Hi Bill,

Sorry for replying so late. Quite a number of public holidays recently.

I do not fully understand the first paragraph, but I think I can roughly
know the main idea. Anyway, do you still remember a previous thread on the
piclist on "Tilt / Angle Sensor".

I have enquired on the list for the cheapest priority encoder or a
potentiometer(those with a shaft and ball bearing). The main idea is to
construct a Tilt sensor by attaching a weight to the shaft. One piclister
actually suggested using the mechanism inside a typical mouse to construct a
Tilt/Angle sensor as compare to using a typical priority encoder. One of the
reason for not using a priority encoder or a potentiometer(with ball
bearing) was that it is still expensive (of course,much less compare to
accelerometer) and they are not meant to take any sort of weight on the
shaft.

So back to submodule and main module. When the car is not stationary (
moving around), the main module will ignore whatever data that is send by
the tilt sensor submodule. Only when the car is armed, the main module will
constantly check for a signal from the submodule to show that the car is
jack up. There will be a 2 minute delay before the actual reading by the
main module to allow the tilt sensor to settle down. As for the internal of
the tilt sensor, the controller will assume that the car is stationary after
receiving no changes/minimal changes for a 1 min period. Any changes after
the 1 minute window period will result in the generation of a Low to the
main module by the controller to signify that the car is jacked up. Do you
foresee any problem with this?

In my opinion, the above implementation is kind of less complicated in the
aspect of the communication between the main module and the submodule since
it will be one way, but there will be more work to do at the Tilt sensor
module.

The other method was to send some signals to the submodule to inform that
the car is stationary and armed. All the submodule has to do is to check for
any changes above the level tolerated. In this way, the controller in the
tilt sensor module will not be bothered to constantly searching for the
'stationary level' as a reference. The communication between the modules
will be in the form of send -> acknowledge type.

Thanks.

Rgds,
pang


----- Original Message -----
From: "Bill & Pookie" <>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, December 06, 2002 12:19 AM
Subject: Re: [PIC]:Communication on a single line


> This is an interesting application.
>
> Seems like all the data you want will be real time
> data and there will not be any logged data.  So
> there is no chance of loosing any log messages.
> But maybe have a event reported for a long period
> of time incase the first message is not received.
> The event sets a two minute timer in the sub
> module and the sub module starts counting down the
> timer.  When the sub module reports, it reports
> the event as well the time remaining in the timer.
> This would stretch the event out and also indicate
> each new event to the same sub module by the state
> of the timer.
>
> You mention having the main module signal the sub
> module to disarm the stage.  This may not be
> necessary.  The main module can just ignore the
> alarms from the stages and still monitor them
> while you are in control of the car.  This would
> also notify you if one of the sub modules stopped
> working.
>
> You haven't mentioned how you plan to enter the
> car without the alarm going off, not how to exit
> car and turn on alarm.  One concept that might be
> useful is to have the main module arm itself after
> a preset amount of time where there is no activity
> in nor on the car.
>
> Bill
>
>

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