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Topic: Car reverse backing obstacle sensor with sonic ranger (Read 8 times) previous topic - next topic

retrolefty

Ok, then on to your next auto project. How about a arduino low tire pressure alarm? My 11 year old Buick has one built in, tells me to check tire pressure.

Lefty

liudr


Ok, then on to your next auto project. How about a arduino low tire pressure alarm? My 11 year old Buick has one built in, tells me to check tire pressure.

Lefty


I'd like that too! I don't have a pressure gauge. The cheap ones all fell apart on me. How do you sense pressure? I know pressure capsules with voltage output but how do you do that on a rotating part? Now i have an idea. Put my persistence of vision display on my wheel so the dude driving next to me can honk me if he sees the message: "This dude needs more air on this tire!"  XD

mmcp42: I can certainly do that. It won't help me backing blindfolded though! :smiley-mr-green:

retrolefty

Quote
I'd like that too! I don't have a pressure gauge. The cheap ones all fell apart on me. How do you sense pressure? I know pressure capsules with voltage output but how do you do that on a rotating part? Now i have an idea. Put my persistence of vision display on my wheel so the dude driving next to me can honk me if he sees the message: "This dude needs more air on this tire!" 


This will be fun. I will only give you hints and additional hints if asked. The Buick has NO pressure sensors used to determine the low pressure warning. Also it does not tell me which tire is low, just that one needs attention. So how might you think it can determine that?

Lefty

mmcp42

I'm guessing:
a) level sensor, if one side is low chances are the tyre (sp) is flat
b) rpm sensor, if one wheel is going "faster" it's got a smaller (effective) diameter, so the tyre is flat

a) is very hard to measure accurately
b) has to take cornering into account
there are only 10 types of people
them that understands binary
and them that doesn't

liudr

Lefty,

Since you challenged me to figure this out, I'll have to ask:

1) if you deflate all tires equally from equally well pressurized initial condition, will your old Buick still tell you low pressure?  :smiley-roll:
2) if you deflate just the front tires but equally, with you get a low pressure warning?
3) if you park your tire-well-pressured old Buick on a slope (Should be plenty in SF, right?), with its side doors facing the top of the slope, will you get low pressure warning?
4) if for some reason you're driving your old Buick and it reports to you tire pressure is low, will stopping the car turn off the warning?

I'm thinking about a bubble level (or tilt sensor) running under the car from left to right but if you carry out the above thought experiment and get back to me, I can be more or less certain about my guess.

BTW, I was not googling anything.

retrolefty


Lefty,

Since you challenged me to figure this out, I'll have to ask:

1) if you deflate all tires equally from equally well pressurized initial condition, will your old Buick still tell you low pressure?  :smiley-roll:

I don't think so, but I haven't tested that.

2) if you deflate just the front tires but equally, with you get a low pressure warning?

I think so, but i haven't test that.

3) if you park your tire-well-pressured old Buick on a slope (Should be plenty in SF, right?), with its side doors facing the top of the slope, will you get low pressure warning?

No, it seems to take some time averaging before it issues a warning after actually driving some distance.

4) if for some reason you're driving your old Buick and it reports to you tire pressure is low, will stopping the car turn off the warning?

Only if I turn off everything and pull the key out. Warnings can also be reset, but will return if still true, like low oil level, time to change oil, door ajar, etc.

I'm thinking about a bubble level (or tilt sensor) running under the car from left to right but if you carry out the above thought experiment and get back to me, I can be more or less certain about my guess.

No car has to have travels some distance before tire pressure warning is issued.
BTW, I was not googling anything.

Funny, after I first got the Buick I goggled and did fine the method used for my car.

retrolefty


I'm guessing:
a) level sensor, if one side is low chances are the tyre (sp) is flat

No level sensor involved.

b) rpm sensor, if one wheel is going "faster" it's got a smaller (effective) diameter, so the tyre is flat

You are getting very very warm here. However I will confuse and challenge that it doesn't use a sensor just dedicated to tire pressure warning.

a) is very hard to measure accurately
b) has to take cornering into account

I don't think cornering is a factor. It's not an alarm that comes on instantly, it takes some distance traveled.

mmcp42

well if it's just the rear(driven) wheels you could spot the differential gear turning
OR
if the car has ABS there could be an output from the speed sensors...
there are only 10 types of people
them that understands binary
and them that doesn't

retrolefty

#23
Feb 16, 2011, 09:40 pm Last Edit: Feb 16, 2011, 09:42 pm by retrolefty Reason: 1

well if it's just the rear(driven) wheels you could spot the differential gear turning
OR
if the car has ABS there could be an output from the speed sensors...


Quote
if the car has ABS there could be an output from the speed sensors...


Give the man a cigar. Antilock Braking Systems have a sensor to tell if a wheel is turning or not so as to release brake pressure on a 'lock-up' wheel during a breaking situation. The car just uses this sensor to also determine a rpm for the wheel and does some comparison with the other wheels ABS sensor and reaches a decision if one (or more?) wheels speed differs from the others due to smaller wheel diameter if at lower tire pressure. I'm sure it's not a real sensitive or accurate 'answer' it arrives at, but it is effective enough that after getting such an alarm and stopping and looking at the tires I can't always tell which is the lower one just by eye, I have to measure manual to be sure in most cases.

Lefty

mmcp42

there are only 10 types of people
them that understands binary
and them that doesn't

retrolefty


:cheesy grin:


Yea, take a bow. It's a neat example of thinking outside the box. They had an existing sensor(s) and the computing power to spare to come up with a new alarm function without having to add any new hardware.

I was impressed when I first researched it. I was curious because the first time I had to get new tires I inspected the wheels and brake assembly and couldn't see anything I could relate to a tire pressure sensor. A little googling showed that there are two methods. The long haul trucks use a system that does rely on pressure sensors, and is quite expensive option. But it makes sense for them because with 18+ wheels it's not much help to say hey one might be low! The second method was as I explained, just a little freebie sensor based on existing tech already in the car.

Lefty

liudr

Man I have been driving 2-hand cheap cars. I should have gone with one with ABS! Good challenge! I won't be doing this on my cheap Taurus though.  :0 ;)

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