Tuesday, January 26, 2010

Stripboard magic

I have completed one of the constructional tasks on my list for this year, which was to make an interface between my Elecraft K3 and my 2m transverter so that I can leave the transverter on and it will only switch to transmit when I am actually on the 2m band. Up until now I have had to switch the transverter off if I change bands, which is not so good for frequency stability.

The circuit I used was given to me by Bill W4ZV on the Elecraft reflector. It combines the KEYOUT PTT control signal with the DIGOUT signal, both available on the K3's ACC socket. DIGOUT can be configured to go low only when a transverter band is selected. I only have one transverter, so that is good enough for me.

The combining is done using a dual opto-coupler TLP627-2. I'm not quite sure why an opto-coupler is needed, but as that is what the circuit said, that is what I used. The reason it took a while to get around to making this interface is that it was some time before I had a big enough list of parts to order from a source that sold the TLP627-2.

I built the circuit on a small piece of Veroboard. Prior to building it I thought I would design the layout using some stripboard layout software. Of course there was no need to use a layout program for such a simple circuit. But I have a more ambitious project in mind that I would like to do on Veroboard and I wanted something simple to try different programs out with.

I tried several programs, including VeeCAD, VeroDes, Stripboard Designer, Stripboard Magic and DIY Layout Creator. All of the programs to a greater or lesser extent suffer from a limited library of components, especially RF components like Toko coils or trimmer capacitors that you tend to use in RF projects. Therefore their usefulness depends a lot on the extent of the shortfall and how easy it is to add new components to the library.

The Java based DIY Layout Creator was quite impressive, and runs on Linux as well as Windows. However, adding components involves creating XML files containing the Javascript to draw the component.

My ageing brain struggles with complex tasks so I was attracted to the idea of programs that could generate a stripboard layout from a circuit diagram, or at least validate that the layout matches the circuit, because I am bound to make a mistake doing it manually. VeeCAD can check a layout using a circuit network description exported from a design program like TinyCAD. It can create a layout automatically but that feature is only available in the paid version so I couldn't test it. VeeCAD's component library is a bit limited and an annoying restriction is that you can't easily change the format of a resistor to mount it on end to save space.

Stripboard Magic is the only other one of the programs I mentioned that can generate a stripboard layout from a circuit. Its circuit designer is built-in and quite easy to use. The automatic layout generator seems a bit quirky, and produces a layout that may be electrically correct but seems to put the components all over the place. However you can add the components one at a time which gives you more control over the placement, and it will then check the layout against the circuit. Adding components doesn't seem too difficult and the library uses bitmaps for images so you could make them look realistic. Stripboard Magic is an old program that was written by a now defunct company but it is the one I like best at the moment.

I'm surprised I didn't find anything better for laying out circuits on Veroboard. I'd be interested to hear what methodology other constructors adopt when building circuits on stripboard.
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