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Frank Milburn's Blog

38 posts
I am developing an inexpensive but reasonably accurate meter for measuring resistance in the milliohm range.  The previous posts are listed in the related links at the bottom.  In this post the design for the working prototype is expanded to include a second current source for measuring resistance up to 400 ohm and provision made for future auto-ranging.  A new schematic and a PCB design are presented along with an update on meter options.   Revised Schematic The revised sche ...
I am developing an inexpensive but reasonably accurate meter for measuring resistance in the milliohm range.  The three previous posts are listed in the related links at the bottom of this post.  In this post a working prototype is presented that has milliohm accuracy down to one millivolt.  A schematic and test data are presented along with plans for the next steps.   Current Status That heading above is supposed to be a pun :-).  Much of the work since the last post ...
Introduction This is the third post on the development of an inexpensive but reasonably accurate meter for measuring resistance in the milliohm range. In the first post a simple current source was described that created a 10 mA current  across a resistor that allowed the voltage drop to be measured using a multimeter and the resistance calculated.  A number of helpful suggestions were received and I ordered additional components based on that feedback.  In the second post a block ...
Introduction In my last post I described a simple circuit that produced a reasonably accurate 10 mA current source to allow measurement of DC resistance down into the milliohm range.  I received  a number of helpful suggestions on how to improve the circuit as well as great discussion on selecting precision parts.  This post will outline several approaches I have considered on how to proceed.  As a refresher, here are the design objectives originally posted: Inexpensive Can ...
Introduction I was inspired by a recent post from shabaz on Building Kelvin (4-Wire) Test Leads.  Shabaz explains in detail and with clarity why measurement of small resistances with the two leads on a multimeter is difficult.  This got me to thinking about how I might build my own 4-wire Kelvin instrument.  This post will describe initial tests of a simple current source that can be used with a digital multimeter to more accurately measure small resistances.   Method and ...
In this blog I intend to outline a reasonably simple way to control Wi-Fi enabled Arduino compatible boards and single board computers like the Raspberry Pi or Beaglebone.  In addition an Apple or Android device that can run the Google Assistant app is needed.   Introduction   I have been thinking about this for a while and there are a number of approaches.  For example, two Ben Heck episodes Part 1 and Part 2  automated the workbench with voice control using Alexa. ...
UPDATED August 24, 2018 at the bottom of the post with parametric data at different voltages and gains   I have a project in mind that will require op amps and have been testing the Texas Instruments MSP430FR23xx microcontrollers with built in op amps. Yesterday I did initial tests with the MSP430FR2355 LaunchPad and looked at how gain can be set from inside the microcontroller.  The input voltage of 32.7 mV was very close to the lower rail  (the rails are GND and 3V3) with gain ...
As noted yesterday I have a project in mind that would use operational amplifiers.  Several manufacturers have microcontrollers with built in op amps and yesterday I took a quick look at the MSP430FR2311 from Texas Instruments.  Today will be a quick look at the larger and more powerful MSP430FR2355 which can be obtained on a LaunchPad.  This is a relatively new product and I bought my sample from the Texas Instruments store as it is not yet available from Newark / Element14.  ...
I have a project in mind that requires operational amplifiers.  Recently Texas Instruments has released several microcontrollers that have low power precision op amps built in.  I have two in hand now that I will be testing - the MSP430FR2311 that is in this post and the larger MSP430FR2355 that I may end up using in my project.  I won't describe the parts in detail today but instead will fire the FR2311 up in a kind of hello world for op amps.   The FR2311 microcontroller h ...
The Element14 community was kind enough to award me a prize in the Open Arduino contest and with the award I purchased one of the official displays for a Raspberry Pi.  I have wanted a portable marine traffic monitor for some time and this is what I came up with: It turned out quite nice, went together easily, and can be put together at a reasonable cost.  The project is a good demonstration of how powerful the Raspberry Pi is.   Components: Raspberry Pi 3 Model B Raspberry ...
Now that the TI-RSLK robot RoadTest is finished I have turned my attention back to a problem spotted in the last round of PCBs ordered for the AIS alarm project.  But first, I have a new toy. I have been looking for the right used Nikon microscope in budget but finally could not stand it any longer and bought this Chinese model after my friend bought one.  I am amazed at how much better this is than peering through a magnifying glass or loupe.  At low magnification stereoscopic ...
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ToorCamp

Posted by fmilburn Jun 25, 2018
I was able to attend an interesting "hacker" camp last week and thought it worth a post.  ToorCamp is advertised as "The Five Day, Open Air, Tech Camping Event where you create more than just ideas and build more than just inventions".  I don't think that is a particularly good description but I really enjoyed it.   It is located in the Orcas Islands which are located between Washington state in the U.S. and British Columbia in Canada, a very beautiful location.   Aroun ...
Project Objective: Develop an open source AIS Alarm that alerts sailors that a new marine vessel with AIS is within range   Project Update: In the last post I described the hardware state and showed a photo of the new boards.  This past week I have been testing the refactored firmware and chasing a bug that caused me to get out the logic analyzer. Logic Analyzer to the Rescue: When I refactored the code one of the changes was to the ring buffer which I described in an earlier post. ...
Project Objective: Develop an open source AIS Alarm that alerts sailors that a new marine vessel with AIS is within range   Project Update: In the last post I published a video of the completed prototype of the alarm and announced plans to continue working on the firmware and user interface.  In the meantime I ordered additional materials and today my friend and I cooked up a batch in his toaster oven. They turned out really tasty and I have the ingredients to make more :-) I've r ...
There is an active group of hardware / microcontroller enthusiasts that meet up monthly here in Seattle and I regularly attend.  Recently Scott Shawcroft who is a contract programmer for Adafruit attended the meeting and handed out the Adafruit Gemma M0 with Circuit Python to attendees.  This was a special edition that was made for PyCon 2018 with a custom silkscreen and I snagged one.  Here it is connected to a small Li-poly battery and shown next to an Arduino Uno to give scale: ...