Teardown of LG-1 light ring for Olympus Tough cameras

The LG-1 light ring picks up light from the LED, and guides it into a ring around the lens.  It uses the camera's LED light.  The LG-1 is a purely passive light guide, and it doesn't carry it's own light source.

Front view

Rear view

I question the function of the "pan handle" to left of the intake window for the LED light.  It's in a way of the flash.  The manual for the TG-5 says that the flash must be turned off when the LG-1 is attached.  It's painted white probably to reduce heating if the flash fires accidentally.  I might end up hacking off that [seemingly] unnecessary bit.

Rear cover removed

Rear cover with a window for LED light intake
(top)

Front cover with light guide
(center)

The clear part that does the actual light guiding

product page on the Olympus' web site:  LED light guide (LG-1) for TG-1/2/3/4/5

How to 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.

Hacker Dojo had dumped its library. Alas, literally.

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).

Other books were largely outdated.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.

Teardown of Fluke 52 II thermocouple thermometer

Have you ever designed cold-junction compensation (CJC) for a thermocouple front end?  Let's see how Fluke did it.  The point of interest in this thermometer is the small board responsible for CJC.

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. 

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).

I2C pull-up resistors on modules and breakout boards

I no longer maintain this page due to issues with SVG drawings on Blogspot.

The maintained copy of this page is here:
http://www.prolifictec.com/blog/2015/10/i2c-pull-up-resistors-on-modules-and-breakout-boards.html .

- Nick

 

Some of the modules and breakout boards for I²C slave devices contain I²C pull-up resistors. When multiple such modules are connected to the same I²C bus, their pull-up resistors appear in parallel.  That results in a stronger effective pull-up resistance, which may prevent communication on the I²C bus.

You have to have pull-ups on the I²C bus.

Somewhere on the  I²C bus you have to have pull-ups in order to be able to communicate on the I²C bus.  The pull-ups may reside on the microcontroller board, or on the I²C slave device's breakout board, or anywhere else on the I²C bus.

Some microcontrollers have internal pull-ups.  It's not recommended to use the microcontroller's internal pull-ups for I²C.  Still, internal pull-ups is much better than no pull-ups at all.

Watch out, though - you may end-up with pull-up that's too strong.

If pull-up resistors are too strong, that can prevent communication on the I²C bus.

Strong pull-up means that the current through the resistor is relatively large.  Stronger pull-up translates into smaller resistor value.  Weak  pull-up translates into a larger resistor value. 
(Stiff means the same as strong, when describing pull-up resistors.  This terminology is not limited to I²C.  It applies to pull-up and pull-down resistors in other types of circuits too.)



Suppose all three boards in this diagram came with pull-up resistors installed. The 2.2 kΩ value is common for an I²C bus running at +5V.  Notice however that R2, R4, R6 all are connected between SCL and Vdd.  They are in parallel, and they act as one 733 Ω resistor.  This combined pull-up is too strong I²C.  That can prevent communication on the I²C bus.  (Similar for the pull-up resistors on the SDA line.)

If these resistors can spoil the I²C bus, then why are they designed into the breakout boards in the first place?  I'm guessing that it must have been a compromise to create an easy out-of-the-box experience.  A lot of I²C first-timers don't know that pull-ups are required.  Some Arduino boards don't have I²C pull-up resistors nor pads for them (Arduino Uno, Arduino Pro, for example).  Some Arduino boards have unpopulated pads for I²C pull-up resistors (Arduino Mini Pro, for example).  A breakout board provides the pull-ups, and "it just works".  That is, until too many breakout boards are connected in parallel.

Remedies

Of course, as soon as you realize that there are extra pull-up resistors you can simply remove them.

Some breakout board suppliers are aware of the possible parallel pull-up scenario.  Many of the newer breakout boards have been designed with that in mind.

• Perhaps to partially address this, some of the breakout boards have I²C pull-ups which are half strength.  They are weaker than the correct values for the I²C, but stronger than the internal pull-ups of a μC.  A typical such value is 4.7 kΩ .  This is a compromise.  The number of modules that can be connected in parallel without removing resistors is still limited. But a greater number of modules may be connected before combined parallel pull-up becomes too strong.

