Retro Engineering: TV Remotes

Or: How would you control your TV in the 1950s?

In this article, we're going to delve into the design of "clickers," or old TV remote controls from the 1950s. This marks the first installment in our retro-engineering series, where we examine past engineering designs to gain insight into the methodologies engineers employed. With the benefit of hindsight, we can discern which designs succeeded and which did not. By reverse-engineering the processes behind successful designs, we can glean valuable lessons in sound engineering practice.

Let's begin by exploring how these clickers functioned.

You might be aware—or perhaps not—that these clickers operated using sound. Inside each clicker were several metal bars. When tapped, these bars resonated at specific frequencies, each corresponding to a particular television function: changing channels, adjusting volume, powering the TV on or off, and so forth.

Pressing a button on the clicker activated a spring-loaded toggle mechanism, causing a small hammer to strike the appropriate bar. This produced a clear ringing sound at an ultrasonic frequency, inaudible to the human ear. From the user's perspective, the experience was akin to using modern remote controls.

Understanding the mechanics of these clickers allows us to critically assess the development process behind them.

Firstly, it's noteworthy that the designers accurately identified user needs. From an outcome-driven innovation perspective, this was spot on. Users preferred the convenience of controlling the television without the need to physically approach it – it made the job to be done much easier.
This necessity raised the question: how to transmit the user's command to the television?

This framing led to two critical considerations: the nature of the signal and the medium through which it would travel.

Potential options at the time included:

• Infrared signals, akin to those used in many modern remotes.
• Radio waves, similar to those employed in remote-controlled toys.
• Wired connections, as seen in some early remote controls.

However, each of these options had drawbacks. Infrared and radio wave technologies were prohibitively expensive due to the cost of components (recall Moore’s Law where electronics have been regularly halving in size and cost while doubling in power for decades now) and the limitations of battery technology at the time. Wired connections, while feasible, were cumbersome and detracted from user convenience.

Consequently, engineers had to explore alternative solutions. Sound, particularly ultrasonic frequencies, emerged as a viable option. By applying fundamental principles, they realized that the natural frequencies of metal bars could be harnessed to generate distinct signals.

This realization reframed the design challenge: creating a handheld ultrasonic transmitter.

Because TVs were already established, along with the internal technoilogy, it was possible to create a circuit to process the signal from the microphone using vacuum tubes. They were not transistor type electronic devices that are the subject of Moore's law. Therefore, it likely would have seemed quite obvious that the microphone should be attached to a circuit to activate the respective switch depending upon the frequency of the signal reaching the microphone and being converted into the electrical signal. I don't want to be dismissive of this though, it still would have been a design challenge and an engineering challenge, it's just that it probably would have flowed a lot more after the previous frame, designing an ultrasonic generator that can be held in one’s hand, was formed.

For a more detailed history of TV remote controls, you can refer to Zenith's heritage page: Zenith Remote Background.

Now here’s a question for you: would you have conceived the same solution under similar constraints? Contemplating this can provide deeper insight into your own engineering skills and how to further develop them.
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Additionally, if you have alternative ideas for creating a remote control using 1950s technology, feel free to share them in the comments. Personally, I pondered the use of inductors and capacitors to filter the microphone's signal into the respective circuits as an alternative to vacuum tubes. That’s because I recall making a filter for a speaker box I made some time back, and I have a fixation on such filters. So also think about what made you come up with the your idea.