Month: October 2022

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FreeCAD and KiCAD workflow for Product Design

They are two software packages designed by two independent teams. Both of them are free to use.

To create a product you will need an enclosure that will house all the essential components inside it. And this enclosure can be built in FreeCAD.

I am using FreeCAD 0.20.1

There are some Addons that I have installed.

You can install Addon from “Tools > Addon Manager”

  1. KiCad StepUP workbench
  2. Glass
  3. PieMenu
  4. A2Plus (for making assembly from different individual parts)
  5. Fasteners Workbench (Easy to use the preconstructed model of many standard nuts, bolts, screws, washers, etc.)

KiCad StepUP workbench provides an ECAD-MCAD collaboration tool.

From what I learned in FreeCAD you create Sketch that can be exported to KiCad PCB.

The KiCad uses the Sketch created in the FreeCAD as Edge Cuts.

Edge Cuts are the outline of the PCB in which all your components along with all the tracks, via, hole, and other miscellaneous items must reside.

Youtube video from user mathcodeprint

This video demonstrates a basic example.

It is not a perfect collaborating tool. There are other software tools available from big companies but they are not affordable for a budding engineer.

The ECAD/MCAD collabration proccess:

  1. Design your schematic in Kicad.
  2. Assign Footprint and make sure that each footprint have a 3d model assigned to its footprint.
  3. make a pcb and update the component from the schematics.
    place a grid origin. Using the grid origin draw a rectangle in the edge cut layer.
  4. Save the pcb.
  5. After doing the above steps open the PCB in the FreeCAD KiCadStepUp workbench.
  6. Load the PCB into the freecad environment using the
    “ksu PushPull > Load Board” option
  7. Make changes to the sketch and the 3d model.

If you select a 3d model and make changes to its position.

To make changes to the 3d model. You have to select that particular model. And then you have to select the model from the Model view. Right click on the model in the Model view and select Transform.

Three orthogonal arrow will be preseneted to you in three different color.
You can move the model by selecting the conical arrow heads.

You have to push the changes by selecting that model into the kicad pcb.

After you have saved the kicad will automatically adust its footprint automatically.

It is this PUSH PULL method of making the changes to your pcb dimension and component positions.

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Standard Screws

Whenever you have to mount a pcb in place. Most of the time it is easier if we use the screws it on/in the enclosures.

There are standards for screws which are already available in the market. Which will reduce the BOM cost.

If you happen to calculate the screw dimensions based on the mechanical stresses. That would be the best. Since it gives you an optimum result in terms of material choice, strength and cost of the screw.

But in when you want to just mount the PCB on a plastic enclosure then you need to know the dimension in order to provide the provisions for the holes.

There are a few websites which will help in finding the appropriate size screw.

https://www.fasteners.eu/standards/ISO/

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MC34063 DC-DC Step-Down Voltage Regulator

MC34063 is an integrated circuit which has all the essential components to make a DC-DC switching voltage regulator.

There are other popular switching regulators in the market. And the mc34063 IC is not the very best. But this chip is cheap.

As you can see from the block diagram. This chip contains an AND gate, an SR latch, two transistors, A 1.25V reference voltage and an op-amp configured as a comparator.

You can just choose any value of the component and think they will work.

There are very basic calculations which you need to perform in sequential order. The calculations are given in the datasheet.

You need to calculate in this particular sequence only.

  1. ton/toff
  2. (ton + toff)
  3. toff
  4. ton
  5. CT
  6. Ipk(switch)
  7. Rsc
  8. L(min)
  9. Co

You can also take the help of an online calculator for mc34063

http://www.nomad.ee/micros/mc34063a/

or you can create a spreadsheet.

You must read the SLVA252B Application of the MC34063 Switching Regulator

By following you can create the cheapest switching power supply.

There are a few considerations with this integrated circuit.

There is a lot of switching noise. So you will need a bigger capacitor if you want to dampen those noise signals.

If you want to reduce the size of the inductor used. Then you will need to use a higher switching frequency.

You need to remember that the L(min) you have selected is for a particular base frequency. The maximum frequency will be set up according to the load connected to it. And the maximum frequency of the oscillator is 100KHz according to the datasheet.