The proximity sensor cometh!

Having a night with nothing happening, I decided to finally move towards getting the proximity sensor on my printer. It's been lying around for a while (actually I burned one because the supposedly 12V power supply was actually 16V), and it's really the last thing missing on my printer. So onwards!

First thing I need is a voltage splitter so I can use the 12V signal in the 5V inputs on the Melzi board. Easy peasy, just two resistors and some jacks. That's what I have all this stuff lying around for. Solder it all up, and... find that I has placed the jacks wrong. Whoops. Remove, replace, resolder, not a problem. And then... find that the one resistor was 100Ω, not 100kΩ. Whoops. Remove, replace, resolder, not a problem. And then... notice that some of the soldering wasn't really that good and needed to be redone. Resolder, not a problem. And then I managed a simple circuit that should have taken 10 minutes but ended up taking more like 2 hours due to mistakes and misplaced things. Hopefully once my work table is in place the misplacings will be fewer. I don't expect they will ever stop.

The voltage splitter on the left, being tested. I like the little hooky test wires. 

With that prepared, I need to figure out exactly where to hook it up. The best information I have to go on is this thread on reprap.org, in which nophead as usual points out a number of subtle mistakes one can make with the most straight-forward approaches, though the solutions are not as obvious to me as they are to him. The "P" connections mentioned I'm already using for the e3d fan, but there's also four KRGB outlets (wait, is that a more colorful version of the Soviet-era secret intelligence agency?) that are not used. What do they do? Well, if I had done my fitting properly, they would have gone to the motor, but because the D connector was slightly off in the ribbon cable connection, I had to re-route those around the PCB. Thus those four are not used for anything, and I have no free connectors. Bother. Back to reading the specs.

Now the FAN+ pin has 12V on it, and would not be adversely affected by a bit more draw occasionally. But that's not connected to the ribbon cable. Wire 5 of the ribbon cable is unused and marked 'Probe', so that's probably a good one for the return signal. I suppose I can leech some 12V off the heater (HOTEND+), that won't disturb any readings, and for symmetry take GND from HOTEND- (or is there a reason it's HOTEND- and not GND?). So where is that Wire 5 going right now?

Here's the Melzi as it stands. There are three wires (#6, 7, and 8) going together into the second larger block, that's HOTEND+, and 3 more (9, 10, and 11) for HOTEND-. Wires 1 and 2 are the X stop, as can be seen from the red wires. 3 and 4 are for the thermistor. 5 and 12 go into the same block, the first larger one, with the top (12) marked as "FAN" on the cable, "FAN-" on the schematic. "FAN+" of the schematic isn't supposed to be wired to anything, and that's the wire 5 I could steal for signal.

My thinking is I can bring that one over to the contacts on the far side of the board. Whereas some builds show a 10-pin connector there, one mine it's just loose pins, free for the taking. Any of pins 2, 4, 6, and 8 (right row, from the top) on the lower section would go to EXT-A{1,2,3,4} on the chip.

On the top right: Pins enough to skewer a small mouse!

Not entirely sure about the HOTEND-. The schematic confuses me a bit. There's a HOTEND_BYPASS named JS2 that connects to ground through a resistor and that controls a power resistor. So that's probably how it's turned on and off. No, upon further inspection the HOTEND shown there is the connection. Slowly learning basic electronics here: that's an active low. In other words, no good for ground.

Having investigated these things, the original forum thread makes more sense. So I can take +12V from the heater, GND from the thermistor (though double-check if there's an influence on the reading), and bring the signal through wire 5. Great! Putting the appropriate connector on the voltage splitter and attaching it to the proximity sensor, it's all ready to go on.

By starting the hotend heating and measuring the voltage drop over it, I have determined that th right-most of the H sockets on the small PCB is HOTEND+ (12V), and the right-most of the T sockets is GND. But actually plugging them in will need to wait a bit. After spending about 15 minutes looking for a small enough screwdriver to unscrew Wire 5, I now need an even smaller one for unscrewing H and T. And it's late.

A Bullet Journaling template

Bullet Journaling! It's a thing! And it's a thing that Mickey and I have both had much success with (see my first post on the subject as well as several more on that blog). Mickey has switched to a weekly layout that suits her needs better, using a template we had lying around. This template unfortunately is long enough that it doesn't fit in the journal itself. So of course I took it upon myself to print a new one, also because it's a very simple thing to design. By making a module that does a generic "arrow" that can optionally have one outwards tip and one inwards tip, it was trivial to make this design:

A first print turned out to need enlargement because small features aren't that precise. More interestingly, the top layer was nice and flat in the large areas, but was over-extruded in the little parts between holes.

Between the parallel slats the edge is fine but the in-between is over-extruded due to going back and forth very quickly

I reduced the infill (at 50% from an earlier experiment) as well as the infill/perimeter overlap, but I suspect this is one of those things that requires changes to Slic3r, to adjust for very short back-and-forth lines.

For a second print, I also lowered the Z-offset a bit to avoid elephant foot that was closing up the slats. That was, of course, the wrong thing to do - it doesn't lower the plate, but the hotend, so I got even more elephant foot. Stomp!

The third print came out better, though still has some of the openings that should match a line distance not quite do so. Also, there's a huge blob in one of the slats. Anyway, it's just mere tweakings from now. The extra extrusion in the narrow parts is still there, but I'll just live with it.

A severe case of false economy

I haven't posted much recently, partly due to other priorities (fighting, and rearranging my work area), partly because in a bout of false economy I tried to use up the very last bit of a roll of filament and ended up running out before I noticed, and now the remainder is stuck. I've tried pushing it through with other filaments, with hex keys, and with tiny screwdrivers, with no luck. I tried taking photos through the filament hole to see if I could figure out the problem. I eventually took the entire hotend assembly off, so I could see the top of the E3D. There is the white filament, nicely stuck:

It's not easy to see the problem even here

Why is it so stuck? I presume that is due to the end of it getting either squished or ground or both in such a way that it doesn't quite fit in the narrow part of the the hotend. I had to take the cooling ribs off the hotend, then I could easily pull it through. Here's what the end looked like, clearly bent:

Once pulled out, the bend is clear

Putting it all together as always took a bit - it's a quite compact construction. I found a nice trick for the fan duct mount. It's always particularly tricky, since it mounts on two screws that don't have a lot of leeway - screw them out too far and they fall off their nut traps, and those are even harder to get back in place. Instead, screw them out sufficiently, then use a magnet to hold them out while putting in the duct. Easy peasy. Getting the filament pull idler also seems to be getting more and more difficult, not least because there isn't a proper backstop for the screws, so over time they dig further and further in - into the stepper motor, hopefully it can hold up to that.

Taken apart

Anyway, the printer now works as before: