Stupid question number...WS34P



#18

Hello,

just recieved my parts for the timing and IR upgrades for the 30b.

And now for the stupid botanist (me) question.

Is the quartz crystal polarity dependent? Both leads are the same length and the crystal has no polarity marks. Assuming not polarity dependent to work.

I am using Katie Wassermans design with the trimming capacitor to allow the crystal current to be modified for accuracy. I will be creating a hole in the back of the case under the battery access cover to mount the cap and allow for easy access to the cap slot for adjusting the timer:

Trimming capacitor by Katie Wasserman

IR of course being added! I will be documenting this and adding it as an appendix to the book.

Cheers, Geoff


#19

The 41 time module implemented a clock correction factor perhaps the WP34 firmware could have this added.


#20

Yes the correction factor is excellent but does take alot of code. The Synchronar watch from the EARLY 70's also had an accuracy factor instead of the trimming cap.

At the moment, to save code and space, I think the cap is the way to go. It can be done quite elegantly depending on the amount of time you want to put into the project.

As far as the quartz crytsal polarity goes, answered that by installing the crystal and it functions in the calculator correctly.

Additionally if anyone out there needs very thin wire, I have used left over telephone cable. It comes with four wires colour coded and you simply peel them out of the surrounding cables. Nice source of thin insulated wires.

Cheers, Geoff

#21

Quote:
The 41 time module implemented a clock correction factor perhaps the WP34 firmware could have this added.

The lack of persistent memory is the problem here. If not, I would have implemented it already to calibrate Stopwatch on WP34s without a crystal.

The other solution would be to edit the firmware binary before flashing it. I'm not sure there is a real need anyway.


#22

Hi Geoff,

Just to point it out, quartz crystals are not polarized components. You can connect them in either position quite like a resistor or ceramic capacitor; (in case you may think that you have just been lucky in your 50% attempt with the 34... :-))

Cheers.

Diego.

PS, Just noticed Katie has replied faster while I was typing... ;-)

Edited: 15 June 2012, 3:43 p.m.

#23

Quote:
The other solution would be to edit the firmware binary before flashing it.

How would I go about changing this value in the binary? I know how to edit files. Any pointers to were this location can be found?

Thanks,

CJ


#24

[quote]
How would I go about changing this value in the binary? I know how to edit files. Any pointers to were this location can be found?
[/quote

You can't. Firmware does not support this. It could but as I said, this is not planned.

#25

It isn't so much adding support for a correction factor as where to store this in our already busting at the seams non-volatile RAM.

We've current got a bit or two of this RAM available and it has been down to zero bits free a couple of times. Storing a correction factor will require more than this to be rudimentary and a lot more to be properly useful.


- Pauli

#26

Crystals have no polarity, nor does the ceramic cap nor the trimmer cap.

You really need to mount this trimmer directly on the PCB if you use wire leads the wires themselves will be a very significance capacitance (a couple of pf) and just a slight movement of them will vary the oscillating frequency a lot. I think that you'll be able to mount the trimmer with the screw up and drill a hole in the back of the case for a small screwdriver.


#27

Thanks Diego and Katie,

didn't think about the wires changing the capacitance so it will be placedc on to the board.

Cheers, Geoff

#28

Looking Alexanders handout on his IR and Quartz additions (very helpful) I do have a problem interpreting one of the instructions.

It is stated that the IR printer anode should have the resistor installed in series and that this should be soldered to the R18. R18 has two solder points with a box around it. Alexanders wire in his photo (figure 8) appears to be soldered to the R18 solder point closer to the JTAG connector but also appears to have solder on the other R18 solder point adjacent.

My questions are/is which R18 point should have the anode soldered to it: the point closer to the JTAG or further away? Are both these points connected (jumped) by the solder application?

Geoff

Edited: 15 June 2012, 4:22 p.m.


#29

It doesn't matter where the resistor goes so long as it is there. It can even solder to the cathode.


- Pauli


#30

Thanks Pauli,

actually I was concerned with which attachments points to attach the wires at positions R18 and C29 on the board.

I take it this is correct:

cheers, Geoff


#31

Oops, misread the question. The connections in the photograph are correct.

The other pad of R18 connects to the base of Q2 (also unpopulated) so checking which is which is easy and shorting the two pads is also fine.

The C29 connection is for ground. The other side of this pad connects to the unpopulated U3 (pin 6), so again they can be shorted if you get it wrong.


- Pauli


#32

thanks Pauli

#33

Pauli,
I'll put that in my write up. That's ok with you?


#34

No objections at all.


- Pauli


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