Wednesday, January 25, 2017

Accessories and peripherals time!

Part of any good system is the amount of expansion that it offers. As I'm building my own components, I can build in as much expansion as I want.

As most of my components are going to run on 1-wire or powered I2C, I chose to go with the venerable modular jack for an expansion interface - in this case, the "5222" 6P6C style connector. They're common enough that you can buy them bulk for a few dollars on the web.

Since boards are so cheap, I've laid out my own board. 6 "5222" connectors, with the capability to add both power and a DS1820 sensor (if using 1-wire systems.) Otherwise, the DS1820 can be omitted. There's some minor power filtering on the board, and the 1-oz copper should handle 800mA or so with no issues. Anything more than that would be cabled direct anyway.

The top of the board offers the I/O connectors, an LED for any power that may be supplied, and a spot for a DS1820 sensor. Currently, I'm using AVTech Room Alert devices, and this board's DS1820 sensor is wired to follow their color code. That's completely optional for other devices. There's also a pullup resistor wired into the Data/VCC lines. There's a lot of discussion on the necessity of this, but it's there. Just in case...

The bottom has the filtering for the power and the resistors for the LED and pullup. A IPC-7351\Chip-CaseC capacitor for ripple smoothing and a single 0805 for high-frequency noise reduction. All mount holes are ground plane.

The boards are shared on OSHPark, feel free to use them.

There's not a whole lot going on, but I can make these by the dozen and drop them in where needed.

5222 "6P4C" connectors. Just remember the pin numbers are different than a 6P6C!

Wednesday, January 18, 2017

Testing the precision rectifier circuit...are those parts marked right?

My boards came back from OSHPark late yesterday afternoon, so I went ahead and built one up this morning. Most of the parts came from new stock or the shop's parts inventory, but the diodes did not - germanium diodes are easy to get if you buy packs of surplus Soviet parts on eBay, but buyer beware!

As with the other boards I've purchased from OSHPark, all the text was nice and clear, holes were clear, and the solderability of the board was excellent. It went together quickly and easily.

(In retrospect, I should have noticed the diodes weren't right, but I haven't worked with Ge diodes for so long...)

Some quick checks on the board revealed that I had made a stupid wiring error. The input voltage was reversed. I have no idea why, other than I just didn't run the traces correctly. That was a simple fix, cut a track and run a couple of jumpers. After that, it came right up, all LEDs lit and no smoke!

Second issue was the LEDs are drawing way too much current. While 20mA isn't much, I want to keep the total draw down as much as possible, so I'm going to increase the current limiting resistors to 4.7k. I need them lit, not lighting up the inside of the box.

So, those problems are taken care of, and I've got it hooked into the electrical system here at the shop for testing, but it's not acting like I think it should. Everything is floating around way too much, and the outputs are going negative...

That shouldn't happen. I immediately suspect the diodes.

Off to the bench, a quick meter check reveals that the bands on the diodes are actually on the anode! Looking closer, I can see the point contact to the Ge is under the bands. Go figure! (Someone mentioned that it was marked like a selenium device...)

Here's a closeup, and you can see the cup with the wire coming out, and just make out the semiconductor material under the bands. What I find odd about this whole thing is I've seen other examples of this diode, and they were marked correctly. Oh well, now I know.

(The Russian D9E, or so the package says!)

With the diodes in correctly, it goes back to the test rig. Now, everything is working just as it should!

Perfect. The output jumps when my device activates!

The current transformers are just clipped on to the input to the box. I'm not worried about how much, just the absence or presence of current in this case. Calibration will come when the devices are secured and can't move around.

This test is successful. Time to button up the panel and get ready to build one for myself, and think about where things are going to be installed.

Wednesday, January 4, 2017

The energy monitor begins to take shape.

One of the interesting things the CAI board offers is some analog 10V inputs - DC of course, but this is perfect for getting some sort of data back into the system. It just so happens the clips I purchased for the energy monitor work in this range, so...we're back on!

First thing is to wrap up the board necessary to get the voltage off the current clip and into the system. Since I'm also designing a similar project for my employer, that was easy enough, and an order from OSHPark later, I have a board getting ready to be spun up (and partially paid for by said employer!)

This is the same precision rectifier circuit that I was working with last month, except the board is now laid out, a power converter chosen ( the EC3SA-12D05N from ) and other parts ordered.

Other than the power converter, it's pretty old-school. TL084 op-amps and germanium diodes, chosen for their low voltage drop. If you want to order a set of boards for yourself, the project is shared on OSHPark's website, but I would suggest waiting until I can verify I didn't do something stupid, and can get a parts list together.

I should have them in about 2 weeks. Until then...