Neville and Jim and all, there are good pictures of tuning fork crystals at
http://en.wikipedia.org/wiki/Crystal_oscillator I think it is the 8x3 mm in size, which is available from China (10 units for 2.5$ including worldwide shipping). Assuming as a reference the diameter of the baseplate, say 2,5 mm without the can, the tines appear to be long in the order of 5 mm. It looks suitable for trimming (see, just below the tuning fork crystal, the picture of a trimmed round crystal). Trimming that way is common practice in crystal manufacturing, and this is what happens when you order a custom crystal (they have blanks which cover ranges). So I'm confident that the Q will not be affected so much. I think it is worth the try. Anyway, Neville, as a backup solution, I would be pleased to consider your design, and I think that others might have an interest too. I would recall that I actually know what sidereal time it is now, by a computer program, but my problem is that I have to rotare a mini torsion balance by means of a low power drawing setup. Cheers, Antonio I8IOV >Hi Antonio, >the 32kHz Xtals are 2mm long tuning forks (that is what I believe >although I have not opened one). >You would have very little chance of modifying it and still have >enough Q left for it to oscillate. >As an alternative you could build an external circuit (a few uA at 3V >supply) and generate a signal to inject into >the existing Xtal osc with the Xtal removed. >The type of circuit that I would build would be a cmos binary divider >connected to a quad gate. >The 4 gate inputs connect to selected binary stages of the divider. >When the gate decodes the >selected number, an extra pulse is added to the count chain. The >output is thus shifted to a higher >frequency. >If you are interested I can try to design the circuit for you, I have >intend to build a Siderial clock >dial for my TBolt. >cheers, Neville Michie > >On 17/05/2011, at 7:58 AM, iov...@inwind.it wrote: > >> Neville, >> at present I have not enough skill with micros to solve the problem. >> I think I will try modifying a crystal. This would not be that >> difficult using >> a lapping sheet or the like. And opening the can would be quite >> easy using hot >> air. This is the fastest way for me, and the device will continue >> to be powered >> by a simple AA cell, which is a non negligible advantage in my >> application. >> All the best, >> Antonio I8IOV >> >>> Antonio, >>> it is quite easy to make an external circuit that uses a 32kHz xtal >>> and divides >>> it down to siderial seconds. It is also easy to drive most analog >>> quartz clock movements from >>> an external circuit. >>> Just what signal do you need? What frequency? and what does it drive? >>> (an alternate polarity >>> quartz clock motor?) >>> It can also be done with a micro if you have the skills. >>> cheers, Neville Michie _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.