Bioprobe (MA063E)

An interesting article dealing with electric fish (The Electric Fish Named Black Ghost (BM027E)) shows that these animals produce electrical signals in the audible range from 700 to 2,100 Hz for orientation purposes in water. We can hear these signals if we connect to the aquarium they are in with a common audio amplifier and also pick up these signals for other purposes.

Our small amplifier lets us hear these electrical signals, making them audible sounds. Of course, there are other electrical phenomena which occur in living beings that, being in the audible range, can be converted into sound through the use of a small amplifier. We then describe in this article two small amplifiers which can be used in the lab to hear these signals on a small speaker.

Certainly, its use will arouse much curiosity and enrich any biology class. Both circuits are battery powered and therefore fully safe to use.

The Circuit

Both circuits consist of sensitive audio amplifiers which can work with the few millivolts of signals we encounter in the most common biological phenomena.

The first is quite simple, using three transistors capable of delivering a small amount of audio power to a speaker. We find a volume or gain control between the first and second stage and the circuit is powered by only two small batteries.

In Figure 1, we have a small box suggestion in which it can be built, observing that in this box we have a suggestion for using a headset.

Figure 1 - Box Suggestion for the Assembly

The complete diagram of this amplifier version is shown in Figure 2.

Figure 2 - Diagram of the first amplifier | Haga click en la imagen para ampliar |

To hear signals of an electric fish (see article), we have in Figure 3 how to prepare the electrodes which should be placed in the aquarium.

Figure 3 - The electrodes | Haga click en la imagen para ampliar |

For the second version, we use a TBA820S integrated circuit.

This component is no longer as easy to find nowadays, but we can adapt the circuit to operate with today's most popular integrated devices like the LM386 and TDA7052. The circuit for this version is shown in Figure 4.

Figure 4 - Circuit with an integrated amplifier | Haga click en la imagen para ampliar |

The printed circuit board for the transistor version is shown in Figure 5.

Figure 5 - Printed circuit board for the transistor version | Haga click en la imagen para ampliar |

If the reader wants to make an experimental assembly on a breadboard, in Figure 6 we give the arrangement of the components.

Figure 6 - Assembly on the breadboard | Haga click en la imagen para ampliar |

When assembling, take a good look at the positions and types of the transistors, as Q3 is different from the others.

For the integrated circuit version, we have the printed circuit board in Figure 7.

Figure 7 - Printed circuit board for the integrated version | Haga click en la imagen para ampliar |

Note in this version the position of the integrated circuit and transistors, as well as the polarities of the electrolytic capacitors.

To test is simple: holding the input wire, our body picks up the noise of the power grid which turns into a snoring that is reproduced in the speaker.