Best place to buy a Dallas DS12887A?

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Best place to buy a Dallas DS12887A?

Postby Brume » Tue May 17, 2016 11:38 am

Hi all,

As everyone, I need to replace the DS1287A on my Falcon(s).
Many retailers are still selling them, but looks like some of them are defect or discharged.

Is there a trusted place where I order some DS1287A? I've seen them for less than 2 € on eBay, are they reliable?
Also is there a way to test the battery before soldering it on the mainboard? Or will it be the big suprise after the open-heart surgery?

Thanks in advance for your help.

Brume

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Re: Best place to buy a Dallas DS1287A?

Postby bugs » Tue May 17, 2016 12:11 pm

I have got them on ebay a few times, never a problem. If you put a low profile socket then you never have to worry about soldering again.
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Re: Best place to buy a Dallas DS1287A?

Postby Arne » Tue May 17, 2016 1:09 pm

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Re: Best place to buy a Dallas DS1287A?

Postby ctirad » Tue May 17, 2016 7:36 pm


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Re: Best place to buy a Dallas DS1287A?

Postby exxos » Tue May 17, 2016 8:02 pm



oh wow thats awesome. I didn't know there was a RTC without internal battery (never thought to look!)
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Re: Best place to buy a Dallas DS1287A?

Postby bartek030 » Tue May 17, 2016 9:52 pm

Brume wrote:Is there a trusted place where I order some DS1287A?


TME, genuine chips, 2015/2016 year of production.

http://www.tme.eu/en/details/ds12887+/r ... im-dallas/

If shipping is more than 5 euros, I can ship it to You, I have some in stock.

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Re: Best place to buy a Dallas DS12887A?

Postby alexh » Wed May 18, 2016 12:13 pm

The best place to get them is direct from Maxim-Dallas on their website. They will send pretty much anyone a test sample or two free of charge

https://www.maximintegrated.com/en/prod ... 2887A.html

You can still get the DS12887A+ which AFAIR works on the Falcon

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Re: Best place to buy a Dallas DS1287A?

Postby catmando » Wed May 18, 2016 4:06 pm

exxos wrote:


oh wow thats awesome. I didn't know there was a RTC without internal battery (never thought to look!)



Great, if someone has the means to make a batch I'd be interested, here's the PCB files

Maeslin_RTC_Falcon_NVRAM_Design.zip


and parts list/instructions

Code: Select all

DS12887 substitute with replaceable battery.

Uses:
- 1x DS12885/BQ3285 in SOIC package
- 1x 32.768kHz crystal, SMD, 6pF
- 1x CR1220 battery holder (Harwin S8411-45R or equivalent)
- 1x adapter socket (CNC Tech 220-1-24-006) with some pins cut/removed

‘Flat’ pins on the socket adapter go on the module underside, ‘tapered’ pins go to the motherboard.
Battery side of the PCB is ‘up’.
The inner brace of the socket adapter has to be carefully removed.


Orginal link here

Also added to wiki
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Re: Best place to buy a Dallas DS12887A?

Postby catmando » Wed May 18, 2016 4:14 pm

Can anyone see what's the difference between the original and v3 version?

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Re: Best place to buy a Dallas DS12887A?

Postby exxos » Wed May 18, 2016 4:33 pm

I can do a batch if theres interest. I need do get some smaller PCB's done soon anyway. I'd also be tempted to try a super capacitor instead of a battery. I might get one and see how long it takes to discharge :)
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Re: Best place to buy a Dallas DS12887A?

Postby catmando » Wed May 18, 2016 6:30 pm

exxos wrote:I can do a batch if theres interest. I need do get some smaller PCB's done soon anyway. I'd also be tempted to try a super capacitor instead of a battery. I might get one and see how long it takes to discharge :)


+1 for this (would the cap still fit without modifying the shielding?)
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Re: Best place to buy a Dallas DS1287A?

Postby catmando » Wed May 18, 2016 6:33 pm



Is Martin on this forum at all?
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Re: Best place to buy a Dallas DS12887A?

Postby ldv-01 » Wed May 18, 2016 7:40 pm

exxos wrote:I can do a batch if theres interest. I need do get some smaller PCB's done soon anyway. I'd also be tempted to try a super capacitor instead of a battery. I might get one and see how long it takes to discharge :)

Interested in 2 ..

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Re: Best place to buy a Dallas DS12887A?

Postby exxos » Wed May 18, 2016 8:23 pm

catmando wrote:
+1 for this (would the cap still fit without modifying the shielding?)


i'm looking at "coin" style caps, so likely they will be smaller than the battery. They are 1F or there abouts. Looking at the datasheet and the current drawn in "standby" it works out at about 20megohms resistance. So I will get a cap, and go from 20m.. 2m... 200k and see how long it takes to discharge to about 2volts or whatever the lower voltage limit is. Then if I times up by 100x I should be able to get a idea on how long the cap will last to power the IC over a battery. I would imagine the internal resistance of the capacitor being lower than 20M, so would imagine it should be good for a few months in between charges. Will order one and put it to the test before deciding on anything else.
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Re: Best place to buy a Dallas DS12887A?

Postby catmando » Wed May 18, 2016 9:06 pm

exxos wrote:
catmando wrote:
+1 for this (would the cap still fit without modifying the shielding?)


i'm looking at "coin" style caps, so likely they will be smaller than the battery. They are 1F or there abouts. Looking at the datasheet and the current drawn in "standby" it works out at about 20megohms resistance. So I will get a cap, and go from 20m.. 2m... 200k and see how long it takes to discharge to about 2volts or whatever the lower voltage limit is. Then if I times up by 100x I should be able to get a idea on how long the cap will last to power the IC over a battery. I would imagine the internal resistance of the capacitor being lower than 20M, so would imagine it should be good for a few months in between charges. Will order one and put it to the test before deciding on anything else.


