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Andrew Johnson's Blog

23 posts
This is part of my Instrument Control Board project in which I describe the choice of DAC, ADC and Op Amp. Component SelectionNo great science behind many of the components selected - mainly "do they do what I want?" and "price vs similar component".  So, for example, the choice of I2C isolator or Digital Isolator was really made around channels and required signal direction.  Confirmation of the chosen parts was made during the design to ensure (in my limited experience) they would su ...
Introduction jancumps, jc2048 and peteroakes are building an electronic load with what they call a Booster Pack control board to front end.  I've found it really interesting to look at what is being done and decided I wanted to have a go at something similar without just replicating what they have done.  I also wanted to have a go at playing with a DAC and ADC so it seemed like a good tie-in.  More specifically, these are the questions I'm asking myself: Could this be a generic c ...
I've been spending some time thinking about best using an ADC and I've done some weighing up of suitable components.  I've half settled on a Microchip MCP3248 rather than a TI ADS1115.  The Microchip has slightly better specs than the TI but it is limited in range on its inputs: -2.048V to +2.047V differential, 0V to +2.047V single ended; the TI has a more flexible option of ranges which expands its single-ended ranges, including a -4.096V to +4.096V, 0V to +4.096V single ended.   ...
The EDSAC rebuild team at The National Museum of Computing has posted a video about building some Nickel Delay Lines - you might be interested in watching.  Look out for the wonderful jigs that are built to facilitate the work - the museum is full of these types of things!     They are using Nickel Delay Lines because of the difficulty of using Mercury Delay Lines.  I love the whole idea of those things and I wrote a short article about them - for the TNMoC Members' Club - ...
andrewj

Call That a Relay?

Posted by andrewj Mar 3, 2020
This isn't meant to be an educational posting where you will learn a bunch of stuff about relays, but I've being doing some work recently that I thought might be of interest to some, particularly old-school engineers, to see how things change over time.   I would think we're all used to seeing modern relays that plug into breadboards and PCBs to switch signals.  I've opened one up, mostly, to see what's inside - mostly - I wanted it to still work after surgery!:   A 9V DPDT re ...
EDIT: 10/02/2020 - I've updated a couple of points in the text below following very informative comments received from other members. Introduction I’m taking the time to better understand how my scope is working and I was looking at its quoted performance specifications and how they translate into real life: marketing vs reality.  Turned into quite an informative activity so I thought I would write it up in case it can help any one else new to these tools.  This isn’t a rev ...
andrewj

Oooh.....Goody box.

Posted by andrewj Nov 27, 2019
Look what arrived today:   Could it possibly be...?   Yes!    It's a 10Kg/22lbs behemoth!  Now all I need to find is a UK power cable!   With many, many thanks to James, baldengineer, and Element 14.  It was awesome to get selected and this has definitely gone to a good home - I'm looking forward to putting it to good use.    Out of curiosity, and because I've not been able to do such a test yet, I thought I'd start off with a comparison ...
Selecting a CaseI need to fit most of this lot into a case   Aluminium, not too big and I want it to have some sort of decent aesthetic given it will sit on my desk for some time.   There are some very nice cases out there, mostly at an exorbitant price!  It’s not that easy to search them out either: forget eBay or Amazon as there is no way of filtering by size and I don’t have the patience to go through page after page of irrelevant entries.  I started out ...
Edit: 22/11/19 - updated navigation link   Following the rather disastrous last PCB update, I had it remade with a footprint that could take a 50uH inductor - and 10uH if I wanted to experiment.  Required a little jiggery pokery to fit the other parts around it but I also took the opportunity to rework some of the silk screen, layout, addition of a TVS on the input (D3) and re-size the mounting holes. It’s all soldered up and back to working again thank goodness - I’m s ...
Two things became very clear to me once I got into the detailed testing of the project: I have completely stuffed up the grounding and layout of the components.  In particular the Switching Regulator has a convoluted route back to Vin -ve and the route it does have takes it right under the sensitive components (until I bodged in a couple of wires).  Layout is too far apart for many components, including the bypass and decoupling caps, and non-conducive to managing noise.  There a ...
EDITS: 21/07/19 - added a PDF of the schematic             11/08/19 - updated navigation links   Introduction My intention was to document, in some detail, testing of the power supply with both a 10 Ohm and 5 Ohm load (to drive the current from 0A to 3A.)  To summarise, I’m seeing a number of problems - see later - and I thought I’d document where I’ve got to as I need to do some thinking about this.  See my ...
EDITS: 17/07/18 - updated links   It’s been some time since I last posted on this project because I’ve been busy with the museum and away for a few days.  It only took about 4 days to get the new PCBs manufactured and delivered from China, which is pretty amazing.  As it turns out, it was a bit of a blessing in disguise making the mistakes on the PCB as it gave me time to create the 4Duino interface which has proved very useful here.   I soldered up the Control ...
Edits: 15/6/19 - embedded YouTube video rather than just have a link.            9/7/19 - updated link to part 10   Whilst waiting for the new PCBs to be manufactured and delivered, I started on the Interface for monitoring the supply.  I prototyped this in Part Seven, so I know the fundamental code works.  To create the interface I want requires the use of 4D Systems Workshop 4 IDE so that I can make use of the graphical environ ...
EDITS:    14/6/19 - updated navigation link                27/6/19 - updated post for built power stage Prototyping Board I'm waiting for new PCBs to come before cracking on with this but whilst I'm waiting I will work on the 4Duino interface and I created this prototyping board.  The PCBs are the old ones (but don't change in size or appearance much).  I've kapton taped the switch as well as used hea ...
EDITS: 6/11/19 - Fixed broken links; Added link to Part Eight.   I'm going with an Arduino interface to display voltage, current, power and temperatures.  In the first version this will be display only - controls for setting voltage and current limits are manual (10 turn potentiometers) - but can be extended with more functionality in the future.   The 4Duino from 4D systems is an Arduino compatible (Leonardo I believe) device with a built in touch-enabled LCD, wifi and SD card ...