Efficient Electronic Hardware [taken from C and the 8051]
- Use as few supply voltages as possible. With the right analog devices, a logic supply (usually 5V, but recently going as low as 2.7V) can often suffice. Microphone signals and most sensor signals never get that big. There is no law that all analog processing must be done with ±15V. Often, if the signal goes into an A-D converter and the signal-to-noise ratio is not a problem, it is unnecessary to amplify it to such levels.
- Use as little current as you safely can, and design so the high current drains are the shorter duration ones.
- For relays, pick the NO or NC contact that requires driving the relay the smaller part of the time. Of course, this is balanced by fail-safe considerations, but do not unnecessarily drive a relay 99% of the time to get a closed contact when you could use a NC configuration and drive it open only 1% of the time. Along the same line, if you are driving a solenoid, say to clamp off a hose most of the time, consider adding a spring, and have the solenoid pull against the spring to open the hose during the shorter open time.
- If quick access to replacement parts is important, focus on common devices found in local electronics supply houses—preferably with ready substitutes. You could use discrete transistor drivers for final output stages where the chance of failure is high due to abuse or other outside situations.
- On the other hand, now that most new designs rely on surface-mount technology, repairing most boards requires special skill and tools; stocking spare boards may be the best option.
- If you are designing a product for production and long life, wise customers may be concerned that parts may become unavailable—second-sourced devices are then a wise choice.
- Be conscious of temperature stability, but consider self-calibration to avoid requiring high-precision devices. Try to make all the accuracy of your design trace back to a single precision voltage reference or a crystal oscillator. Analog devices are inherently sensitive to inaccuracy and drift with temperature change. Unlike digital systems where noise below the logic threshold is reset to 0 or 1 at each stage, any noise acquired in an analog system continues down the path. The more stable an analog device, the more expensive it may be. If your system requires frequent calibration by setting potentiometers, they can be mis-adjusted as well. If the microcontroller can do its own calibration, the accuracy can be tied to a single stable precision reference voltage, for example, and the cost can be put into only one device.