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DS12887 drop-in replacement

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Reply 140 of 175, by i486_inside

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I've replaced a couple ds12887s with new clock chips and it got me thinking more about making permanent replacement chips. I'm almost thinking about buying a bulk quantity of cheap DS12885s in DIP-24 encapsulation from china and making a small cost effective production line of replacement ds12887s.

There's a couple things I'm still thinking about though, What would people prefer on battery option, would you prefer a small coin cell on top of the chip, a large cr2 or cr123a holder on top of the chip, or would rather have a pin header so that you can hook up an external 2x(A)AA holder or external lithium battery holder for the size of your choosing.

If you were to use 2xAA or AAA I would recommend using the energizer ultimate lithium or similar lithium iron sulfide batteries since they have a very long shelf life, I think the expiration dates are 20 years from date of manufacture now, which implies very low self discharge, they shouldn't ever leak, and their discharge characteristics make them more suitable for CMOS applications than alkalines because they keep a high voltage above 1.4v for almost all of their capacity where as alkalines have a significant amount of capacity below 1.25V and the minimum Vbat votlage per the DS12885 datasheet is 2.5V.

Still thinking about how to attach the oscillator, there are several way I could do it.
- Use a surface mount oscillator and cut off the bottom of pins 2 and 3 and leave just the wider part of the top of the pins to use a solder pads so that I can mount the oscillator on the side of the chip, I would cut the pins off so that the solder joints are not reheated when it is soldered to a board and so that the solder joints wouldn't be flexed while being inserted into a socket.
- Use a can oscillator and stand it up and glue it to the side of the battery holder for mechanical support then either cut the pins short and solder to the wider part at the top of the pin or I could bend the pins up and solder to them.
- For an external battery header design I could mount a can oscillator to the top of the chip I could either bend the oscillator leads around the side of the chip and use the wide part of the pin as a solder pad or I could bend the ds12885's pins up around the top and leave the oscillator leads straight.
- I could put the chip in a turned pin socket and stand the oscillator up in the larger opening at the top of the turned pins and solder the oscillator and pins 2 and 3 into the socket permanently, then I could wither glue the oscilator to the side of the battery holder or bend it down to glue it to the top of the ds12885.
- Similar to the previous but I could cut pins 2 and 3 short and then use an IC socket to hold the oscillator pins while I solder them to what's left of pins 2 and 3.
- I could bend pins 2 and 3 underneath the IC and mount the oscillator to the under side of the IC which would fit fine in most open frame sockets but wouldn't work in a closed frame socket.
- I could include a socket that isn't permanently attached to the IC and with a turned pin socket I could solder the oscillator to the larger diameter part of pins 2 and 3 and glue the oscillator into the open frame part of the socket, or with a double wipe socket I could bend the pins underneath the socket and solder the oscillator to them then glue the oscillator into the open frame hole for additional mechanical support.

I know this is long and I'm probably putting too much thought into this but right now I am not working and I have way too much time until I have held my learners permit long enough so that I can get a drivers license and go look for a job.

Reply 141 of 175, by i486_inside

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I think I thought of a clean solution on how to use a DIP-24 , you could make an alt12(c)(8)87 for dip24 , For my idea you would glue the alt12(c)(8)87 pcb on top of the ds12(c)(8)87 and bend pins 2,3,16, and 20 up and solder them to their respective pads on the alt12(c)(8)87 , pins 2 and 3 would be brought out to pads to mount an oscillator, pin 16 would go to the negative terminal of the battery holder and pin 20 would go to the positive terminal of the battery holder. I refer to it as the alsDS12(c)(8)87 because using DIP-24 opens up the possibility to use a DS1285 or DS12C885 which I can't find in SOIC-24 packages, I don't think they made a DS1285 in SOIC-24 and I have no idea whether the DS12C885 was ever offered in SOIC-24 but I can only find DIP-24 or SOP24 packaged chips online.
It would probably be possible to make this with a single sided board would that cut down the costs of the PCBs any?

