On a scale of 1 to 10, how silly is this?

[jcarmody]

I want to make a very rough guess at the resistance of a switch as it closes, and I'm using a USB-6009 to do it.  A technician was testing these (pressure) switches by monitoring the resistance while slowly increasing the pressure and I was able to identify the ones he identified as "bad" using this method.  Will I lose my Engineer card for this?  I had half a mind to post this to the Rube Goldberg thread, but that's the half I'm using to do this quality work.

I did say "very rough guess"...  But!  It does give very useful results!

Good switch (very clean transition from open to closed):

Bad switch (notice the noisy line where the "good" switch was vertical):

Bouncy switch (this one is a very bad switch):

Bad witch:

[crossrulz]

So it looks like you are using P0.0 as a power supply?  Not sure I like that since you are current limiting the digital output.  It would be better if you put a resistor in series with P0.0 (AI1 still tied directly to S1).  You could also use the +5V output of the USB-6009 instead of the digital line.

[jcarmody]

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@crossrulz wrote:

So it looks like you are using P0.0 as a power supply? 

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No.  I'm using that as a digital input to know when the switch closes/opens (so I can record the pressure transducer connected to AI0).  Let me think about your suggestion. Half a mind...

[crossrulz]

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@jcarmody wrote:

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@crossrulz wrote:

So it looks like you are using P0.0 as a power supply? 

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No.  I'm using that as a digital input to know when the switch closes/opens (so I can record the pressure transducer connected to AI0).

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Ok, that makes a lot more sense.  And then you just depend on the built-in pull up resistor on the digital input (4.7kOhm to +5V, yep you're good).

[altenbach]

Now all you needs it to apply some smart processing and automatically reduce the entire measurement to a simple boolean output: GOOD or BAD. 

[Ben]

It was not silly until I saw bad (s)witch. Very nice touch by the way.

On a related thought...

My eldest G-daughter loved that movie when she was way young (she is a whole eight years old now). We were sitting down for another viewing when I quizzed her...

Grampa: "Olivia, which of the characters do we see first?" (expecting her to say the Scarecrow.)

Olivia: "The lion".

And to Grampa's surprise, she was right! As the movie opened the MGM Lion roared and taught me she was smarter than I thought!

Ben

[AnalogKid2DigitalMan]

Jim:

11? 🙂 Not so silly if it works reliably.

Ben:

And on the Lion's 3rd roar that is when you start playing 'The Dark Side of the Moon'! It is uncanny.

-AK2DM