very low pressure

twenty cents is pretty remarkable. So is being able to talk to an engineer that has done such a thing. I need to quantify the strength exhibited by squeezing a synthetic toy. A bytes worth of resolution would be great but 7 bits would be useful.

No, That is similar to what I used to derive the specs though.

Thank you, This is an excellent idea. I will investigate it now.

I like this idea a lot and have considerd it at length. I think however that the initial resistance would vary a lot from device to device. So I would have to use a programmable gain and adjustable offset to bring the signal to the adc. Like with the pressure sensors. I have not found a source of small quantity for experimenting with either.

That's how they do it in Trackpoint keyboards--iirc back in the day they ran the two ends of the resistive element from DACs to take care of rough gain and offset, and then used some software magic to get rid of the fine offset--they just wait for a long string of unchanging values, assume that means you aren't touching the pointing stick, and use that for the zero.

Alternatively you could use an unstrained patch of the same ink run as a half-bridge--e.g. put the ink down on some film, glue half of the film to the cylinder and let the other half just sit there. That would fix the rough offset, and the aforementioned software magic would take care of the rest.

Cheers,

Phil Hobbs

BTW carbon ink works fine with carbon-loaded Zebra connectors. That's what I did with the Footprints sensor,

Cheers,

Phil Hobbs

Hello Phil I read the article. That was a pretty awesome solution using red diodes. I thought hard about using some sort of capacitive lining or cylinder. But there are to many drawbacks. The idea of using an electret mike is great but for the decay rate because of the internal jfet. If I could extend the response to a second or .1hz that would probably work. That is what I am studying now anyway. Your article was a nice diversion. Tony

Some 20+ years ago there was a precursor to touchpads (so common on laptops now) called a force sensing resistor. Some thoughtful mechanical engineering with a sealed bulb should get you a useful signal.

BTW you want any sensor you use to have 2 to 5 x overrange without damage.

You apparently want this to be battery powered and for infrequent / irregular use, select your battery and operating rules accordingly, for some scenarios high output (and limited life once started) zinc-air batteries may be the best choice. Depends a lot on how you get the data form the "toy".

n,8,1 serial via ir led. Li-ion with the apropriate charge management. I have never heard of the "force sensing resistor". At least I dont remember. I will look it up. I was excited by the idea of using a mic for the sensor because it was pretty tough. I was concerned with the over pressure problems. And the cost of a low pressure sensor was to high. But I am having trouble thinking how to get a signal that will not decay before the signal itself is released. I could plot the decay rate but still not be able to tell it from an actual change in signal. Wow, Got a lot of hits on that so going to go read. Thanks Tony

That's interesting information, but it's not the information I asked for. You are telling me more details about you wanting to measure amount-of-squeezing information, but you haven't told me what you are planning to do with the amount-of-squeezing information. The essence of low-cost toy design is looking at the desired end result and devising a low-cost way of achieving that goal.

Here is an example that might help you to see what I am getting at:

Someone sold a concept to Mattel for a talking picture book -- run a wand over a picture and it talks about that picture. They gave it to me as a prototype and told me how to do it -- with magnetic ink under the pictures. There was an additional requirement that the wand had to read information from the plastic case that held the pictures, so they specified stick-on labels, again with magnetic ink. This meant that they had to specify flat spots for the labels (no compound curves), and that in turn meant extra plastic in order to meet strength requirements.

As the project manager/lead engineer, I treated the "here is how to do it" information as a suggestion. The *goal* was to wave the wand over a surface and output a sound. The inventor was focusing in on reading magnetic ink as the Only Way To Do It, just as you are focusing on measuring pressure. I was looking for a solution that could be silk-screened onto the pictures and the case without stick-on labels or restrictions on curved surfaces. First I looked into hiding a barcode-like pattern in the picture and using an optical wand, but that didn't work out, so I used a transparent/invisible ink that uses fluorescence to convert the red light from an LED to IR light that I could detect cheaply. This lowered the total cost by several cents, which is a big deal when a toy is being produced at a rate of

100,000 units per hour. The inventor didn't know that such inks exist, and I would imagine that you weren't aware of them either; most people are only aware of UV to visible fluorescence, not visible to IR fluorescence.

The *goal* of your project, should you choose to reveal it, won't be something like "measure very low pressure" or even "measure amount-of-squeezing" but will instead be something like "a teddy bear that verbally challenges a group of two- year-olds to a game where whoever hugs the hardest wins" (or whatever your actual goal is). If you are uncomfortable with revealing what you are trying to do on a newsgroup, my email address is on my website. I have no problem with signing an NDA; I am not in the business of stealing people's toy ideas. My business is turning them into mass-produced reality.

--
Guy Macon

Ok I understand where you are coming from. And I appreciate the offer. But the information is the goal. How much it is squeezed. And for how long. There is no interaction. I read Laser Focus World often. I enjoyed your story. Tony

So it's not a toy? It's a sensor?

--
Guy Macon

I have a story in Laser Focus World? What's the story about?

--
Guy Macon

How about gluing a piezo disk transducer from a buzzer to a aluminum cavity using Hysol C4 white epoxy, which is actually a vacuum grade epoxy, and watch the edges of the piezo signal?

Steve

Greetings all,

I've used "force sensing resistors" for similar apps. Suggest you google "force sensing Resistor" and/or FSR. If memory serves, Interlink and Tekscan are two manufacturers. I believe both these vendors use conductive inks. Resistance varies approx 1/Force; nice big signals. A single op-amp ckt can linearize these. May not be needed, esp. if your app is cost sensitive.

There's also a different type that uses tunneling, for these google Peratech QTC. I haven't used these, just read about them. (Highly nonlinear, but response over a wide range of forces.)

HTH,

Larry Pfeffer

How about one of these:

and a pot?

Have Fun! Rich

Interesting idea. I assume you mean watching how the point of resonance changes. Only aluminum is not exactly squeezable. Tony

I guess I was not clear. You implied I would not have been aware of flouresence other than the black light on a t-shirt variety. I pointed out that I read LFW regularly so you may have been mistaken.

It is a sensor with the shape of a toy. So it is both. A rubber squishy toy. That also happens to take note of how hard it is squeezed. I am afraid I don't know how to make it any clearer.