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HP 45 High Precision Timer
10-13-2015, 02:48 PM (This post was last modified: 10-21-2015 02:06 PM by Sadsilence.)
Post: #8
HP 45 Timer
Thanks for your feedback and thanks to all others spending HP 45 calculators and time to give curcuit a chance.

As far as I know every installation reported back was sucessful in the end (thanks to patience of some users) and no calculator passed away. I got several improvement hints, too.

Achieved accuracy is between +-100 ppm (1 s every 3 hours) and +-300 ppm (1s every hour). That is not bad and several hundred times better than normal 100000 ppm (10%) tolerance but misses aim of +-100 ppm by a small margin. Nevertheless, keep human reaction time for pressing start/stop button or mean time buttons in mind it is more than enough for an accurate measurement in some hours range. (Besides the fact, that is more funny than reasonable using an HP 45 as stopwatch ;-)).

On the other side any further accuracy improvement based on that technology is mere luck, due to limited temperature compensation of used oscillator chip and adjustment resistors as well as some voltage supply influcence and output signal jitter.

Anyway, at the moment there are no curcuits left (no more tiny PCBs).

With still a few inquiries and maybe some more interest I am currently testing an improved version (HP 45 Timer 2.0 ;-)), based on a preprogrammable MEMS oscillator with +- 20 ppm. Same PCB, same connection scheme to HP 45 (existing 1.0 version can be replaced without complete disassembly/desoldering wires from HP 45 mainboard) , no time consuming selection of adjustment resistors for me, better output signal and another 10 times accuracy improvement over whole temperature range and power supply range.

First 24h test showed a derivation of only -0.46s (-5,3 ppm). That is in range of human reaction time. So not a very precise measurement, but good enough to say derivation is less than 1s a day with moderate temperature variation and supply voltage variation.

- difficult to solder (no real user problem, as I test every unit before shipment anyway)
- 8 mA typical supply current which is 10 times higher compared to first version. HP 45 itself has 120 mA - 150 mA typical supply current. Overall consumption increases by 5-7%. In other words: When your brand new 2500 mAh replacement battery pack is good enough for 15h of wireless operation time you will loose about one hour.

Before building a second batch, several tests with a second prototype unit and a second HP 45 are necessary together with a revised guide. If for any reason V2.0 does not work, I will create some more V1.0 units. How many depends on your interest ;-).

Thanks for your time.


(10-11-2015 11:18 AM)Duane Hess Wrote:  Received mine today. Thank you very much!

Arrived safe & sound.
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Messages In This Thread
HP 45 High Precision Timer - Sadsilence - 09-20-2015, 06:44 PM
RE: HP 45 High Precision Timer - cruff - 09-20-2015, 09:48 PM
RE: HP 45 High Precision Timer - cruff - 09-21-2015, 05:58 PM
HP 45 Timer - Sadsilence - 10-13-2015 02:48 PM
RE: HP 45 High Precision Timer - TASP - 10-14-2015, 02:37 AM

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