Think I'd still prefer a battery, sometimes it can several months before I revisit my Falcon
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Re: Best place to buy a Dallas DS12887A?

Postby exxos » Wed May 18, 2016 9:52 pm

I ran a simulation based on 1F 20Mohms and from 5V to 2.5V takes 24weeks. The super cap would overhang the PCB a little as they are 20mm dia. I guess a larger capacitor would last a year or more. Though the cost isn't likely as cheap as a battery.

I will see if there are any rechargeable batteries.. that would be a possible idea..
EDIT
http://uk.farnell.com/varta/55608303059/battery-pcb-mount-3-6v/dp/279341
Would have to overhang the socket a fair bit to gain height.. My falcon's dont have the metalwork so not sure what the height is unless someone can measure and take a image for me..
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Re: Best place to buy a Dallas DS1287A?

Postby ctirad » Wed May 18, 2016 10:06 pm

catmando wrote:


Is Martin on this forum at all?


I doubt that, but you can write him a mail.

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Re: Best place to buy a Dallas DS12887A?

Postby catmando » Thu May 19, 2016 12:15 am

exxos wrote:I ran a simulation based on 1F 20Mohms and from 5V to 2.5V takes 24weeks. The super cap would overhang the PCB a little as they are 20mm dia. I guess a larger capacitor would last a year or more. Though the cost isn't likely as cheap as a battery.

I will see if there are any rechargeable batteries.. that would be a possible idea..
EDIT
http://uk.farnell.com/varta/55608303059/battery-pcb-mount-3-6v/dp/279341
Would have to overhang the socket a fair bit to gain height.. My falcon's dont have the metalwork so not sure what the height is unless someone can measure and take a image for me..


Arne's version has the overhang

Image

I can measure the distance on my machine unless someone beats me to it
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Re: Best place to buy a Dallas DS12887A?

Postby exxos » Thu May 19, 2016 10:35 am

Yeah it be a similar type of thing. Though using a rechargeable battery means it is taller, so has to be mounted further back to miss the metal shield. They are about 20mm high. So that plus 2mm for the PCB, and about 3mm for header pins, then needs about 25mm height between the motherboard and metalwork. If people are likely to fit it into a socket, then it will need more height clearance.

EDIT1: While the SMT RTC IC looked cool as it was a compact solution, As the battery is likely going to be moved a fair bit back, no real reason why the DIP 885 RTC couldn't be used like The image above. This would mean people could assemble the kit themselves a lot easier..
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Re: Best place to buy a Dallas DS12887A?

Postby exxos » Thu May 19, 2016 9:17 pm

Finally found a internal image. I can only find the top part of the metalwork, I fear I might have lost/chucked the front part, was like 20 years ago.. :roll:

Image

Looking at the keyboard pillar in relation the metalwork and top of the RAM card, likely a thick piece of card ontop of the RAM card is the maximum height there is, and pretty much the front of the RAM card is where the angle starts on the metal. So at least it gives me a idea to work with.

i've ordered the battery I have in mind and designed the PCB, but obviously need to do a mock board to see if it will all physically fit. I think it will..
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Re: Best place to buy a Dallas DS12887A?

Postby Greenious » Thu May 19, 2016 10:10 pm

Actually, you can do it the old Mega ST way, and just go with a simple 2AA battery pack connected to the chip, and ppl can put the batteries wherever they want/have room.

I suspect it will be cheaper and a lot less work.

Since some of these compatible RTC ICs got pins for external battery backup, it seems the easiest and cheapest way to go.
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Re: Best place to buy a Dallas DS12887A?

Postby Atari030 » Thu May 19, 2016 11:35 pm

You'd be right on the RAM card, Chris. Most under sling the SIMM as it is the only way to fit it in. I have a 30 pin card in my stock Falcon and the card extends behind the floppy. The speaker has to be removed to fit.

I like the coin cell idea, small, easily tucked away and a simple circuit. You could run a fly lead to the battery and mount it on the shielding somewhere.

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Re: Best place to buy a Dallas DS12887A?

Postby catmando » Fri May 20, 2016 7:24 am

exxos wrote:Yeah it be a similar type of thing. Though using a rechargeable battery means it is taller, so has to be mounted further back to miss the metal shield. They are about 20mm high. So that plus 2mm for the PCB, and about 3mm for header pins, then needs about 25mm height between the motherboard and metalwork. If people are likely to fit it into a socket, then it will need more height clearance.


Would people even need the socket since the battery can now be replaced? Socket was only needed for the original method of replacing the whole chip.
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Re: Best place to buy a Dallas DS12887A?

Postby catmando » Fri May 20, 2016 7:28 am

Here's another picture of Arne's version in place (you can see the ram card in relation to the post top right)

Image
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Re: Best place to buy a Dallas DS12887A?

Postby exxos » Fri May 20, 2016 7:41 am

catmando wrote:Would people even need the socket since the battery can now be replaced? Socket was only needed for the original method of replacing the whole chip.


Probably not, though everyone seems obsessed with fitting stuff in sockets :shrug: Best method would be to solder the PCB to the motherboard, and solder the IC to the RTC PCB. Then it all sits lower down.


catmando wrote:Here's another picture of Arne's version in place (you can see the ram card in relation to the post top right)



Yeah pretty much same idea, though the battery would be a little taller. So just have to check on that hopefully later.
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