Some may have seen the post by another member venting frustration at not having an obsolete I.C. - a ULN3081. I read the post and investigated to find that this obsolete chip was really only 7 pretty standard transistors packaged into a chip case for convenience. I had an hour or so spare so I decided to knock up a PCB and make one so the member could try it out.
Short end to part one is that it has been 2 weeks now since I posted it from North Qld to Brisbane so who knows where it currently is???
Anyway, I decided to make another and document the process for those who might be interested.
Step one is to make up the PCB layout. Naturally we are constrained by first, the standard pinout of this 16 pin chip, and then by the physical size of 7 transistors. This is what I came up with:
OK - next step is to make a negative, expose some circuit board and etch and drill a board. I usually make a few at a time as it is just as easy (lucky in this case as the first was lost). After making the board & cutting it to size I like to tin plate them for ease of soldering and also longevity of the final item, I use a chemical tinning solution. I also use thinner PCB material for small items like this. It is harder to get and more expensive than standard 1/16" stuff but makes for a much nicer finished product. Here is the finished PCB ready to assemble.
Here are all the parts gathered together:
Time to cram on the discrete transistors - pretty close pads, so a close inspection after soldering to ensure no shorts between tracks and/or pads is in order:
Lucky I had already assembled a very crude test jig for testing this chip previously so it was a simple matter to plug it in and using the miniture switches I could check that the replacement I.C. functioned exactly as the original part would:
OK - that was a success so time to get the glue gun out to provide insulation and support & here is the finished item:
I added the paperwork and a turned pin socket as well as two strips of turned pins:
This time no chances with Aust Post - registered and ready to post Monday morning......
Hope I haven't bored too many
