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pkfox22-Dec-22 22:47

pkfox

22-Dec-22 22:47

Absolutely nothing for this Derek Sigh | :sigh:

Life should not be a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside in a cloud of smoke, thoroughly used up, totally worn out, and loudly proclaiming “Wow! What a Ride!" - Hunter S Thompson - RIP

yacCarsten22-Dec-22 23:05

yacCarsten

22-Dec-22 23:05

Sounds more like a contradiction in terms. Western music? relaxing? I don't think so. Big Grin | :-D

~~// TODO: Insert something here~~
Top ten reasons why I'm lazy
1.

OriginalGriff22-Dec-22 23:48

22-Dec-22 23:48

"What kind of music do you usually have here?"
"We got both kinds, we got country and western."
Big Grin | :-D

"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!

yacCarsten22-Dec-22 23:52

yacCarsten

22-Dec-22 23:52

It’s 106 miles to Chicago, we’ve got a full tank of gas, half a pack of cigarettes, it’s dark and we’re wearing sunglasses.

~~// TODO: Insert something here~~
Top ten reasons why I'm lazy
1.

Craig Robbins22-Dec-22 23:59

22-Dec-22 23:59

Hit it.

OriginalGriff23-Dec-22 0:16

23-Dec-22 0:16

"The use of unnecessary violence in the apprehension of the Blues Brothers has been approved."

Craig Robbins23-Dec-22 0:24

23-Dec-22 0:24

Pretty sure it isn't the answer, but John Denver is one of my favorite musical artists, and I loved the movie "Oh God".

Looking forward to seeing the real answer Smile | :)

DerekT-P23-Dec-22 1:04

DerekT-P

23-Dec-22 1:04

Definitely not even close, but thank you for participating! Big Grin | :-D

Telegraph marker posts ... nothing to do with IT
Phasmid email discussion group ... also nothing to do with IT
Beekeeping and honey site ... still nothing to do with IT

OriginalGriff23-Dec-22 1:33

23-Dec-22 1:33

I still got nothing ...

Craig Robbins23-Dec-22 1:49

23-Dec-22 1:49

I wonder... Could the first word be "wrap"?

OriginalGriff23-Dec-22 2:04

Re: WDNSO CCC OTD 23-Dec-2022 You win!

23-Dec-22 2:04

I guess we'll find out very soon - I think he's won!

OriginalGriff23-Dec-22 2:04

Re: WDNSO CCC OTD 23-Dec-2022 - edited with solution

23-Dec-22 2:04

So what was it? I got nothing ...

Craig Robbins23-Dec-22 2:32

Re: WDNSO CCC OTD 23-Dec-2022 - edited with solution

23-Dec-22 2:32

I thought of that answer Derek, but I could not make any connection between "artist" and a relaxing video. Guess I watch the wrong videos Smile | :)

DerekT-P23-Dec-22 2:55

DerekT-P

23-Dec-22 2:55

I think you get an "honourable mention" at least for that.

ASMR seemed to be a big thing a few years ago, maybe it's gone off the boil more recently. Never "got it" myself but had expected others to at least recall it and link to "relaxing videos" Sigh | :sigh:

Telegraph marker posts ... nothing to do with IT
Phasmid email discussion group ... also nothing to do with IT
Beekeeping and honey site ... still nothing to do with IT

Re: WDNSO CCC OTD 23-Dec-2022 - edited with solution

OriginalGriff23-Dec-22 2:34

Adventures in fan control

23-Dec-22 2:34

I guess that means you are up 3rd Jan, after Randow has had his go! Thumbs Up | :thumbsup:

honey the codewitch22-Dec-22 21:54

22-Dec-22 21:54

The hypothetical fan has a tach pin that pulses high twice per revolution.

There are two ways to get the RPM:

1. Count the actual pulses it makes in a minute and divide by two (or a fraction of a minute and factor accordingly)

2. Count the time (in microseconds probably) between pulses and use that to extrapolate the RPM. There are 6e+7 microseconds in a minute, so working with that, you divide it by twice the duration of the pulse.

2 has an obvious advantage in that it doesn't require you to sample for a significant period of time before you get a value. In fact, you can get a value each revolution since there are two pulses.

The problem with 2 is it doesn't work? My RPMs come back as like 5-7 on a 1700RPM fan being run at full power.

I've had other people eyeball my code and my math. There's nothing wrong with it.

So I've got some sort of theory of operation problem.

You'd think a fan would be relatively simple, but it stumped me.

To err is human. Fortune favors the monsters.

OriginalGriff22-Dec-22 22:01

22-Dec-22 22:01

Overflow?
Clock tick period? If this is shorter than you expected, you will get silly results if you try to time between two consecutive pulses.
If the rising edge isn't high / sharp enough, it could be triggering early or late?

But of course, sticking a scope probe on the pulse may change the results ... Big Grin | :-D

honey the codewitch22-Dec-22 22:08

22-Dec-22 22:08

I check the overflow condition by short circuiting with an early return if old_tick_us is greater than tick_us if that makes sense. In that case I just don't use that reading.

I've verified I'm getting the ticks because I've tried #1.

I've even tried taking a sample only every ten revolutions (20 ticks) and counting the duration between that and the initial tick and I don't get better results - can't remember what they were and I'm getting a friend's help to test since I don't currently have a power supply that can run a fan - one is on order.

Edit:

OriginalGriff wrote:
If the rising edge isn't high / sharp enough, it could be triggering early or late?

I missed this somehow when I first read your post. Interesting. The only thing that makes me doubt it is the RPM readings I'm getting are so bloody low - single digits when they should be four digits. It makes me think there's a deeper issue.

To err is human. Fortune favors the monsters.

Rich Leyshon22-Dec-22 23:03

Rich Leyshon

22-Dec-22 23:03

Not knowing what hardware you are using, just a thought that maybe irrelevant - but have you got any components (capacitors/inductors that in conjunction with resistors or internal resistance of other components) that may have accidentally created a filter that is tuned to roughly the frequency you would be expecting and either attenuating the signal or passing it to ground?

Maybe an idea to use an optical isolator to separate the output signal totally from the inductive load of the fan motor???

honey the codewitch22-Dec-22 23:24

22-Dec-22 23:24

I do share a ground with the fan but they are on a different power supply than the MCU that is taking the reading.

There aren't any components in the circuit other than a level shifter, which I know can handle these frequencies because I routinely use them with I²C devices.

Edit: I should add, I am getting all the ticks because method #1 in my original post works.

To err is human. Fortune favors the monsters.

CPallini22-Dec-22 23:26

CPallini

22-Dec-22 23:26

Can't you just output the duration between pulses, in order to discriminate between a measure error or computation error?

"In testa che avete, Signor di Ceprano?"
-- Rigoletto

honey the codewitch22-Dec-22 23:27

22-Dec-22 23:27

The only reason I haven't done that yet - admittedly part of it is laziness - is it complicates the code and I'm not sure what readings I should be expecting as I have no practical concept of a microsecond vs a spinning fan.

To err is human. Fortune favors the monsters.

CPallini22-Dec-22 23:40

CPallini

22-Dec-22 23:40

You should get about 18 msec for 1700 rpm (about 6 sec for 5 rpm).

"In testa che avete, Signor di Ceprano?"
-- Rigoletto