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General Category >> VeeCAD General Discussion >> 4 Pin Microswitches - TinyCAD / VeeCAD
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Message started by Stewart on Aug 7th, 2017 at 9:34am

Title: 4 Pin Microswitches - TinyCAD / VeeCAD
Post by Stewart on Aug 7th, 2017 at 9:34am
Hi,

I'm sure this is a solved problem, but I can't work out how!

I'm using the common 6 x 6 mm, 4 pin PCB mount microswitches in a project.  Pins 1 and 3 are common as are 2 & 4.

The problem is I can't get a netlist to recognise this and hence VeeCad want so put a break in the copper between pins 1/3 and 2/4.

I've tried various things in both TinyCad and VeeCad without success:

* VeeCad - using the same same pin numbers multiple times on the outline (modified TACT_01 package)

* TinyCad - adding hidden pins to the symbol with the same names as the visible pins. 

* TinyCad - as above but setting the pins to be power pins

I'm having to resort to manually editing the netlist!

Does anyone know the "proper" solution to this that doesn't involve having to expose 4 visible pins in the schematic?

thanks
Stewart

Title: Re: 4 Pin Microswitches - TinyCAD / VeeCAD
Post by Roger Lascelles on Aug 7th, 2017 at 12:39pm
Welcome to the forum Stewart!

I think you are referring to "tactile" switches.

There is a "Switch Tactile - Momentary, 4 solder pins" in the TinyCAD Passive library. That symbol has pins 1,2,3,4. To make VeeCAD understand that pins 1 & 3 are in the same net, you have to join them with a wire on your schematic.

The thing is, there are 4 pins on the real part, but you want to show only 2 on your schematic. Neither TinyCAD nor VeeCAD can handle that level of subtlety. And when I faultfind a circuit, I like the schematic to tell me where those 4 pins connect. For example, on some boards pins 1 & 3 act as a jumper between different nets. I think we are looking at the difference between schematic as manufacturing document, and schematic as presentation of concept.

Title: Re: 4 Pin Microswitches - TinyCAD / VeeCAD
Post by Stewart on Aug 7th, 2017 at 8:40pm
Thanks Roger,

You're right, I'm trying to keep the schematic "logical" and only worry about the physical in the package and VeeCad.

I've used the symbols you suggested, not the neatest solution, but it works.

cheers
Stewart

Title: Re: 4 Pin Microswitches - TinyCAD / VeeCAD
Post by Roger Lascelles on Aug 8th, 2017 at 10:19am
All the Schematic-PCB programs seem to hit a limit where something that is simple for human comprehension cannot be mapped onto the rigid model of the CAD system.

I think nothing should be hidden on the schematic. like hidden ground or power pins, because the information about which ground or power rail is then absent from the schematic. Thousands of board prototypes have been thrown out because of hidden information that was incorrect. Also because of duplicate pins.

I am happy to alter the schematic and reimport the netlist when I can see that my PCB or stripboard layout can be improved with a reallocation of pins or a gate swap.

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