Today’s IR-based remote controls have little resemblance to their predecessors; it took the convergence of unrelated advances to get us here.
Part 1 examined dead-end precursors to our present-day remote-control technology; this part examines the IR-based system now in near-universal use.
Back to the future: the convergence of UHF bands, electronic tuning, and LEDs re-opens an old idea
Managing the mechanically based VHF TV tuner was always challenging, as electronic RF switching as we know it today did not exist. The remote-control function required a motor-rachet mechanism to physically turn the tuner rotor, just as a hand-on knob would. Not only was this awkward and slow, but it limited the channel control to sequential up-and-down cycling.
Electronic-based tuning started to appear in the 1960s for two reasons. First, the solid-state variable-capacitance diode (varactor or varicap) was developed and commercialized, significantly contributing to enabling electronic tuning. Second, the broadcast TV range of channels expanded from VHF to add UHF frequencies (designated as channels 14 to 83, 470 to 890 MHz) as there was a need for more channels (stations). In 1965, the FCC made UHF tuners mandatory in all US TV sets. Note that with the need for more spectrum for other uses and the adoption of digital TV, the FCC reallocated the upper block of UHF channels in the 1990s.
Developing a tuner for these UHF frequencies was a significant challenge due to the tight channel spacing concerning the center frequency, the impact of RF parasitics on design, layout, and production at these frequencies, and other factors. A UHF tuner, separate from the VHF tuner but located in the same TV chassis, was a tribute to design complexity and sophistication (Figure 1).
These UHF filter circuits were capacitively tuned using three variable “air blade” capacitors, in contrast to the “drum tuner” for VHF. The non-constant blade radius provided a constant-frequency tuning behavior, but the performance was very finicky, and using a mechanism to tune the channels would be an additional challenge. Eventually, the VHF and UHF tuners were combined into a single assembly, but each half still had its circuitry due to the vast differences in frequencies and associated components.
That’s where varactor-based tuning came into use. The channels could be electronically tuned by varying the DC bias on the diode via a control circuit (Figure 2). This eliminated the mechanism with all its benefits.
Tuning control improvement did not stop with the inclusion of the varactor. The next step was tuning based on the phase-locked loop (PLL) and direct digital synthesis (DDS — also called synthesized tuning)) using a single crystal to establish a near-perfect master clock from which all channels could be derived. Not only was this accurate and precise, but it was extremely flexible, fast at switching randomly from channel to top channel, and offered an electronic channel-indictor readout.
At the same time, the unrelated development of red and infrared (IR) light-emitting diodes (LEDs) provided a low-cost, easily controlled light source that could be on/off modulated at a high rate and with crisp edges, unlike the incandescent bulb. This LED is controlled by a small keypad arranged as a matrix and modest electronics in a handheld, battery-powered remote control (Figure 3).
An IR-based remote-control receiver, Figure 4, consists of a PIN diode or phototransistor to capture the photons, an automatic gain control (AGC) to dynamically adjust for variations in intensity (the user may move around while using the handheld unit, or there may be variations in ambient lighting or optical noise), filtering, and a demodulator, with a suitable modest control function.
The demodulated signal is then passed to a microcontroller, which decodes the on/off bit pattern in accordance with the designated format to indicate what action the system should take.
A plethora of formats
Once the IR-based tuner became a standard component in the 1980s, product manufacturers had to choose a modulation, data format, and protocol. Not surprisingly, each major vendor decided on a proprietary scheme to “lock in” users to their product line so a single remote control could be used with their TV display, set-top box, VCR, DVR, and other devices. That tactic lasted only for a few years as universal user-programmable remote controls soon became available, which could be set to support almost any coding arrangement.
The remote-control data is sent in serial format, with the data stream encoded using several different modulation techniques. These techniques determine how the zeros and ones are formatted for transmission over the infrared light beam. Three basic modulation techniques are used, along with several variations of them.
- Pulse density modulation (PDM), also called space encoding or pulse distance modulation
- Pulse width modulation (PWM), also called pulse encoding
- Bi-phase modulation, also called Manchester encoding
The modulation technique is only part of the story, as the format used to encode the desired action is another factor. Nearly all IR remote controls use a 940-nm optical wavelength and 38-kHz modulation rate. However, many protocols are in use, some of which are vendor-specific and others used by multiple vendors (Figure 5).
These protocols define critical parameters, including:
- The modulation technique used
- The timing and format of the start bit
- The number of addresses and data bits
- The format of any error checking used
- The format of the end of the message (EOM) or stop bit(s)
- Whether the data is the least significant bit (LSB) or the most significant bit (MSB) first
For example, the packet of the popular NEC protocol begins with a 9-msec leading pulse burst followed by a 4.5-msec space (Figure 6).
There’s much more to say about formats and protocols, but that is outside the scope of this article. See External References for links to additional sources.
Conclusion
The IR-based remote control is a marvel of technological advancement and is also noteworthy because its final implementation is so removed from its origins. The path from initial design to our present-day embodiment was not a smooth evolution; instead, it was a series of disruptive transformations made possible by unrelated technical developments.
It transitioned through wired, simple light, ultrasound, and infrared implementations in conjunction with advances in all-electronic tuning via varactors, PLLs, synthesized (DDS) tuning, and the development of the IR LED. While remote controls were originally driven by the needs of TVs and related units, they have expanded into use with almost any large or small appliance or gadget due to their low cost, reliability, and functionality.
Related EE World content
RCA & Color TV: A dominant company and standard, both now gone – Part 1
RCA & Color TV: A dominant company and standard, both now gone – Part 2
Synthesized tuning, Part 1: Basic frequency-synthesizer principles
Synthesized tuning, Part 2: Advanced synthesizers and performance
Radio receiver architectures, Part 1—TRF and Superhet
Radio receiver architectures, Part 2—Zero-IF and SDR
FAQ: What is a Phase Locked Loop (PLL)?
External references
Maximus R&D, “Philips TV Tuner History pt2: 1958-1963 Introduction of UHF and the last valve tuners”
The Verge, “The buttons on Zenith’s original ‘clicker’ remote were a mechanical marvel”
Zenith, “Six Decades of Channel Surfing”
CNET, “Remembering Eugene Polley and his Flash-Matic remote”
The Register, “Wireless remote control inventor zaps out at 96”
Lemelson-MIT, “Robert Adler: TV Wireless Remote”
Historic Tech, “Zenith Lazy Bones- 1st Successful TV Remote Control”
DroneBot Workshop, “IR Remotes Revisited – 2023”
IEEE Spectrum, “The Day the U.S. TV Industry Died”
ME TV, “A history of the TV remote control as told through its advertising”
Jasco Products Company, “Universal Remote Code List”
Vishay Semiconductors, “Data Formats for IR Remote Control”
Circuit Basics, “How to Set Up an IR Remote and Receiver on an Arduino”
Autodesk Instructables, “Simple IR Remote Controls”