Retro Multiband Radio With Oscilloscope

This project involves building a retro multiband radio receiver, mimicking the appearance of a laboratory instrument, in this case, an oscilloscope.

The following basic components are required for this project:

- Multiband radio receiver module.

- Audio amplifier.

- An old video camera for parts.

A detailed list of all the necessary parts for this project is provided later.

The project will be built using modules that can be easily purchased online (multiband radio module and audio amplifier) ​​and other components obtained from disassembling a video camera (CRT) and a laptop (speakers).

The enclosure will be made of plastic using a 3D printer.

It is assumed that you have knowledge of electronics and high voltages, as well as the associated health risks. Therefore, anyone who decides to reproduce this project assumes all associated dangers at their own risk. The most critical modifications to the circuits will be shown in images; likewise, the parts of the case assembly, supports, etc. have been omitted (since this document was compiled once the project was assembled and no photos were taken during certain processes).

Radio Module:

Multiband FM/MW/SW Headphone Radio Module

Operating Voltage Range: 3V

Headphone Jack: 3.5mm diameter jack

Product Dimensions: 60mm * 32mm * 43mm

Frequency Range:

FM 87 MHz - 108 MHz

MW 513 kHz - 1629 kHz

SW1 5.75 MHz - 12.15 MHz

SW2 12.95 MHz - 18.05 MHz

Audio Amplifier:

TDA2030 Audio Amplifier Board Module.

Features:

1. Integrated TDA2030A audio power amplifier chip.

2. 18W mono amplifier.

3. Integrated 10K adjustable resistor for volume control.

4. Power indicator.

5. Operating voltage: 6-12V.

Mini CRT:

Obtained from the finder viewer of an old video camera (from the 1990s in this case).

Operating voltage: ~6V (in this case).

1 – Type C lithium battery charger board BMS 2S 4A 18650.

1 - Antenna, it is obtained from an old radio or other device that you have at home for parts, or if not, you buy one.

1 - Toggle switch (replaces the OFF/FM/AM switch).

1 - 100K linear potentiometer to replace the audio amplifier trimmer (the value will depend on the one used in the original amplifier module circuit).

1 - 10K multi-turn potentiometer to replace the original one in the radio module; improving tuning, especially on shortwave.

1 - 4-position, 3-pole rotary switch (replaces the two original switches: power and band change).

2 - 6mm 3V metal LED warning indicator lights (replace the power and tuning LEDs).

2 - Laptop speaker with its enclosure (in my case, these came from a disassembled laptop).

2 - 18650 3.7V 3000mAh lithium battery.

1 - 470uF 10V electrolytic capacitor.

2 – Volume and band switching knobs, 25 mm diameter.

1 – Tuning knob, 50 mm diameter (in this case, 3D printed).

1 – Optical glass magnifying lens, 20 mm diameter (obtained from a video camera lens).

1 – Cellophane in your preferred color (placed behind the lens to create a realistic oscilloscope appearance); I chose green.

1 – Various screws for assembling the enclosure and modules.

2 - Aluminum sheet of 4 mm and 1.5 mm

Initially, the concept and appearance of the device are considered, as well as the efficient and correct placement of all modules to eliminate hazards and interference caused by the CRT circuit.

First, a simple sketch of the front of the device is created. German lettering is chosen to give it a more understated and authentic look.

A mounting bracket for the CRT tube is planned, which will then be created and 3D printed. This will require disassembling the video camera's finder viewer and extracting the circuit board containing the CRT tube. Next, the bezels surrounding the CRT must be removed, leaving it bare. Depending on the type of video camera, the screen may be circular or square.

Example:

Basic structure with two sections: separators A are made of 4 mm thick aluminum sheet; element B is made of plastic, as is the top part to conceal the aluminum. Aluminum is used to create a Faraday cage to isolate the CRT circuit and prevent interference in the medium and shortwave bands. Later, 1.5 mm thick sheets are added to the sides and back of the first section (where the CRT is mounted).

1 – 18650 battery holder.

2 – Radio receiver module holder.

3 – Speaker mount.

4 – Antenna mount.

5 – USB-C connector for battery charger.

- The battery holder is removed.

- The tuning potentiometer is replaced with a 10K multi-turn potentiometer.

- The bi-color LED is replaced with two 6mm metal LEDs.

- The power and band selection switches are replaced.

Legend of the connections of the switches (C is the common for each pole), the two switches are replaced by the 4 position and 3 pole rotary switch, adapting it; and On/Off is bridged later the toggle switch for starting up in the main supply is added.

- Two wires will be soldered in the places indicated for antenna input (ANT) and audio output (Audio out); at the CRT mark (audio output for the CRT) the positive of a 470 uF electrolytic capacitor will be connected and at the negative a wire will be soldered which will then be connected to one end of the vertical deflection coil.

