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:
Finishing this up
Well, now I have to wait until probably early next week to get my boards, funny that the shipping costs more than the boards themselves. I chose a fast shipment method this time around, as I am quite eager. Once I get them and admire them, and make sure I didn’t mess it up, it will be a snap to assemble. No annoying jumper wires all over the place and all safely and professionally made. Next up will be to slap it in a case I guess. I have all the parts for it that I want, though not a second voltmeter to monitor the input voltage, though that is not a huge concern. I’m thinking of re-using a case that I bad butchered for use as a speaker tester (it never worked well and I forgot how to use it anyway). It’s about the perfect size and will fit the meter, binding posts, three switches and the big adjustment knob. Difficulty is that I will have to replace the ruined front panel with something, I need a piece of steel or aluminium about the same size to make a nice front for it. Haven’t sorted that yet. I also haven’t sorted the front panel overlay, but I can make that up easily in illustrator.
How it runs
In a word: very well. In two words: foolproof. I’m actually surprised at how reliable it is. The meter will need some calibration adjustment, I think it’s about 40mV out from where it should be, but there’s a pot on the back I can adjust it with. The whole circuit, excluding the display which has its own supply, draws about 65mA with the fan going, and measly 5mA without it. Its power supply is rated for 200mA so plenty of headroom, could even whack in a more powerful fan if I find the little salvaged one insufficient. It handles voltage changes pretty much instantaneously (I’d need a DSO to actually see how well it deals with that, we’re talking switching times in fractions of a second, usually very small fractions). One of the things I absolutely love about this project is its sheer simplicity.
There’s always room for improvement. I’m rather limited in terms of what I can acquire and afford, so tightening it down into a precision, quality instrument is a bit difficult. With my faultymeter (yes, I call it that, not fond of Mastech) I can only measure so accurately, so calibration is kind of fuzzy. I am happy with the Dale 1% shunt resistor, but if I wanted to, I could get an even more precise shunt resistor to dial that measurement down. I could find a replacement for that crappy Velleman voltmeter. I have my eye on a 4.5 digit LED model from circuit specialists which I may order. That would mean I don’t have to switch ranges. It would be nice also to have a second meter for input voltage, but as I said, that’s optional. In truth, it’s accurate enough, and rock solid reliable, so there’s little I absolutely need to do to make this better. I may just assemble it as is and declare the project complete for the time being. I can always improve it later (and probably will).
Until then, I wait rather excitedly for my PCBs to arrive from Shenzhen.