Last week, I finally got a few parts I was waiting for. Namely the insulating pads that allow me to connect the MOSFET to the heatsink without making the entire case the drain! So with that, assembly is complete. Just need a label for the front which I can do at a later date if ever I make it to Staples to buy adhesive transparency sheets.
Properly mounted MOSFET. Note the pad under it, and the nylon bushing isolating the screw
It’s been a week of tweaking and assembly, mostly. This is both the part I love the most, and dread the most. On the one hand, it’s awesome to see the project come together and not just be a dangerous collection of bits on my bench. On the other hand – drilling into aluminium is such a chore!
Anyway, here it is thus far:
Front panel view, not perfect, needs labelling, but good enough!
As I said in my last post. I am mostly happy at how the Loaded Dummy performs, but with the caveat of some inaccurate voltmeter measurements.
After some more tuning and testing, I’ve identified two issues that leave the project just shy of my expectations. Neither are deal breakers, but are enough to make me want to investigate further and see if I could improve if not solve them.
Bit of a rats maze, but she works! All the bits are built.
For the past week and change, ever since getting my boards from the fab in the post, I’ve been assembling and testing and fiddling with my dummy load project. I outlined a few beginners mistakes in my last mention, and since, I’ve disovered a few more! Don’t worry, it still works fine enough and I’m still generally pleased with it. I’m even laughing at the absurdity of the bugs I’ve found.
Anyway, here’s the state of it now:
All the bits waving in the breeze, but she works!
Hurray! I got my PCBs via DHL this morning. So happy to receive them and hold in my hand my first professionally made PCB.
Well after humming and hawing, I finally just pushed the button on the dummy load project and ordered the PCBs from JLCPCB (via EasyEDA). I figured I can’t go too wrong, it seems most electronics youtubers seem to like it fine. I think the only thing that could go wrong is I made some mistake on the PCB layout, though I did check it over three times. You never know, Murphy might show up. Still, either way it will be a learning experience and if this works out (as it likely will) I will have more boards made up. I find this all very exciting!
Here is the layout I sent them:
Completely re-done from yesterday, includes the 12V supply
Now that I’ve got my Nixie clock all ready to be housed in a box, and lacking said box, I figured I’d motor ahead and try to get something else going. Next on the list is the Dummy Load, which has sat on a breadboard gathering dust for 3 years now. Funny thing is, I had figured it ready for assembly, but always good to check it out and see if improvements can be made.
To my surprise and delight, my design is working just fine.
Institutionalized Dumpster Dive
Over the weekend, I had occasion (in other words I made an occasion) to visit A1 parts and surplus in Etobicoke. I have mentioned it before as a candyland for the junk enthusiast and this is essentially correct. Despite its remote location, it is well worth the visit, just be prepared to dig and expect no help from the rather cantankerous guy at the counter. Total comic book guy for the electronics store which I find endearing rather than offensive. Anyway, if you ever end up there, be prepared to wade through tons of unsorted junk, find a few gems, and score a few surplus deals.
Or how I just love to overcomplicate things
Lights, buttons knobs and dials have always fascinated me. In fact, it says so in my baby book pretty much exactly. I think that was genesis of my love for technology, electronics, sci-fi and general science and nerdom. After all, what could be cooker then “techy shit” as gmunk puts it?
With every project I do, I tend to dream up ways of making the interface and functionality as flexible (read: complicated) as possible. I want to feel like I’m flying the frickin’ Enterprise when I do my thing.
Just a quick test and a quick solution
Had a few minutes to just check up on why the load would change when the voltage does. A simple test of trying a higher voltage power supply seemed to do the trick. Stayed within 10mA of where it should, and probably did better than that, but my multimeter can’t measure that. The new power supply is a 200mA 12V wall wort which is very unregulated. I measure 16V off the bugger with no load. Makes me wonder if what is printed on the box is merely a suggestion. Still, nice to have the headroom. Now the opamps have enough swing to really kick that MOSFET into regulating the current flow reliably.