Electronic Prototyping Tips
The E.E. Shop designs and builds custom test instruments and we've been assisting student projects for decades. Here are a few tips about prototyping your projects.
The greatest mistake students make with electronics projects is underestimating how much time it takes to produce a working project. It will probably take as much time to debug, fix, and/or redesign as it did to create it in the first place. Wiring mistakes, incorrect component selection, errors in the basic concept, and the need for unanticipated extra functions, all multiply the time requirement.
Account for ALL your pins. Besides power and ground connections, there may be chip enables, clocks, resets, and other similar inputs that have to be connected before things will work. Unconnected TTL logic inputs will "float high"; unconnected CMOS logic inputs can switch levels based on static charges or nearby signals. Logic inputs should be connected either to other signals, or connected to ground or the logic power supply.
Keep your wires SHORT. Long wires both pick up and radiate electrical noise.
White solderless breadboard connections are NEVER as good as soldered connections. Circuits featuring frequencies above a few megaHertz, or currents of an ampere or more, are not likely to be reliable on a solderless board. Breadboards tend to wear out with use, especially if you've tried to jam some fat component wires into the holes. This makes the connections even less reliable or may make some holes unusable. If you are having problems with your circuit, use an ohmmeter to make sure there really is continuity where you think there is.
Despike your chips. Power line spikes occur when there are sudden current changes far from the power supply, and this can result in unreliable operation. Putting a .01 to .1 uFd ceramic capacitor from the logic supply to ground right at the chip reduces this problem.
Make power supply and ground connections as robust as possible. A skinny, daisy-chained wire-wrap connection from chip to chip is probably not going to be enough.
Keep your digital and analog circuitry physically separate whenever you can. Digital switching, especially at microprocessor buss or video card speeds, can throw all sorts of noise and trash into analog or audio circuitry.
Silicon sealant or caulk is NOT AN INSULATOR. It will leak small currents, which may not matter in logic circuits but can wreak havoc in high-impedance analog circuits.
If you are intending to make several identical units, it's smart to finish and test one complete unit first. If you drill out all your cases, or make a pile of printed circuit boards, and THEN discover a problem, you've got to go back and fix or replace all the units. Get one right first, then duplicate it.
You may find an ideal integrated circuit or component for your design, but it may not be in production, or not in stock anywhere, or discontinued, or too costly. Check first.
Where possible, use IC sockets on prototypes. During the design/testing phase you need to be able to swap chips without repeated desoldering.
Data sheets from semiconductor manufacturers are your most valuable resource in creating designs, but they often provide crucial information in very brief, no-frills format. Some documents will explain device application at length and give examples, but not always. An absolutely critical detail about wiring or programming a chip may be mentioned only once in the text or on a chart: you need to read everything at least once and if you are having troubles you need to scour the information again.