Reliability



Custom Solutions, Inc. recognizes that reliability is of great concern to anyone purchasing or installing a home control system. Therefore, HomeVision, HomeVision-PC, and HomeVision-Pro were designed from the ground up to provide many years of reliable operation. During the design process, we sometimes made decisions that delayed its release or increased its manufacturing cost, but which were necessary to ensure reliability. Even now, our manufacturing and testing process takes longer than many of our competitor's because of the stringent procedures we have in place. We accept these added burdens because they give our customers a highly reliable product, upon which our reputation rests.

The lead HomeVision designer was previously employed by a major, multi-billion dollar defense electronics company for over 20 years. While employed there, he was responsible for the reliability of numerous electronics systems used on military aircraft, communications satellites, the Space Shuttle, and similar programs. He brought many of the same reliability concepts to HomeVision's design and manufacture. This article describes many of these techniques, focusing primarily on the hardware issues. Discussing software bugs (and how we catch and squash them) would require a whole other article.

 

Minimizing Electrical and Thermal Stresses

We must minimize stresses on components so they operate continuously for many years without degradation:

bulletResistors and capacitors operate well below their maximum power and voltage ratings.
bulletInfrared transmitter LED (light emitting diode) operates well below maximum current, voltage, power, and temperature ratings.
bulletHigh-intensity green LEDs minimize current draw, power dissipation, and temperature.
bulletLow-power CMOS integrated circuits lower power dissipation and temperature.
bulletPower regulator rated at 1 Amp or higher. Actual current draw is typically 100mA, and maximum is 400mA, providing significant margin against part rating.
bulletRegulator mounted directly to circuit board with heatsink to minimize temperature.
bulletPower regulator contains over-current and thermal shutdown circuit to protect against power-to-ground shorts and overheating.
bulletDiodes protect against voltage spikes on TW-523 interface to minimize chance of overstress.

 

Robust Electrical Design

The electrical design must ensure the circuitry works 100% of the time, regardless of component performance drift, temperature, aging, use environment, etc.:

bulletMicroprocessor operates well below maximum allowable clock speed to maximize circuit timing margins.
bulletMemories are faster speed than necessary to guarantee error-free operation.
bulletWorst-case circuit analysis performed to ensure circuits function properly over a wide temperature range even after device aging.
bulletHigh-capacity battery, in conjunction with extra low power RAM, ensures memory retention after 12 years without power for HomeVision and HomeVision-PC.  The HomeVision-Pro battery will last at least 4 years without power, and is easily replaceable by the user.
bulletClock adjustment factor implemented in software to reduce drift of real time clock.
bulletHigh-performance electrolytic capacitors used (lower-quality ones degrade rapidly over time).
bulletTwo infrared receivers achieve exceptional performance. Performance has been verified using a standard TV remote from over 80 feet away in a "noisy" environment with large amounts of fluorescent and incandescent light.
bulletUndervoltage detector circuitry shuts unit down as soon as power begins to drop out. This prevents erratic operation that can result when parts operate at low voltages.
bulletPrecision components in the video oscillator circuitry improve video timing accuracy.
bulletHigh-performance video switch passes video signal through controller without degrading picture quality.
bulletExtra-strong video output level drives long cables without an external amplifier (this high level sometimes requires the addition of an attenuator to maximize picture quality; however, we felt that this was a worthwhile tradeoff to save many of our customers the cost of an external amplifier).

 

Parts Quality

Part quality is critical in preventing failures:

bulletParts are chosen from high-quality suppliers we're familiar with, not just anyone. Parts from new suppliers are thoroughly evaluated and tested before being approved for use.
bulletHigh-quality terminal blocks provide secure clamping of interface wires.
bullet"Dual-leaf" sockets make superior electrical connections with the integrated circuits than less expensive "single-leaf" sockets.

 

Software Design

The software must verify proper hardware operation and use robust control methods:

bulletSelf-test automatically runs at start-up and tests critical circuitry:
bulletEEPROM
bulletRAM
bulletProcessor
bulletPeripheral control circuits
bulletSerial port chips for HomeVision-Pro
bulletContinuous error checking and recovery methodology ensures reliable operation.
bulletHardware watchdog timer restarts entire unit if software ever locks up or performs unexpected operations.
bullet"Polite" X-10 transmissions won't interfere if other transmissions are in process.
bulletX-10 collision detection and retry to improve transmission reliability.
bulletPrecise X-10 timing pulses transmitted to TW-523 ensures transmissions always meet the X-10 specifications (even while HomeVision is receiving an infrared signal and performing other operations simultaneously). Three-phase transmissions are far more accurate than in some of our competitors' systems.
bullet32-command X-10 input buffer stores received X-10 signals so HomeVision won't miss anything.
bulletStandard infrared receive signal format uses 16-bit error checking to eliminate false triggers. Ambient light won't ever accidentally trigger an action.
bulletInfrared signal "learning" process measures the signal's carrier frequency to accurately reproduce the signal. Some of our competitors require you to guess the frequency yourself and use trial-and-error to verify it.
bulletInfrared transmitter can vary the signal's duty cycle, allowing you to increase or decrease the signal's power output. This can be helpful when using mini-emitters that sometimes overpower the receiver they're attached to.

 

Electromagnetic Interference (EMI) Control

EMI can cause erratic circuit performance and "glitches" if not properly controlled:

bulletMultiple bulk decoupling capacitors support current requirements of high-power devices (to control L di/dt noise and "ground bounce").
bulletNumerous high-performance ceramic filter capacitors minimize high-frequency switching noise.
bulletPower distribution system minimizes ground loop areas (to control radiated emissions) and trace impedances (to control L di/dt noise and "ground bounce").
bulletHigh-performance HC (high speed CMOS) integrated circuits maximize signal noise margins.
bulletCircuit board ground shields around and under sensitive circuitry (particularly the video and infrared receive circuits).
bulletMetal enclosure provides shielding from radiated emission from TV's, stereos, etc.

 

Manufacturing and Testing

We must minimize defects in the manufacturing process and catch any that do occur with thorough testing:

bulletAutomated board assembly process minimizes chances for human error and increases product consistency.
bulletElectro-Static Discharge (ESD) controls prevent ESD damage to sensitive ICs.
bulletAll units "run in" for at least 40 hours to stress the hardware and eliminate any possible defects. All functions are continuously tested, including X-10, video, infrared, and I/O ports. Units are only shipped if they run PERFECTLY. A single glitch causes the unit to be rejected (after which the cause must be found and corrected and the unit run for 100 hours without problems).
bulletAll units subjected to two complete functional tests (one prior to "run in", one afterwards). The final test report is included with each HomeVision unit.

 

Conclusion

Although this is a long list, it doesn't even include our long-term product testing or customer Beta testing (That would take another article in itself!). As you can see, we've put a lot into making HomeVision reliable. We're so confident of HomeVision's reliability that it comes with a 3-year warranty (if you've seen the owner's manual that says it's 1-year, ignore it; it's really 3). Even so, no product is perfect. Hardware failures can occur, and software bugs are inevitable (just look at Intel's Pentium processor or Microsoft's Windows operating system - both are great products, but have dozens (and we're being kind) of known bugs, many of which they have no plans to fix). So if you should ever have a problem with HomeVision, please let us know and we'll fix it.

 

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Last updated:
09 March 2012

Copyright 1996-2012, all rights reserved, by:
Custom Solutions, Inc.
1705 Canterbury Drive, Indialantic, FL 32903

HomeVision is a registered trademark of Custom Solutions, Inc.