Upcycling a Vintage Microphone into an Emergency Radio System -- Episode 663

Clem attempts to create an audio transmission system using two old microphones, exploring the process of converting audio into a digital signal via pulse-width modulation (PWM). He encounters difficulties in getting the analogue system to function properly, detailing the use of low-pass filters, amplifiers, and comparator circuits to modulate audio onto a carrier frequency. Clem shares his understanding of the theory behind the project but admits that the system doesn't quite work as planned.

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Upcycling a Vintage Microphone into an Emergency Radio System -- Episode 663 Transforming Old Microphones into an Emergency Radio System has its Challenges

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We’ve all been there—starting out in electronics, buying a bunch of random parts that seem useful at the time, and then letting them gather dust in a drawer somewhere. For Clem, this collection of forgotten RF modules was no different. After narrowly avoiding the impact of a major flood in his area, he wondered if he could create an emergency communication system with the spare parts from his electronics stash. However, Clem faced a few challenges—not only was he missing some essential components, but he was also diving headfirst into an area he had little experience with: analogue electronics. But hey, that's all part of the fun, right?

A DIY Approach: Building From Scratch

Instead of spending hours researching the perfect setup, Clem did what many of us do: he jumped straight into the project, soldering things together with whatever he had on hand. His base? A retro 1980s microphone and speaker combo, likely used in an old taxi radio system. The original housing wasn’t quite big enough to hold all the necessary components, so Clem 3D-printed an extension ring, using some Proto-pasta conductive PLA he’d received from the element14 community staff for review. This innovative material kept the housing both functional and shielded from interference.

The Antenna Hack

For the antenna, Clem went with the tried-and-true method of using 1.6mm thick tinned copper wire, which he straightened by twisting it in a drill. Classic! To keep things neat, he 3D-printed custom inserts for BNC connectors, ensuring that the antennas were well-isolated from the housing walls. While PLA didn’t quite cut it for this application, MAYER MAKES Engineering Resin was the perfect fit. It had the right tolerances and strength to replace the old nylon inserts, which couldn’t accommodate the new, thicker antenna wires.

First Test Run: Mixed Results

The first test was promising but not perfect. When Clem pressed the button, the unit did send a signal—but it wasn’t quite the sine wave he expected. Instead, it looked more like a digital signal. Curious but not discouraged, he built a second unit, hoping to establish a clear link between the two. And yes, there was a connection! However, instead of the sound he hoped for, the speakers emitted only a faint crackling noise.

Diagnosing the Problem

Armed with a signal generator, Clem injected a known frequency into the transmitter to see how the receiver would react. The result? Success! The devices did indeed communicate with one another, and the signals changed based on the input. The catch? The signals weren’t audio; they were digital pulses—essentially the duty cycle of the input signal being transmitted and received.

That’s when Clem had a light-bulb moment: these RF modules communicate only in digital signals, meaning they transmit data as discrete on/off pulses. To get audio working, Clem would need to encode, transmit, and then decode the audio into a digital format. He sketched out a schematic that combined a known PWM (Pulse Width Modulation) carrier signal with an amplified microphone input. This method would transform the sound into a digital signal that could then be sent over the RF modules.

Is It Worth It?

At this point, Clem had to ask himself: should he continue down this path? The antennas, made to full wavelength, were designed for maximum reception, but the signal range was limited to just a few meters. Plus, 433 MHz RF modules, once groundbreaking, have now been overtaken by cheaper and more efficient options like WiFi modules, which can transmit far more data over greater distances with much better reliability.

So Clem turns to the community for advice: Should he stick with the digital route, using these old RF modules to transmit voice, or go fully analogue and build a proper ham radio-style sender and receiver system? The analogue route could offer more authenticity and simplicity, but digital opens up interesting possibilities. Or perhaps, should he abandon both and pivot to using modern WiFi technology for a more robust solution?

Clem’s project is at a crossroads, and he’s keen to hear your thoughts! Would you pursue the digital RF modules, embrace the challenge of analogue radio, or leap into WiFi for a more reliable emergency communication system? Let him know your ideas and suggestions!

Supporting Links and Files

•  Supporting Files for Episode 663 of element14 presents  

Bill of Materials

element14 presents  |  About Clem  |  Project Videos