Reply 143 of 175, by Maeslin

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i486_inside wrote:

I think I thought of a clean solution on how to use a DIP-24 , you could make an alt12(c)(8)87 for dip24 , For my idea you would glue the alt12(c)(8)87 pcb on top of the ds12(c)(8)87 and bend pins 2,3,16, and 20 up and solder them to their respective pads on the alt12(c)(8)87 , pins 2 and 3 would be brought out to pads to mount an oscillator, pin 16 would go to the negative terminal of the battery holder and pin 20 would go to the positive terminal of the battery holder. I refer to it as the alsDS12(c)(8)87 because using DIP-24 opens up the possibility to use a DS1285 or DS12C885 which I can't find in SOIC-24 packages, I don't think they made a DS1285 in SOIC-24 and I have no idea whether the DS12C885 was ever offered in SOIC-24 but I can only find DIP-24 or SOP24 packaged chips online.
It would probably be possible to make this with a single sided board would that cut down the costs of the PCBs any?

The DS1285 and DS12885 are functionally identical, with the only difference being that the 12885 has 64kB of RAM added. The 'SOP' package is likely to be SOIC since the DS12885 was only ever made in 4 packages afaik: DIP, SOIC, PLCC and TQFP. The two latter ones have pins on all 4 sides and are more challenging to solder with an iron.

ia2115 wrote:

where or when cant this be bought or? 😉 I need a solution to all my older equipment with these types of rtc and batteries.

I decided against selling what I had even if I have a whole pile of them because shipping ends up being more expensive from here than the sale value of the assembled module itself and it seemed ridiculous to ask ~$20 shipping for a $15 item. My work unfortunately also keeps me offshore and out of internet range for extended periods, which makes the logistics of taking orders and shipping things complicated at the best of times.

It's why I made everything public on OSHPark here. For a bit of DIY. For ~$4.20 you get 3 PCBs. Procuring the other components is an exercise left to the builder. 😉

Batch orders of 5-10 or more might be more doable, as shipping becomes much more economical in bulk. As it stands, I have a dozen tested and ready but I will be offshore until mid-September.

Reply 144 of 175, by keropi

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I recently built some of these Maeslin - they work awesome !
thanks for sharing!

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Reply 145 of 175, by Vaudane

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Honestly these look so much better than Frankensteining an old RTC chip, and it bothers me having a dead battery attached to any electronics, regardless of how hermetically sealed it thinks it is. Good job 😀

And thank you for uploading the gerbers. I think I'll give PCB train a shout and give this a shot.

Reply 146 of 175, by matze79

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where do you buy the RTC ? i only find them at high prices, or only from china.

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Reply 148 of 175, by Maeslin

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Vaudane wrote:

Honestly these look so much better than Frankensteining an old RTC chip, and it bothers me having a dead battery attached to any electronics, regardless of how hermetically sealed it thinks it is. Good job 😀

And thank you for uploading the gerbers. I think I'll give PCB train a shout and give this a shot.

As a note, one of the only potential issues I can see coming up with the newer, non-castellated model that can use 'square pin' headers is that those pins might be too fat for the original chip holder or, if soldered to the motherboard, too fat for the pad holes in the motherboard PCB.

matze79 wrote:

where do you buy the RTC ? i only find them at high prices, or only from china.

Same here. Initially went with half from Digikey, half from Aliexpress and stress-tested both to compare. I'll see if I can find my original purchase order and, if the vendor still exists, will post the link here.

keropi wrote:

I recently built some of these Maeslin - they work awesome !

Glad to hear you like them!

I've also been working on a custom 6x RS232 + I2C or 8x RS232 PC/104 adapter but figuring out a convenient way to configure all the IRQs and memory addresses without a forest of jumpers makes things tricky. Nevermind juggling 8 IRQs if all the ports use individual ones (the PCB is meant to be able to use anything from IRQ2/9 to IRQ15 for more flexibility).

