Programming a PIC is no problem. PM me if you are stuck. The PIC in question is still in production, widely available, and costs a couple of quid. What's novel in the article though is the "el cheapo" method of measuring gravity.
It seems that gravity variation really is measurable for near-surface voids, i.e. variations exceeding the noise level of the instrument. The eventual practical problem is that after finding a big void 10m below the surface ? are you then going to engineer a 10m deep shaft to get into it?
The circuit presented is a kind of resistance meter. On the face of it, a near 1% change in gravity, as shown on the LCD display in the article, would imply a void of perhaps 1/100th of a planet in proportion? I?m sure Dave Gibson can put me right on the maths, and provide an interesting paper in the next BCRA CREG journal about gravity and caves. Indeed, a cave which is 1% of the planet in volume would be ?very interesting? to visit.
Using the microcontroller?s hardware clock as a yardstick rather than some internal or external A/D module is a much more accurate way to measure things, which is a hopeful feature of this design. The PIC chosen could only resolve voltage to 1 in 1024 parts using its internal A/D unit. As this chip?s max clock rate is 2MHz, this implies that ?the thing measured? can be resolved to half a microsecond at best, so call that 1 in a million parts, which is about 1000 times better than if its A/D unit had been used for that purpose.
An exceedingly stable power supply is also of the essence for measuring voltages to incredibly fine resolution, and that?s definitely not going to be optimal with just a 7805 and just a 100nF capacitor across its output, as shown in the circuit.
But the ideas are interesting in principle and it?s a use for all those bits of anti-static foam occuping my desk drawers rather than opt for some sort of strain-guage as used in digital bathroom scales.
Anyone taken bathroom scales to bits to find out how they really work? They're incredibly cheap. I have this vision of a caver walking across an upland landscape, with bathroom scales in hand, weighing themself evey few steps to determine if there is an unknown void below...