<div dir="ltr">Thanks Murray. Very helpful. I've ordered a brace of them. They're not in the Amazon store yet, so gotta wait on international shipping.</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Jun 8, 2021 at 4:18 PM Murray Altheim via DPRGlist <<a href="mailto:dprglist@lists.dprg.org">dprglist@lists.dprg.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi Karim,<br>
<br>
I'll try to get the post, which is about half ready, posted ASAP, though I've<br>
got a lot going on right now at home and work.<br>
<br>
I think it's definitely worth a look. My initial play with it was using the<br>
existing PMW3901 Python library, as suggested by the Pimoroni techs, and I'd<br>
tested it out over nine different surfaces and with that library I found the<br>
image complexity was clearly related to the measured velocity, but Pimoroni<br>
updated their library, and while the update doesn't entirely eliminate that<br>
issue, it's much less significant than before. I don't think you'll be able<br>
to use the sensor solely to measure distance over significantly varied<br>
surfaces with accuracy, but over a relatively constant surface I think it's<br>
pretty good, within a few percent.<br>
<br>
It outputs a simple stream of x,y values when moving, clearly on an interrupt<br>
basis as that stream stops when the movement stops. I measured the 'x'<br>
dimension (oriented as it was) over one meter and so long as I stayed on the<br>
kind of surface that I calibrated it for the measurements were quite accurate.<br>
An interesting notion might be to use the other axis with a PID controller to<br>
travel in a straight line, as while dragging my little robot sled over the<br>
test surface I'd get small 'y' values that could be used for course correction.<br>
<br>
With the new Python library I think the minimum to maximum of the nine<br>
surfaces I tested on (tile, wood floor, lawn, concrete, rug, etc.) varied by<br>
something like 10-15%, but on any given surface the ten runs of my test<br>
varied by only a few percent max, often less than 1%. Repeatable results.<br>
<br>
It'd be possible to calibrate the sensor over different surfaces and switch<br>
calibrations based on the surface if it were possible to detect the surface<br>
type, possibly using a camera or spectrometer sensor like the Pimoroni<br>
AS7262 that could detect color (which actually works pretty well, e.g.,<br>
it's easy in my house to know the difference between my tile, wood and<br>
carpet flooring by color). I've got a spreadsheet of results that will be<br>
part of the review/blog post.<br>
<br>
At £18.90 (US$26.75 / NZ$37) it's not cheap but I think worth a look, yes.<br>
The only downside really, which was entirely predictable, is that its<br>
operating range is 10-35mm, suitable for hanging underneath a small robot,<br>
but not so much under say, a Mars rover, whose bottom is likely higher than<br>
35mm. In that case the PWM3901 would be more suitable, but not necessarily<br>
as accurate,<br>
<br>
Cheers,<br>
<br>
Murray<br>
<br>
On 9/06/21 8:52 am, Karim Virani wrote:<br>
> How about at least a teaser? Worth a look?<br>
> <br>
> On Tue, Jun 8, 2021 at 3:49 PM Murray Altheim via DPRGlist <<a href="mailto:dprglist@lists.dprg.org" target="_blank">dprglist@lists.dprg.org</a> <mailto:<a href="mailto:dprglist@lists.dprg.org" target="_blank">dprglist@lists.dprg.org</a>>> wrote:<br>
> <br>
> Hi,<br>
> <br>
> FYI, Pimoroni has finally announced stock availability on their new PAA5100JE<br>
> Near Optical Flow Sensor, which I'll be posting a review on hopefully soon.<br>
> <br>
> PAA5100JE Near Optical Flow SPI Breakout<br>
> Detect motion of close-up surfaces with this Breakout Garden compatible<br>
> optical navigation breakout - great for floor tracking for ground dwelling robots!<br>
> <a href="https://shop.pimoroni.com/products/paa5100je-optical-tracking-spi-breakout" rel="noreferrer" target="_blank">https://shop.pimoroni.com/products/paa5100je-optical-tracking-spi-breakout</a> <<a href="https://shop.pimoroni.com/products/paa5100je-optical-tracking-spi-breakout" rel="noreferrer" target="_blank">https://shop.pimoroni.com/products/paa5100je-optical-tracking-spi-breakout</a>><br>
<br>
...........................................................................<br>
Murray Altheim <murray18 at altheim dot com> = = ===<br>
<a href="http://www.altheim.com/murray/" rel="noreferrer" target="_blank">http://www.altheim.com/murray/</a> === ===<br>
= = ===<br>
In the evening<br>
The rice leaves in the garden<br>
Rustle in the autumn wind<br>
That blows through my reed hut.<br>
-- Minamoto no Tsunenobu<br>
<br>
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