HP 45 High Precision Timer

[Sadsilence]

(09-20-2015 09:48 PM)cruff Wrote:  Well strictly speaking, if you an afford to order the minimum batch size, many crystal manufacturers will custom manufacture some for you. :-) You can order a 7.8432 MHz crystal off DigiKey, run it through a divide by 10 and only be slightly fast.

Of course you are right. I checked such opportunities, too. In the end, they are either too expensive or too complex or needs too much power or a combination of all. If there is a real demand of 784 kHz crystals, there would be a lot of manufactures. A customs design in 100 pieces range is beyond any reasonable budget.

Anything else but a matching crystal requires additional electronic parts.

When using preprogrammable oscillators an output level adaption would be necessary. But it is like they try to tease HP-45 owners ;-). Free available chips with preprogrammable frequencies below 1 MHz are rare. The parts in right frequency range are either in wrong supply range, have housings, not manageable for private use or require > 10 mA.

Programmable devices, I include your base frequency divide idea in that category, requires even more parts. Counter/Shifters with a lot of pins for frequency dividing, a precise voltage reference for VCOs or even a microcontroller for PLL stuff or oscillators with a programming interface and, when one chip is not able to handle 3.6 - 4.5V, a voltage regulation circuit. Besides limited space inside HP-45 you have to develope a special PCB...

Another problem is extreme accuracy when it comes to time measurement. 0.1% or 1% tolerances of devices (resisitors etc.) are normally regarded as very good. For a everyday timer 0.01% is regarded as "ok".

Of course, I would be glad, if there is an easier solution or I missed a 784 kHz crystal source or I understand HP-45 curcuits wrong. Feedback is highly appreciated.

Best regards,

Werner