PSU Console

Dead Simple Power Supply

At work I'm quite spoilt, there is an abundance of equipment in the labs, and if I need, I can borrow something for home use.  Very handy when ding something specific (like the thermocouple I used here) but it comes with a down side.

If I realise I need something, it means dropping work for a few days until I can borrow the equipment (if it's in use at work, I can't have it until it's free) and as I catch the train, it also means bringing the car in if it's too big to fit in my backpack.

When it came to powering my projects, I have a very basic dual rail Power Supply (I built one just like in in Uni, tortured it to death over the coming years by running a car amp from it in my bedroom) that I inherited from a guy-who-got-it-from-a-guy-from-a-garage-sale deal.

The updside: It's got dual isolated rails, 1.25V to 15V range and 'up to' 1A output.  

The downside: It's so old the pots are scratchy, so setting an output voltage is a chore, and there isn't any current limit.  And you need to whip out your multimeter to set the voltage / measure the current in use.

So I got cracking on this:

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!

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.

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?