• On some of the breakout boards, pull-up resistors are connected to Vcc through solder blobs.  A solder blob is easy to remove, then pull-up resistors will not affect the I²C bus.  (For example, see SJ1 in this SparkFun breakout board.)

• Some breakout boards have unpopulated pads for pull-ups.  (For example, see R1 and R2 on this board.)

Related

I²C bus specification and user manual.  Anyone working with I²C should at least skim through it.
How to deal with multiple pull-up resistors on modules?  That forum question was a point of departure for writing this post.
A case when ATmega's internal pull-ups were used for I²C.  The oscilloscope screenshots show I²C waveforms with internal pull-ups, and with proper external pull-up resistors.
Forum thread Is there a correct resistance value for I2C pull-up resistors? and application note I²C Bus Pullup Resistor Calculation.
EDN article Design calculations for robust I²C communications.  Concise article with diagrams showing I²C physical layer principles of operation.
Effects of varying I²C pull-up resistors.  The article shows oscilloscope screenshots of good and bad I²C signals.
Pull-up resistor and pull-down resistor explained

When does the Arduino Wire library actually transmit on the I2C bus ?

I wanted to better understand the inner workings of the Wire library (the I²C library that comes with Arduino IDE).  The detailed reference and source code were helpful.  To check my understanding, I made a simple oscilloscope experiment, which I would like to report in this post.

Setup

Straightforward test code, which creates a write transaction on the I²C bus.  To know when the calls to the Wire library methods happen, each one is preceded by a strobe on pin 13.  These strobes will be seen with an oscilloscope.   To know when the I²C activity actually occurs, SDA and SCL (the I²C data and clock lines) are too observed with the oscilloscope.

  void strobe() {

    digitalWrite(13, HIGH);           // Strobe for oscilloscope
    digitalWrite(13, LOW);

  }

  void loop() {

    strobe();
    Wire.beginTransmission(0x4C);     // Set the address of the target device  

                                      // which we want to write to

    strobe();
    Wire.write(0x07);                 // Payload: set the address of the register inside

                                      // of the external device, which we want to write to

    strobe();
    Wire.write(0x01);                 // Payload: value to write to the register

    strobe();
    Wire.endTransmission();           // Actually do the transmission.

    delay(1000);
  }

This code ran on Arduino LilyPad USB (my clone thereof).  It should work the same on any Arduino that's based on AVR and has got hardware I²C.

(The addressee of this I²C transaction is an MMA7660 accelerometer.  It could have been just about any I²C slave device.)

Results and discussion

As you can see, all of the I²C activity happens after all the calls to the Wire library methods have been made.
Wire.beginTransmission(...) doesn't actually begin the transmission, it only sets the I²C slave address for the forthcoming transmission.
Wire.write(...) doesn't actually transmit, it writes to a buffer in the Arduino's RAM.
Wire.endTransmission() actually causes the whole I²C transaction to happen from beginning to end.

Perhaps, the Wire Library functions could have names that better reflects inner workings.

References

[1]  Wire Library superficial reference
[2]  Wire Library detailed reference
[3]  Source code for Wire Library on GitHub

Teardown of Mastech MS8268 multimeter

The advertising for this multimeter stated that it has "warning when incorrect banana jacks are used relative to function switch setting".  I got curious about how the meter detected the banana plugs.  At first, I thought that there is an optical proximity sensors under each jacks, but that was an incorrect guess.  Each jack has a momentary switch at the bottom.  The switch has an plastic plunger, which insulates the detection switch from the banana contacts.

One of the light pipes, which forms the ring around a banana jack, is removed and shown separately on the right.
Red and black plastic parts inside of the banana jacks are the plungers which activate the detection switches.
The IC in the middle is a PIC microcontroller.  I suspect that it's main purpose is to detect leads, and to control the LEDs under the light pipes.

ICs in this meter, which I was able to identify

• Silan SC971.  Microcontroller.  Embedded A/D converter for DMM.
• Microchip PIC16F54.   Microcontroller.

I bought this MS8268 multimeter to measure low currents on the order of units of microamps.  The miltimeter didn't disappoint, considering especially a relatively low price.

Related

Mastech MS8268 review
Teardown video (Dec 15)