- Identify the ground, positive input voltage, and correct input voltage connections.

- Identify the vertical deflection coil wires. If they are not easily identifiable, first determine which pairs of wires belong to each coil, and then simply disconnect one pair to identify which one belongs to the vertical deflection coil. Connect the module to the correct voltage, and if a horizontal line appears on the screen, the vertical deflection coil is disconnected (which is what is needed). If, on the other hand, a vertical line appears, the horizontal deflection coil is disconnected.

- Once the vertical deflection coil has been identified and disconnected, connect the horizontal deflection coil to where the vertical deflection coil was connected, thus driving the CRT tube.

- We will use the vertical deflection coil to inject the audio signal and thus display the waveform as an oscilloscope. Therefore, we will remove that pair of wires from the coil to connect them later in the appropriate place.

- The trimmer potentiometer will be replaced with the 100K linear potentiometer (it was replaced here with a 100K potentiometer to protect the speakers).

- The audio input will be connected to the cable we prepared earlier and labeled 'audio out'.

- A simple common power supply circuit will be built using general purpose diodes (SMD M7 were used here) and an LM1117 3.3v voltage converter to power the radio module, adding the toggle switch as the main start-up switch.

- We will verify if the modified radio receiver module is functioning correctly.

- We will verify that the amplifier is functioning correctly by connecting its output to the speakers and testing it by injecting an audio signal into the audio input.

- We will verify that the CRT circuit is functioning correctly by displaying a horizontal line.

- We will test the desired operation of the CRT by injecting an audio signal into the prepared vertical deflection coil (audio output shield to one end of the coil and live wire to the other). If everything is working correctly, it should display some kind of wave pattern; depending on the volume of the audio signal, it will appear larger or smaller. It may not display across the entire width of the screen, it may be out of focus, the beam may not be centered, etc.; these details will be corrected later.

- We will verify that the common power supply circuit is functioning as intended.

- Connect all the grounds of each module (CRT, Radio, Amplifier, Battery Charger) to the ground of the common power supply circuit.

- Connect the positive terminal of the CRT to the output of diode D2 (SMD M7), which will provide an output voltage of approximately 6.5-7.4V, sufficient for the circuit used in this project.

- Connect the positive terminal of the amplifier module to the output of diode D3 (SMD M7), which will provide an output voltage of approximately 6.5-7.4V, sufficient within the module's operating range.

- Connect the positive terminal of the radio receiver module to the output of diode D4 (SMD M7), which will provide an output voltage of 3.3V, also sufficient within the module's operating range.

- Connect the charging output of the battery charger module to the positive terminal V1 of the power supply circuit.

- Connect the audio output of the radio receiver (Audio out) to the input of the audio amplifier. - Connect the negative terminal of the 470 µF electrolytic capacitor, previously soldered to the CRT mark, to one end of the vertical deflection coil; connect the other end of the coil to ground.

- Leave the wire soldered to the ANT (antenna) mark loose and insulated for testing to prevent accidental contact with any part of the circuitry.

- Insert the batteries and turn on the device. If everything is working correctly, all modules should function, produce sound through the speakers, and display a waveform pattern of the sound received by the receiver.

- Adjust the main volume using the radio module's trimmer to avoid distortion.

- Check how the beam is displayed on the CRT; it will most likely need adjusting. These adjustments are made using small trimmers located on the CRT circuit. Experiment until you achieve a sharp, focused image that fits the screen width and is horizontally centered. Some CRT models only have a couple of trimmers; in this case, you will need to adjust the position of the coil (which is held in place by a threaded nut) forward or backward, as well as the small toothed rings that move the beam's position. When performing this operation, be extremely careful not to touch any solder joints or uninsulated wires directly with your fingers. It goes without saying that handling these types of circuits is dangerous due to their high voltage.

- The MW and SW bands will be tested; you may hear buzzing noises due to the proximity of the CRT circuit. Therefore, it must be electromagnetically isolated from the rest of the project using a grounded Faraday cage. This point is important because if it is not grounded, it has no effect on the circuit.

- Prepare the 4 mm and 1.5 mm thick aluminum sheets.

- Print the necessary parts.

In my case the position of the stickers needs to be improved.

The final result is reasonable considering the materials used and the modifications made – replacing the tuning potentiometer with a multi-turn one – except for the antenna, which isn't long enough for shortwave. Even so, it was possible to tune in to some foreign stations.

And that's how 56 hours of work are spent on a whim.

P.S. No AI was used to generate this tutorial. Please be kind to this project, as it's the first one I've done for instructables.com.