2018. július 31., kedd

DIY Curve Tracer 3. - MCU selection

As I mentioned earlier I wanted to change the two AVR MCUs from the original design to a single 32bit one.
Here are my selection criteria:
  • Two at least 12bit DAC channel - One channel is used for the sine wave generation, the second maybe used for the pulse generation (not designed, decided yet, but better if it is available)
  • Two at least 12bit ADC channel - For measuring current and voltage on the DUT. If parallel sampling and/or differential input available is good but not requirement
  • DMA for DAC operation
  • 32 bit core - ARM Cortex-Mx prefered
  • Arduino framework support, free, native C/C++ IDE support (I haven't decided between the two, so the support is necessary)
  • Low cost development board
  • Easily solderable (for me. Means: TQFP accepted, QFN, BGA not - I know this is my personal limitation, but I don't want to learn it right now)
Based on the specs above my choice is an STM32F303RET6:

And the development board for it:

I ordered the board from Farnell yesterday. Today arrived:

Next: seting up the development environment

2018. július 29., vasárnap

DIY Curve Tracer 2. - Concept

Now, I'd like to summarize a few design concept for the project.
I started to work from the 3rd version. As I see now, It can be called as the 4th version because it will have so much differences.

  1. Modular design. I want to be able to use the design either with internal display or with an oscilloscope
  2. Use one 32 bit MCU instead of the current two 8 bit AVR (most probably an STM32)
  3. Internal power supply
  4. Based on the Huntron Tracker 3200S specification - except the 128bit scanning interface
  5. Complettely elliminate mechanical relays (even the reed ones)
  6. Get rid of the most of the digital potentiometers - not really fits for the needs, using resistors and analog MOSFET switches instead
  7. Get rid of the discrete R-2R DAC using an MCU integrated instead
  8. Utilize MCU integrated ADC/DAC/DMA as much as I can
  9. Get rid of the trimpots as I can (probably need to keep it for some offset setting functions)
  10. Keeping the error of the equipment around 1% every place (it is not a high precision equipment. If we want to decrease the error significantly, it cause significant rise in the costs)
  11. Adding the pulse generator as an optional module. It was missing from the 3rd version
  12. Adding the lower current limiting resistor ranges (down to 10 ohms)

First of all, I made a block diagram of the equipment:

2018. július 28., szombat

DIY Curve Tracer 1.

The things are never go the way I planed. A few month ago I put a poll on my blog about the next project. The winner is clearly the Home Automation Center. This thing I barely touched since, and now I'm completely in a Curve Tracer project.
I was visiting Peti Rácz's store/lab to ask him repairing my newly aquired tape recorder. We were talking about various things. He mentioned that he has an ancient Huntron Tracker what is very useful in repairing things. He would buy a newer model, but you can't get anything bellow $2000 (my opinion is this price is a simple robbery). I've checked the current model cost more than $6000 (are you out of your mind???).

I was strated to looking around if a cheap eBay/Aliexpress kit or a DIY project exists. Evaluating various options, finally found this project:
The owner of the project is also a Hungarian guy - Máté Tóth. Asked him to join to the project.
Now, I'm in. Let the journey begin.

2018. július 26., csütörtök

KiCAD 5.0.0

Just realized, that the KiCAD 5.0.0 arrived (four days ago).
The announcement can be read here:

It has some promising new features:
- New 3D modelling (the old was almost useless)
- Spice simulation
- Change in the Github based library management
Just to list my pain points.