Filter Airflow Display Mod

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Filter Airflow Display Mod

Postby glnc222 » July 25th, 2013, 3:12 pm

LED's in Vent Slot Indicate Filter Condition
ledstack.jpg
airflow indicating led's in vent slot


--connects to fan motor only, without opening top cover
--fits in vacuum compartment; standard headers can tap the lines without cutting wires
--indicates eight levels with four leds, lighting adjacent leds for midpoints
--measures fan power watts relative to the closed intake level, as per cent of a clean filter level
--indication between 80 per cent and 20 percent, interval of interest
--circuit requires no significant power for display

Based on measurements collected in thread "Electronic Filter Monitoring" http://www.robotreviews.com/chat/viewtopic.php?f=20&t=15981

While a regular vacuum increases fan speed and load when the intake is blocked, the constant RPM controlled Neato fan lowers power when less air is moved, requiring less current.

schematicairflow5.jpg

airflowboard2.jpg
approximately 1 x 2.5" 1/10" spaced perfboard holes

Technical detail of fan motor signals: the "smart" fan motor circuits inside the fan housing modulate current to maintain a speed set by the PWM input; the tachometer read-out is used by Neato only to determine when the fan is up to speed or whether the blades are obstructed. Current is a 16khz oscillating signal amplitude modulated, with constant 50 per cent duty cycle measured on a multimeter (at least at the Neato operating speed, 90 per cent of maximum settable over USB). The wave shape was not observed on a scope; any square wave input will be smeared by induction of the motor coils. Oscillation requires accounting for peak levels instead of average levels when amplifying.

This circuit measures the motor supply voltage lower than the battery voltage from semiconductor switching junction gaps. Similar measurements can still be made over USB reporting battery voltage and fan current.
Fan voltage falls over long periods from battery wear, but also from varied loads on the motor, and mostly from battery charge drop over a run (the fan does not slow over the run, increasing current draw to compensate).

An inexpensive IC is available which directly calculates wattage with analog multiplication, MAX4211, but is so small requires an expensive service to solder onto a prototyping adapter for one-off construction, with several shipping legs etc. The indirect method used here is much cheaper for hobby construction, and the limited application.


Inquire of any matter however simple.


Links to all Neato mods found for use in cleaning performance listed at http://www.robotreviews.com/chat/viewtopic.php?f=20&t=15981. Please notify of any omitted.
Last edited by glnc222 on August 7th, 2013, 10:49 pm, edited 4 times in total.
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Re: Filter Airflow Display Mod

Postby Osteo » July 27th, 2013, 10:01 am

Wow, this a a mod I might buy if the cost were low enough and the battery drain was negligible. I'm not proficient enough with a soldering iron to build a bread-board circuit but I can open, clean, and reassemble the beast so I should be able to add a simple circuit board. I'd really be interested if others used it and it performed as explained.

How much would you charge for this, glnc, or how much time did it take to build and how much in parts as I could estimate from there)?
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Re: Filter Airflow Display Mod

Postby glnc222 » July 27th, 2013, 2:02 pm

If you build this yourself the parts might run up to $25 depending on what is on hand, small bits by the dozen etc. I will contact you by PM regarding getting you one. In principle the company could just add this sort of function to the LCD display with a bit more software.
[edit] forgot you'd need a $40 multimeter -- instruments besides tools. And prototyped individual electronics costs several times mass production units, can't compete with commercially available products -- except when unavailable.
Discounts on out of stock items.
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Re: Filter Airflow Display Mod

Postby Osteo » July 31st, 2013, 9:36 pm

Thanks for the quick reply (even though this is delayed), got the PM and I'll get back to you on the weekend! Didn't want you to think I didn't get the msg. I do like this as I'm forever wondering if I should change the filter or just keep cleaning the one I'm using and I can see this being a comfort knowing the airflow is still good.
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Re: Filter Airflow Display Mod

Postby glnc222 » August 1st, 2013, 11:38 pm

Mechanical Alternative Filter Check

airflowtab.jpg
flap moved by sufficient Neato air flow only


A simple (and cheaper) alternative to the fancy electronics is a calibrated tab lifted by air flow when the filter is good, but remains down with insufficient air flow. Some people say they can feel the difference by hand.

The half inch cardboard strip shown just to the side of the charging contacts stays down with air flow at 30 per cent by the measures used and is strongly lifted at 65 per cent. Adding layers of tissue paper to a somewhat used filter allowed adjusting test air flow with USB readouts. There is very little air blowing out farther to the side than the position shown; the fan exhaust is in the middle and points straight out. Newer Neato's have an upward slanted exhaust behind the grate.

If the tab is hung on some paper clip wire from a block resting on the turret, down the support post so invisible to the laser, it can be put on the Neato when starting to check the filter and whisked off when the fan is up to speed to commence cleaning, or the Neato stopped for filter service. Vacuuming the filter restores much of the air flow until the point when the filter is finally worn out. Checks are needed only every so often.
[edit] actually the laser cannot see a thin wire if blackened. Also maybe a tiny bit of velcro instead.
[edit] could be permanently on and stowed flipped up into a paper catch on the upper half of the case, flipped down for use, hinge at the case joint. Paint to match the case. Whether gets scraped against walls not clear.

