recording module at the points shown at the left. One end is attached to the black battery wire mounting point, while the one inch wire is attached to the last resistor where shown. It does not matter which wire is soldered to each point since the relay merely closes the same circuit that the play button does. It is important to use a low wattage soldering iron for this part of the procedure to avoid damage to the circuit board.

Once the relay assembly has been soldered to the recording module, the construction portion of the project is complete. The next step is to attach the nine-volt battery to the module's battery clip, then press the record button and record a short message.

If you chose to use the Lego wire attached to the recording module, simply attach the wire to the "A" motor output, choose program one on the RCX brick (or choose "forward" on the Scout brick) and press the run button. Using the alligator clips, attach the wires to the two top prongs of the "A" motor output, making sure that the clips contact the metal portion of each prong. If assembly is proper, you should now here the module speak. If not, its time to check connections.

This is a great project to add voice to your robot due to the low cost and time involved to complete the project. We had fun with it and in the future will have our next Lego robot talking up a storm.

Project Parts List:

20 second recording module RS # 276-1323
5VDC reed relay RS # 275-232
Mini alligator clips RS # 270-380A
220 ohm resistor
25 inches light gage wire
9 VDC battery