How to plan minor electronics projects

PLAN AS MUCH AS POSSIBLE ON PAPER BEFORE CONSTRUCTION Note that circuits in magazines often contain errors. Design it so that servicing will be easy. All part must be easily accessible. If possible check circuit operation using protype board construction. Ensure design is safely fused. Check that all components are available and at a price you can afford. Draw up metalwork and decide how the bits will be fitted together. Allow sufficient clearance between components. Give the front panel a pleasing appearance. Allow room for lettering on the front panel. Is there sufficient clearance between knobs on the front panel. Provide ventilation if necessary. Make all holes in the metalwork before bending. Ensure that it is possible to bend the shape you have designed. Plan transparencies for PCB's. Are heat sinks necessary? Heavy components must be fixed down. Use good component mounting techniques. Ensure components are easily removable. Strip insulation without nicking the wire. Tin flex without wicking. Single strand wire is more likely to snap than flex. Leave leads long enough to remove PCB's and examine both sides. Screen leads which carry very small signals. Keep inputs and outputs well separated. Keep cable forms clear of PCB's. Run them along edges and in corners. Use dissimilar colours for adjacent wires. Use grommets where leads pass through the chassis. Use good soldering techniques. See the shape of the joint through the solder. After soldering check position of components. Check orientation of IC's diodes, some capacitors, LED's and transistors. Use flux remover to clean board. Examine work with X6 magnifier. Spray boards with PCB varnish. When first switching on look out for smoke and flames!! If the project does not work then use a good logical approach to fault finding. Provide complete documentation. Parts list, circuit diagrams, description of operation, mechanical drawings,waveforms and voltages, and good fault finding algorithm. ENSURE ALL METALWORK IS EARTHED!!!

Last Updated on Tuesday, 10 March 2009 16:17

DRAW CIRCUIT DIAGRAMS

Written by Administrator

Tuesday, 10 March 2009 07:26

If you wish to draw some simple circuits, then use these symbols. If necessary, convert this drawccts.gif to your favourite format and use your art software. Just use edit, copy and paste. There are more symbols on another page, but these here are the most frequently used ones. If you can point me towards some more professional one, I would appreciate it.

USING STRIPBOARD

Written by Administrator

Tuesday, 10 March 2009 07:35

Tools required are a soft pencil and eraser, trackcutter, pliers, cutters, soldering iron and desoldering tool. Collect all the components required. Bend resistor, capacitor and diode leads to be about 0.1 inches long and at right-angles to the body. (note holes in board are 0.1 inch pitch). Extend the reach of components where necessary using wire links (22swg). Measure distance between leads and fatness of components. Convert circuit diagram to stripboard layout with a minimum of cut tracks and wire links (22 swg). Components will be on one side of the board, soldered joints the other. The power supply should be joined to the two outermost tracks. Keep inputs and outputs well away from each other. Try to keep all components at right angles to the tracks. Make provision to keep hot components clear of the board. Join tracks in parallel to carry high currents. Design it so that transistors fit three separate tracks. Cut tracks before soldering to avoid the track cutter digging into solder joints and ripping them up. Fit components so that they are flat on the board. Spring component leads out slightly to stop them falling out during soldering. Solder two diagonally opposite pins on I.C's and check the I.C's for flatness before soldering the rest of the pins. Solder one transistor lead and check that the transistor is vertical before soldering the other two. Cut off excess leads but do not cut the solder. IC pins do not require cutting. Upon completion check for correct values, correct direction of diodes etc, no solder splashes, tracks cut correctly, wire links present etc.

WIRE WRAPPING

Written by Administrator

Tuesday, 10 March 2009 07:45

Wirewrapping uses special wire wrapped around square pins. See Fig. 1 The corners of the pins dig into the wire, forming an airtight joint. Wirewrapping is quick and cheap. You can get lots of connections into a very small space. It withstands vibration well. Components are re-usable. However, it is difficult to make it look neat. Fig. 2 shows a regular wrap. Fig. 3 shows a modified wrap, where some of the insulation is wrapped around the pin. Modified wraps are more vibration proof. There are many types of tool available, from a few pounds, up to several hundreds. All usually have some means of stripping the correct length of insulation. Separate special wire stripping tools are available. When wrapping, push the wire all the way into the tool. Allow the tool to rise up the pin under its own steam.Don't pull or push it. Keep the tool on the pin until the wrap is complete. Avoid the following: Turns wrapped on top of other turns. Spaced out turns. Pigtails, where the end of the wire is not wrapped but sticks out. Loose wraps i.e not tight around the pin. Insufficient turns. Looking at Fig.4; if it is necessary to remove a bottom link then two upper links must be removed. If you have made wraps as in Fig.5 then you may have to remove ALL of your wrapping. PLAN AHEAD. Don't change levels.

HOW TO SOLDER

Written by Administrator

Tuesday, 10 March 2009 07:54

Use a damp sponge, frequently, to keep the bit clean. Tin the bit for good heat conduction.(This means putting a small blob of solder on the tip of the bit). Hold the iron like a pen. Rest your hands on the workbench to steady them. Take precautions against the work moving. (use a small vice or sticky tape). Heat the biggest part of the joint for 2-3 seconds. Apply solder to the joint not to the iron. Allow the solder to run over the joint without moving the iron. Remove the solder. Remove the iron. Avoid overheating.The process should take only 2-3 seconds. A dry joint is a poorly soldered one. A good joint is smooth and shiny. If the joint has moved during soldering it will be dull and crinkly. If you have taken too long it will have have solder spikes. The shape of the wire should be visible through the solder. All soldered joints should be easily removable.This means a minimum of lead wrapping. When using printed circuit boards avoid bending wires flat on the board. It makes them difficult to remove. Spring component leads out just slightly, to prevent them falling out during soldering. Mount components so that value markings are visible. Do not carry solder on the bit to the joint. The smoke you see is evaporating flux, which should normally clean the joint. Reflow soldering is tinning two pieces of wire separately and then reheating to join them together. There are some exercises on this web site. If you can do them well then your soldering is ok. REMEMBER PRACTICE MAKES PERFECT !!!