The electronics give a bit more precision and entertaining blinking lights.
It appears a printed circuit board for this project can be supplied by service firms in small quantities for around $12, but how hard it is to draw the necessary mask pattern with specialized software remains to be determined. Is it worth up to $60 to anyone? That can buy a lot of cardboard. Assembling one-off versions on perfboard is strictly for certified eccentrics, given how tight the spacing is etc.
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Re: Filter Airflow Display Mod

Postby glnc222 » August 3rd, 2013, 1:10 am

Cardboard Filter Check Tab Note
Might be permanently attached flipped up to a paper catch or tiny bit of velcro on the upper half of the case; lower when used. Paint to match the case.

LED's Across for Readability at Distance
Grating marks positions.

airflowacross2.jpg
airflow display led's across for readability

airflowacross3.jpg

A temporary wood block screwed to the back of the grate forms a platform for gluing led's to a plastic strip aligned in the slots. The strip is then braced by an unattached square dowel held by a #2 wood screw through a vent slot.
#30 wire wrap wires out to LED's under the exhaust grommet (not shown).

airflowcircuit.jpg
installed air flow display circuit


An small piece of thick foam weatherstrip is used between the fan and the board to secure against the side.

Would be a lot smaller if manufactured with surface mount parts etc.

Revised schematic is posted above, adding missing op amp resistors.
An inline 100ma fast blow fuse is also used on the fan power line connection for protection with hand made circuitry.
Last edited by glnc222 on August 6th, 2013, 4:20 pm, edited 1 time in total.
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Re: Filter Airflow Display Mod

Postby glnc222 » August 6th, 2013, 4:13 pm

Numerical Display

Just for completeness, at the opposite end of the spectrum from the cardboard tab, a small panel meter could be installed in the top with a 1/2 x 3/4" hole and show the measure used numerically as per cent. This meter is covered in "Worn Battery Indicator Light", similar size to "Neato With A Voltage Monitor". (The old circuit is not complete, with a two-stage amp in the present one required for oscillations.)

Only two dual op amp IC's are needed for a meter, omitting the three IC ladder of led drivers replaced by the panel meter, for a much smaller board fitting inside the case and more practical to wire by hand. More work then cutting the case hole for mounting, which could be done with a coping saw by hand for precision -- less forgiving of mistakes than circuit boards. Also inside the case 5v supply is already available eliminating the 5v regulator IC. The LED array is used to avoid opening the case and cutting it up. I kind of like it the way it is and don't need a more accurate display.

A numerical display could be switchable to multiple functions, with a small selector switch mounted in the rear grate or a small hole on top. But most things to measure seem related to servicing with USB so can be done with an external multimeter. The filter is something checked periodically so the LED display adds convenience without opening or modifying the case. Air flow has to be checked with the Neato running, so especially handy to have built in so visible during regular use.

PC Board Practical

Layout software of PCB service is quite advanced and does all the hard parts automatically, routing traces by itself. Would have to order three units I gather. Still not worth surface mounting with an assembly service as not that hard to make once a proper board is available for through-hole parts -- which still fit in the Neato.
Not that anyone needs these for something as mundane as replacing filters. A thing for gadget lovers.

tachometer line for memory

The tach return line from the fan (yellow I think) is a DC voltage rising to around 3v when up to speed. This can replace a timer if a record is to be made of insufficient air flow at the operating speed, maybe with just a single extra dual comparator configured as a latch, responding to both the tach level and the air flow level. Preserving the readout requires permanent 5v supply from inside the Neato or messy wires run to the battery compartment. The highest level LED runs direct on 5v, switched on the ground side, available for permanent lighting in addition to the transitory role. The bin-removed switch might be usable for resetting the permanent indicator latch, though there is room in the grate for a small tact switch, stem in the slots similar to the leds. There is a small opening at the corner of the vent grate fitting into the adjacent wheel well (where the plug for the exposed rear resistor is), and wires can fit around the wheel motor connection plug into the inside -- so no openings need be cut in the case though the cover must be opened, voiding warranties.

The point of recording is scheduled running unattended except every few days to empty the bin. A light on if the filter needs replacement, determined only when the fan is running, is then a convenience.

schematicairflowmem.jpg

schematicairflowmem3.jpg
better version resetting each start
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Re: Filter Airflow Display Mod

Postby glnc222 » August 13th, 2013, 2:53 pm

PC board economics
The kicker on the board-making service is a $7 spool of wire and a $7 wrap-and-strip tool at Radio Shack exceeds a share in three PC boards saving at least a day's work wiring by hand to boot. Soldering onto PC boards much faster as well. Haven't tried making a board yet though, needs some detailed parts sizes.
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Re: Filter Airflow Display Mod

Postby glnc222 » November 4th, 2013, 4:29 pm

inexpensive anemometer alternative
Image
A palm sized $10 fan anemometer reads as low as 70 ft/min, and was applied to the Neato exhaust.
Professional HVAC work uses precision solid state hotwire meters costing $200, for ducts etc. These cheap ones are adequate for home central air maintenance and a range covering Neato airflow around 1000ft/min (15 cufm) with a new original filter (more with Pet & Allergy). http://www.amazon.com/gp/product/B00840 ... UTF8&psc=1
Not good for hurricanes -- only goes to 60mph...
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