very low pressure

TWO 32 KHZ watch crystals, one still in the can, one can removed, and beat them against each other. Wrap the master one in foam so it doesn't lock onto sympathetic vibrations from the slave. Its a common trick to use 32 khz crystals in atomic force microscopes, and they will see the pressure change. Much better then my AL can idea. You might put a vane on one leg of the open xtal.

The master xtal can is still under vacuum and is the reference.

I've made lots of sensors this way, including for a AFM at my previous employer.

Steve Roberts.

I assume that you were running the AFM as a crystal oscillator and looking at the phase to get the force gradient? The other approach is external excitation, but that could be pretty slow with a watch crystal.

Cheers,

Phil Hobbs

Normally at this point I would ask you why you are making your sensor in the shape of a toy, what you are planning on doing with the information, etc., but clearly you do not want to reveal what you are trying to accomplish (which is of course fine -- it is your choice). I strongly suspect that if you did tell us what you are trying to accomplish, someone here would come up with a cheaper, more reliable and simpler solution than the measure-air-pressure method that you have already decided on (that's what engineers do), but we will never know. Best of luck with your project.

Hey that's pretty clever. I assume the uncovered one will change as a result of ambient pressure? Will the exposed one corrode? I dont know what metal they are plated with is why I ask. Also does the effect work at or around 1 atmosphere? Do you remember what the resulting beat frequency is when exposed to the room temp and pressure? And any idea of the pressure/frequency relationship? Tony

I am making an effort to reply to all who have offered suggestions. It seems the decent thing to do. But it leaves me with little time to consider every response. You are perfectly correct. I made an error in syntax. Thank you for the lesson. Tony

Hello I am not trying to be coy. It is simply not my place to share the information without permission. And I have not sought that. Who the end user of the device is seems of little relevance. I appreciate your frustration and I apologize. Tony

Like I said, that's fine. The toy business is full of secrets. One time we caught an industrial spy who had managed to get inside our engineering department. He had made a fake badge (which, of course, would not open the electronic locks) and waited outside the door with a folder under each arm and a large coffee in each hand... No point in prosecuting; that would just result in a certain other toy company prosecuting...let's just say "prosecuting someone who may or may not be *our* spy." Industrial spies are alway hired by corporate lawyers who make sure that they maintain plausible deniability.