More Boxy and USBee

Had some more fun with Boxy and my USBee analyzer. I’ve found a decent online supplier of aluminum at onlinemetals.com. (Now if only I could find one that takes bitcoin?) I got some 2″x1″ channel cut to 4″ long. The top of the electrical box is 2″x4″ and it fits nicely. I also got a lot of sizes and shapes of aluminum pieces, in part to justify the shipping expense, but also to experiment with other enclosures. I tested the channel on the target hotplate and it worked rather well, the surface of Boxy only got up to 35C. So this is nice because I can make the lid out of aluminum without scrounging up random pieces from my local electronics supply store. The aluminum lid is good because I can mount the triac and circuit board standoffs directly to the lid. Everything is flush and the triac enjoys a good thermal connection to the outside of the box. The flanges on the channel also make a decent enough heatsink, so I don’t have to add a separate heatsink and another thermal junction to the equation.Boxy powering an Aroma hotplate

I may need a better hotplate, however. This Aroma model I have got down to about a 65% duty cycle and the water wasn’t getting much hotter than 75C. This is hot enough for most sous vide recipes, but the spring controlled duty cycle ramping down to 2/3 will probably wreak havoc on the PD controller. 🙁 I’m thinking about giving the knob a setting, or adding a switch, that puts it at 100% always on. This worries me, though, for the housing of the hotplate was already getting above 100C, and the counter beneath got up to 60C.

Various pieces of extruded aluminum

Here I have the PulseView output of the zero-cross detect circuit in the boxy. The pulse width is about 900 microseconds, and the time from pulse leading edge to pulse leading edge was 8.3 milliseconds, which is close enough to 120Hz to chalk that up to eyeballing the measurement tickmarks error. PulseView has no ruler function, least of not all an automatic edge to edge time difference display. Oh well.

This is about 10% pulse on time. Assuming the pulse center is exact zero, that’s 5% cycle lead time, but cycle here is of course 180 degrees. sin(pi*0.05) = 0.15, so sampling at a rate where you would hit the worst case you would turn on the triac when the voltage is still at 15%. Of course you can over sample and count toward the middle of the pulse before switching. Just thought I’d throw that in there.

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