Reply 149 of 175, by Eleanor1967

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I also just ordered a 3 of those PCBs, really excited, thanks for designing these! I still have two questions:

- There is this "2 oz copper, 0.8mm thickness" option on oshpark, I didn't check that, should I have done this?
- I'm not sure which crystal I should use, could somebody be so kind and point me to one? (Are these what I need?)

Tanks again!

Reply 150 of 175, by BloodyCactus

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Maeslin wrote:

As a note, one of the only potential issues I can see coming up with the newer, non-castellated model that can use 'square pin' headers is that those pins might be too fat for the original chip holder or, if soldered to the motherboard, too fat for the pad holes in the motherboard PCB.

look up machine pin headers (round). can get different kinds. eg: these are not the fat square pins that dont fit in all pth.

machined%20pin-500x500.jpg

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Reply 151 of 175, by Vaudane

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I've ordered some PCBs from China. Sadly as I'm UK based, I can't get the shiny purple-ness of OSH Park without silly import costs. On the flipside, minimum order was 5 ($2 for 5 boards. $6 for import 🤣) if there's anyone else in the UK/EU that wants one of these, I'll make sure to order the other parts in bulk, build them all, and stick em on Ebay.

Edit: There are 2 SOICs available to me, the DS12885S+-ND and the DS12885SN+-ND. Does it matter what one is used?

Edit 2: It appears the only difference between the 2 is the operating temperature range!

Reply 152 of 175, by Maeslin

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BloodyCactus wrote:

look up machine pin headers (round). can get different kinds. eg: these are not the fat square pins that dont fit in all pth.

Yeah those are pretty much what the castellated version is meant for. It uses those headers 'stub side up' and the castellations are made wider to fit right around the wider cylindrical part of the pins. Of course, the non-castellated version will work just as well with those. 😁

Reply 153 of 175, by Maeslin

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Eleanor1967 wrote:
I also just ordered a 3 of those PCBs, really excited, thanks for designing these! I still have two questions: […]
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I also just ordered a 3 of those PCBs, really excited, thanks for designing these! I still have two questions:

- There is this "2 oz copper, 0.8mm thickness" option on oshpark, I didn't check that, should I have done this?
- I'm not sure which crystal I should use, could somebody be so kind and point me to one? (Are these what I need?)

Tanks again!

the 2oz copper is not necessary, that's for higher current applications.

Those aren't the right crystals; they would work in theory, but the contact spacing is likely wrong for the PCB. What you would be looking for are the common cylindrical kind, only with 'bent' pins;
CMR200T%20series,CMR250T%20series.jpg

It's pretty easy to get the 'straight pin' ones and bend them yourself too.

Reply 154 of 175, by TheFifthRace

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I have an OEC12B887A and I was wondering if this would work as a replacement for that. I can’t find a datasheet on the OEC so I don’t know how interchangeable they are with a Dallas RTC.

Edit:
To answer my own question, I desoldered the OEC12B887A from my motherboard and on the silk screen it showed a DS12887A. I put in a socket and popped in a DS12887A+ and it seems to work. So guess they're pretty much the same thing.

Reply 155 of 175, by olebakk

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I just wanted to send out a big thank you to Maeslin for this design. I got my PCB from PCBway and the other stuff from ebay - and put it together in half an hour or so. Works perfectly on the first of two motherboards I wanted to fix!

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Reply 156 of 175, by Maeslin

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olebakk wrote:

Works perfectly on the first of two motherboards I wanted to fix!

Glad to hear it works well for you! Sorry for the delay, for some reason there had been no notification of a new reply.

If you haven't done so, I recommend securing the 32khz crystal case to the PCB with 1-2 drops of superglue. Makes it less likely to just yank the solder pads off if the crystal ever gets snagged by something.

Reply 157 of 175, by feipoa

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I'm particularly fond of how the RTC's PCB colour matches the motherboard. Looks very natural.

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Reply 158 of 175, by Shadow Lord

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Hello All,

I have purchased a few of these from Maeslin and they are great! However, I now have a system that uses a DS1497 (basically a DS1495 w/ built in battery). Does anyone know if these would work as a replacement for the DS1497? TIA!