New version of the electronic constructor. Transmitting sound through light

This article is a continuation of the previous article about the electronic constructor. In the comments to the previous article, several valuable comments and suggestions were made, which I tried to put into practice. I also tried to make a small circuit for transmitting an audio signal via a light signal.

Changes in the designer

In general, the design of the constructor – the division of parts into platforms and plates – remained the same. Screw clamps also remained, as the easiest to make at home and reliable to use.

Below are the main changes made in the new version of the designer:

• The platforms are attached to the substrate using magnets. Magnetic marker boards of the required size are used as substrates. Now the parts can be positioned anywhere on the substrate. In addition, the weight and height of the entire structure have been slightly reduced, and there is no longer any need for manual production of the substrate, in particular, the tedious drilling of a large number of holes in it.
  
• The plates with parts are also attached to the platforms using magnets. At the same time, no modernization of the plates themselves was required, which is good news, since a fairly large number of them have already accumulated. Initially, there were concerns that the strength of the magnets would not be enough to ensure reliable contact between the plate and the platform, but practice has shown that the contact is quite reliable and there are no problems.
• Instead of nuts, threaded rivets are used to attach connecting wires. These rivets have internal threads only on the upper half of the rivet, so they are easier to position on the screw and require fewer turns to tighten. It is also convenient to attach an oscilloscope probe and alligator clips to these rivets.
  

It seemed to me that fork tips would not be very convenient to use, since during assembly all the connecting wires are usually thrown on first and then the rivets are screwed in. It is clear that fork tips will fly off the screws with this approach.

Transmitting sound using light

To demonstrate, I tried to build a device for transmitting audio signals using light. The transmitting side converts the audio signal into light by changing the brightness of a laser diode, and the receiving side receives the light signal and converts it back into sound.

As a source of light signal I have a laser module DSP6505-0818, similar to a regular laser pointer, but with power wires brought out. As a receiver of light signal is used a phototransistor, which increases its conductivity with increasing illumination.

Since the light intensity must change both upward and downward when transmitting a signal, the laser module must shine in the absence of a signal, but not at full power. Then it will be possible to both decrease and increase its brightness. As a result, the following transmitter circuit is obtained.

The laser module L1 is connected to the power source via the current-limiting resistor R1. This resistor provides moderate brightness of the laser module. In my case, a 240 Ohm resistor was suitable. The laser module is also connected to the input audio signal via the separating capacitor C1. As a result, fluctuations in the input signal cause voltage fluctuations on the laser module and, accordingly, fluctuations in its brightness.

The capacitance of the capacitor C1 must be large enough to allow low frequency oscillations to pass through freely. The larger the capacitance of the capacitor, the better, I have the largest capacitance capacitor I have available.

The diagram of the receiving side is shown below.

Phototransistor T1 is connected to the power source via resistor R2. Fluctuations in the light signal cause changes in the phototransistor conductivity and, accordingly, fluctuations in the current and voltage on the resistor. Resistor R2 is selected so that the voltage on it in the absence of an input signal is approximately in the middle between zero and the supply voltage and, accordingly, can fluctuate both downwards and upwards. If the voltage on the resistor is too close to zero or to the supply voltage, then you can change the brightness of the laser module using resistor R1 on the transmitter.

Resistor R2 also controls the amplitude of the signal transmitted to the Low Frequency Amplifier (LFA), thus acting as a volume control. The amplified LF signal is fed to the speaker. As an amplifier I use ULF BM2036

You can watch a video of the device in operation here: