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02-22-2016, 09:40 AM   #1
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K-Mount digital pin protocol, power supply

Hi,
I have non-working Tokina AT-X PRO AF 28-70mm 1:2.6-2.8 lens. Problem is broken flexible flat cable leading from internal chip to the K-mount pins. As I am not able to solder it back together I am searching for alternative repair solution. As can be seen from Bojidar's pages (Features and Operation of the Ka Mount) most of the pins are hardcoded and easy to repair. There is only one digital-info contact. So it should be easy to repair 5 wire flexible cable with only one wire and hard-code other KA mount pins.

If there is only 1 wire serial protocol, does it also include power supply? Or the power is transmitted over other pins? Why are there so many wires if most of the pins can be hardcoded by just connecting/disconnecting from the ground?

Thanks in advance,
Martin

02-22-2016, 10:27 AM   #2
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QuoteOriginally posted by mjedlick Quote
If there is only 1 wire serial protocol, does it also include power supply? Or the power is transmitted over other pins? Why are there so many wires if most of the pins can be hardcoded by just connecting/disconnecting from the ground?
they are all wired to "speak" to the body : aperture ain't constant so the lens need to change the connectivity of each pin to tell the body.
02-22-2016, 10:52 AM   #3
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All pins are common though the mount face and none but the data pin are used for serial communication. It is possible for power to be supplied through the auto-zoom contacts as well, but is not required for compliance with the KAF protocol.

Bjoridar Dimitrov's K-mount page may be helpful.

Summary of the K-Mount Evolution, Names, and Features

K-Mount Evolution, Features and Operation

The second linked page is sort of strange in that the sub-topics are not prominently called out as navigation. The two lists at the page bottom provide links to detail pages for each historic Pentax variant of the mount.


Steve
02-22-2016, 10:58 AM   #4
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QuoteOriginally posted by aurele Quote
aperture ain't constant so the lens need to change the connectivity of each pin to tell the body
That is where things may get complicated. Lenses may do this by dynamically switching the contact state using a small printed circuit board. I am not sure, but have been of the understanding that the data pin may offer override information through that interface essentially negating the other pins. I suppose I could do an experiment using tape to insulate all but the data pin and "A" pin to test that hypothesis.


Steve

02-22-2016, 12:57 PM   #5
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QuoteOriginally posted by stevebrot Quote
That is where things may get complicated. Lenses may do this by dynamically switching the contact state using a small printed circuit board. I am not sure, but have been of the understanding that the data pin may offer override information through that interface essentially negating the other pins. I suppose I could do an experiment using tape to insulate all but the data pin and "A" pin to test that hypothesis.
i've a "deconsctructed" Sigma 28-70 f28-4, and there is indeed a small chip connected to the pins trough a wire. After some testing it appeared that the Data pin translate the focal lenght as you zoom, but also some other data like the estimated size of the lens (to tell if there will be some problme with the flash and lens size), and other that i don't understand but mainly what you cna find in the exif of a photo.
If you keep the data pin connected but not the rest, there is some disfonction or some error in the program P or AV.
02-22-2016, 02:44 PM   #6
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QuoteOriginally posted by aurele Quote
aperture ain't constant so the lens need to change the connectivity of each pin to tell the body
As I understand Bojidar Dimitrov's description it provides maximum/minimum values for aperture, so it should not be such a problem in my case for min values between 1:2.6-2.8 in the zoom interval.

QuoteOriginally posted by stevebrot Quote
It is possible for power to be supplied through the auto-zoom contacts as well, but is not required for compliance with the KAF protocol.
To be sure: only one pin is enough for data and power in this case? So I will just have to guess how to get ground to the lens chip. All wires are connected to the pins and none directly to the mount body (ground), but there must be ground wire connected somehow. Do you have some tips?

"A" pin is mechanically coupled to the aperture, so this is not a problem.

Thank you guys for your answers.
02-23-2016, 03:53 AM   #7
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QuoteOriginally posted by mjedlick Quote
To be sure: only one pin is enough for data and power in this case? So I will just have to guess how to get ground to the lens chip. All wires are connected to the pins and none directly to the mount body (ground), but there must be ground wire connected somehow. Do you have some tips?

"A" pin is mechanically coupled to the aperture, so this is not a problem.

Thank you guys for your answers.
you need two pin to create an electrical circuit, otherwise it won't work. Depending on the lens, some use the metal mount to do it, some use the power coming trought the other pin.


The aperture in the K/M lens is linear (meaning for every EV step, the lever move the same distance), the aperture in A/F/FA/DFA is exponential (meaning that for every EV step, the lever move a different distance).
If you use the data pin without the other pin, the lens / body don't understand something : the exposure will be off except wide open. At least that's what happened with my sigma lens.
02-24-2016, 08:03 AM   #8
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QuoteOriginally posted by aurele Quote

The aperture in the K/M lens is linear (meaning for every EV step, the lever move the same distance), the aperture in A/F/FA/DFA is exponential (meaning that for every EV step, the lever move a different distance).
If you use the data pin without the other pin, the lens / body don't understand something : the exposure will be off except wide open. At least that's what happened with my sigma lens.
Wasn't it the opposite?

02-24-2016, 09:32 AM   #9
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QuoteOriginally posted by aurele Quote
you need two pin to create an electrical circuit, otherwise it won't work. Depending on the lens, some use the metal mount to do it, some use the power coming trought the other pin.


The aperture in the K/M lens is linear (meaning for every EV step, the lever move the same distance), the aperture in A/F/FA/DFA is exponential (meaning that for every EV step, the lever move a different distance).
If you use the data pin without the other pin, the lens / body don't understand something : the exposure will be off except wide open. At least that's what happened with my sigma lens.
Hi,

I have a Vivitar 28mm with "A" on the aperture ring. Would what you said (either the non-linearity or the data pin contact) explain why when I use it with my K-x and K-r, it seems to underexpose? Which would it be (i.e., do I have to add contact to the mount side of the Vivitar?)?

Thanks,
Jim
02-24-2016, 01:43 PM   #10
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QuoteOriginally posted by ohaya Quote
have a Vivitar 28mm with "A" on the aperture ring. Would what you said (either the non-linearity or the data pin contact) explain why when I use it with my K-x and K-r it seems to underexpose? Which would it be (i.e., do I have to add contact to the mount side of the Vivitar?)?
No...


Steve

Last edited by stevebrot; 06-26-2016 at 02:41 PM.
06-26-2016, 01:09 PM   #11
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It could well use something like 1-wire from Dallas Semiconductor:

https://en.wikipedia.org/wiki/1-Wire

---------- Post added 06-26-16 at 01:51 PM ----------

For example, look at the DS28E04:

https://www.maximintegrated.com/en/products/digital/memory-products/DS28E04-100.html
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