Saturday, June 25, 2016

Copy and paste from one ExpressPCB file to another

[I have originally posted this to the PCB workshop FAQ.]

"Is it possible to copy and paste from one ExpressPCB file (schematic or layout) to another?"  I get this question once in a while.

Yes, copying and pasting between ExpressPCB files is possible.  It's just less intuitive, compared to what we are used to.  You can't open 2 separate instances of ExpressPCB and copy from one to another.  The workaround is to copy and paste within the same instance of ExpressPCB.
  1. Open the file which you want to copy from.
  2. Select the content that you want to copy, and copy it (press Ctrl+C).
  3. In the same instance of ExpressPCB open the file that you wan to copy to. (Or create a new file, to copy to.) It's important that you don't close this instance of ExpressPCB between copying and pasting.
  4. Paste the content (press Ctrl+V). The pasted content will remain selected. Move it to desired position. Done.
These steps were tested in version 7.3.5 of ExpressPCB and ExpressSCH.

Wednesday, May 4, 2016

Hacker Dojo had dumped its library. Alas, literally.

Dumpster in the Hacker Dojo's parking lot.
One of the Hacker Dojo's appeals was its library.  Unfortunately it got disposed of in the least sophisticated way.

There was a good number of classical books on engineering and software development there.  I've found Code Complete 2 and several Martin Fowler's books in Hacker Dojo's library.  I've added a few of my own books.  A few books I've put on my reading list, but didn't see them again (somebody got to them before me).
About a half of the dumpster is books from Hacker Dojo's library.
Other books were largely outdated.  Not many folks would want to read Flickr Hacks (2006) or Programming Windows 3.1 (1992).
I'm aware that a library is a bit of a white elephant, when it comes to moving.  Nevertheless, there were better options than a dumpster.
  • Post a message on Google group, Facebook, Twitter, and such.  There are people who love books and know what to do with them.  They could take them home, then bring them back to the new Hacker Dojo location.
  • There are plenty of ad hoc book exchange cabinets at local coffee shops.
  • Public libraries accept book donations.  They either add books to their inventory, or sell them.
  • Set the book shelves outside.  That gives folks some time to browse and pick out valuable ones.  That's still a smarter option than a dumpster.
I have picked out a trunkfull, and donated most of them to Redwood City library.  I'll read a couple first before donating.

By the way, during the previous move (from Whisman to Fairchild), the library was preserved.

Friday, January 29, 2016

Teardown of Fluke 52 II thermocouple thermometer

A small board responsible for cold-junction compensation (CJC) during thermocouple measurement is a curious part of this thermometer.  Have you ever designed cold-junction compensation for a thermocouple front end?  Let's see how Fluke did it.

Main board is visible.


Progressively removing the case. The cold-junction compensation board is not yet visible. It sits below the main board and behind the black plastic plate with slots for thermocouple connector blades.
The cold-junction compensation board sits below the main board.  The contact between the pads and thermocouple connector blades forms the cold junctions, which the instrument has to compensate for.  Since cold-junction compensation has its own daughter board, and it's somewhat  insulated from temperature gradients that may be generated by the main board.


Interestingly, the CJC board is made with metal (copper) substrate.  It promotes heat transfer and reduces temperature gradient between the cold junctions and the sensor which measures their temperature.  (The CJC temperature sensors are better visible on another photo below.)

Side view.

Thermocouple connector added to show where the contact between thermocouple materials and copper pads on the cold-junction compensation board takes place.

Cold-junction compensation sits on its own daughter board, and it's somewhat insulated from temperature gradients that may be generated by the main board. 

CJC board. Temperature sensors visible. Thermocouple plug added to the picture to show where blades make contact.
Main view of the cold-junction compensation board.
  • SOT-23-3 ICs between each pair of the thermocouple pads are the sensors which measure the cold-junction temperature.
  • An EEPROM (AT25010 ) suggests that the CJC board is calibrated separately from the main board and the coefficients are stored in this EEPROM.
  • LT1034 is a dual voltage reference

Each blade of a thermocouple plug has an individual spring clip that presses the blade to the contact pad on the board.

Related

Maxim App Note 4026  Implementing Cold-Junction Compensation in Thermocouple Applications
Discussion about cold-junction compensation in this Analog Dialogue article (2010).