Improved Current Load

Some Free Advice!

(Update - July 2019 - see the end of this post regards how not to blow this up!).

Back when I wrote about my failure to build a current limiting circuit for my Alarm Panel Interface, Zega was kind enough to offer me some advice.

Long story short, half the oscillations I was chasing in my limiting circuit were due to my quick and dirty Constant Current Load.  

Here's the Problem...

nrf51822 QFN48 Reference Design

Giving Back

The other day I was looking at my blog stats, I was surprised to find that my KiCAD posts were linked to, where someone was wanting help converting an Altium reference design into KiCAD.

So, I thought I'd help out - here's the reference designs, converted to KiCAD PCB.

Enjoy!

KiCAD Tidbits

KiCAD, For Profit!

I recently picked up a small contract for a board design, and the client wanted to use KiCAD.

I'd dabbled with KiCAD before, and even though I wont favour it over Altium, it's still a useful package, at a great price :)

But, it's not without it's quirks.

All About The Angles

Bright Light

The Workshop

At home I've seconded a small corner of my garage for my work space.  

You could describe it as 'spartan' or 'functional' but in reality, 'cheap' is more accurate.  One problem with the bench is that it's poorly lit.

Altium MultiChannel

Multi-Channel Rules

Just recently I was reading this post on the EEVBlog forum and thought "Ah ha!  I've done this before." Should be easy.  Famous last words.

So after spending a ridiculous amount of time workign out what the missing step was, I thought I'd better capture it for the next time I want to use it.

WHY MULTI-CHANNEL

You use a multi-channel design in Altium when you have multiples of an identical sub-circuit.  QAll you need to do is lay out the one channel, and then you can duplicate the layout by 'Copy Room Formats".  This has saved me a ton of time in the past.

THE PROBLEM

Altium uses a complex naming convention:

Multi Channel Meter, Part 2

From Idea to Implementation

What I really love about my hobby projects is that I can develop answers to questions that I can't explore at work.  20kW HF transmitters, Radar Installations all over the world, and Cutting Edge elemental analysers?
No worries.

Digitally Controlled Gain, Isolated PSU Choices?  Fergedaboudit.

In part 1, I detailed my path from the concept of a multi-channel volt meter, to a working system based on individual modules.  Here I'd like to talk about how I refined the design into my first prototype and then look at where I'm going from there.  Like Art, Engineering is never finished, you just chose a point to stop...

Multi Channel Meter

So after all that background...

Recently I've blogged about DIY Isolated Supplies and Microcontrolled Analogue Gain, as these have been necessary building blocks for my latest project - a multi channel voltage / current meter.

Microcontrolled Analogue Gain

Digital Controlled Gain

For a long time I've wanted to implement a gain stage where I was able to alter the gain under digital control.

Why?

Back in my Uni days, I have to build an Automatic Gain Control circuit, and was greatly dissapointed that the trick there wasn't variable GAIN but variable ATTENUATION on the front end.  At the end of the day, that approach works well where i used it, but I always wanted to have true programmable gain.

But this was the case of a solution looking for a problem, until I decided that I wanted to build some test equipment that required programmable gain!  So, to test the theory I cooked up this:

It Worked!  Eventually!

Upcoming

Coming Soon

I know I've been a touch quiet on the blog, mostly because I've been sidelined with other projects.

Blog entries for all coming but here's some preview pics:

Multi Channel Meter

Isolation Options

Isolated PSU

So if you find out you need to isolate your circuit, you will need to power it over the isolation barrier, and there are options out there to do that.

Finding myself in that position, and being a notorious tight-arse I started to look at DIY options.

10 Years On

DIY Trailer LED Lights

About 10 years ago I built a pair of LED trailer lamps for my Father In Law. This was back when LED lights were stupidly expensive - and as luck would have it I had access to some high brightness samples. 

Anyway, the lights served their time in the harsh conditions of the Riverland and the plastic lenses finally turned more opaque than useful. 

After replacing with a set of lamps off eBay for less than $40 I thought I'd share what they look like now. 

Keeping Things Isolated

Why Use Isolated Power Supplies

With most hobby electronics, all your system parts tend to operate from a common ground.  This makes things easy to understand, as you just measure what a device is 'doing' with respect to ground, and you can make things happen in your design.

For example, you can decide that 5V above ground is logic high, and if your micro sees that level on a pin ou can turn on a light. Or if it's an analogue value of 3.2 volts you might think your room is warm enough and decide to turn off your heater.

Sometimes you might here this referred to as an 'absolute value' above ground.

Makes sense.

But sometimes, you don't want to know what the difference is between two points that are different to ground.

Huh?

More on Alarm Panel Interfacing

I've Been Busy...

I haven't had the chance to update things for a while, but for those interested, I'd like to share some build pictures of my Alarm Interface.  And yes, it's working and in service, with a nice programming GUI. (Links at the end - code will be up "soon").

Teaser Render!

Measure Twice, Cut Once, Get a New Ruler....

History Repeats

With past projects, I've made some mistakes that are common to a lot of projects.  Who hasn't mixed up D+ and D- on a 485 driver?

One thing I've added to my workflow is using excel to help build my new packages.  In Altium you can copy pin information from a pdf into a table, massage it as needed and then pate it onto Altium.  I've configured 100 pin devices like this in a lot less time it would take to edit them one by one.

Closing the KiCAD Gaps

Imports and Persistence

As discussed before, I'd decided to try KiCAD for the first time and the approach I took as to port an existing design, in this case EEVBlog's uCurrent.

To recap, I'd produce a schematic that still needed it's annotation and part values updated, and I'd also imported the Altium PCB files into KiCAD, with an Altium to P-CAD conversion as an intermediate step.

New Boards!

New Boards

My next bunch of boards from Seeed studio have arrived.  Here's some shots of parting out the prototypes from 10 x 15 cm panels.

Build and test info coming... as soon as I build and test.

What's All This KiCAD Stuff, Anyhow?

Going Open Source CAD

As can be seem from various post's here, I'm an Altium user.  I'm lucky enough to have access to it work, and I've been using it since it was good old Autotrax for DOS.   Yes, I'm that old....

For work that's fine but with my home projects I'm keen on sharing these as Open Source Hardware and releasing designs in Altium goes against the grain here - the community prefers that you share using open source tools.

So with this in mind, I decided to take the plunge and try KiCAD.  My following thoughts will be comparisons between 'what I know' about Altium and what my impression are about KiCAD and I fear it will be far from fair.  Altium does set the bar, and thus my expectations of what a PCB CAD tool can do, pretty high...

It Can Be Done!

And besides, I need something to do while I wait for my next revision of Alarm PCBs to land....

Getting one up on the kids!

Free Stuff!

Over at the EEVBlog forum a PCB Fab house by the name of JAKO made an offer - FREE 5x5 cm PCB Service.

Woot!