Drip Governor - A most valuble first hack

[BrockMcKean]

EDIT: I just realized that Rylan has already taken pretty much all of this into account save specifics of electrical and programmatic operation, so perhaps we should focus on that. :S

Brock McKean: I think that while it would be possible to use frequency modulation (or other techniques discussed in this forum) to directly control the drip speed with the speaker, in my opinion this is not the way to go. I think that having the speaker control the laser as well as possible should be the priority. Adding a bunch of complexity (or greatly limiting the drip governor's functionality) to save one or two dollars does not make much sense to me.

If the point is to keep the cost as low as possible and it's reasonable to do something that would decrease the cost I don't see why it shouldn't be done. If the mirrors truly operate on AM, FM should not affect them at all. But if we did want to add a filter before it, it would guarantee that no FM would ever reach the laser assembly. Adding somethign like that will cost basically nothing, pennies. Placing a low pass filter before the peachy's mirror/coils would completely isolate it. Using an op-amp to, connected to the 5V for DC bias, and passing the frequency from the audio jack, the coil can be controlled directly. I guess it sounds a little complicated, but I assure you things like this (using multiple and separate modulation schema) are done all the time in many electronic devices.

Since when the valve is open liquid rushes through fast I think that there is not a need to have it stay open when the coil is not powered. The coil will only be powered for a tiny fraction of a second anyway.

Yes, I agree. It shouldn't stay open. This means we need a switch between 5V DC and Ground, or some way of using the AC signal directly from the audio output that will result in the desired movement. Maybe we can use PWM over USB instead if we are going to use it for a DC bias directly from the device anyway. This would probably be easier and certainly separate if it can be achieved at the correct voltage/current level on the data line USB data line.

As for maintaining the orientation of the magnet this happens naturally, so no extra work is needed. The field makes the magnet's orientation stable.

Unless the magnetic field is on the entire time and the desecent of the magnet is forced and controlled, there's no way to guarantee that freefall will not result in the magnet ending up lop-sided, assuming there is pressure above the magnet still. However, if it has some sort of guiding rod to prevent it from turning to that kind of angle that extends from the magnet up/down the drip a bit it should be no problem.

There is something about the pressure worth thinking about though. This valve should be placed as high up as possible to minimize the pressure and hence the magnetism needed.

Yes, but then you also have to worry about the reservoir's resin level. I'm not really sure how the drip works now exactly (at all really), but any resin below the valve would have to be pumped to the valve somehow or the reservoir would have to mechanically change to deliver the resin. So if this is not a problem it should be placed as high as possible.

I don't think that spectacular accuracy is needed here though because that will be provided by the water level measuring methods.

If the drip governor can only move to one position we're limited to altering the period for variability, which is fine and probably the best approach. However, the dynamic range will then be determined by the minimum amount of time we can open the valve. Accuracy is not a problem here, but if we want to be economical about it, the software should take the drips into account and calculate the resin level without measuring afterwards (because the drip resolution and number of drips are known, the entire volume is known). This would require using a well defined right rectangular prism as a reservoir (all opposing sides parallel, all adjacent sides perpendicular) so that the area for each level is identical. I'm not sure if that's part of the peachy's design right now or not to use some sort of level measuring method, but calculating it this way would be much less invasive and not disturb the print surface/material in any way and would allow for more printable volume.