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?