DS1742 NVRAM Chip Replacement

cz7asm

New member
Dec 9, 2020
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3
Hi,

I was constantly having problems with Fuels and DS1742 chips (L1 NVRAM & timekeeping). They became difficult to buy and I often received faulty pieces. The issue is that Fuel doesnt start if the chip is faulty or missing. Long story short, I finally found some time to build a compatible circuit that uses a replaceable battery.
So far it seems to be working, still need a few days to test it properly.

If you can think of any test cases or something else I could try, let me know.

If anyone is interested in getting oneI think I will be able to sell these for around 65 USD. The price of parts doubled over the last year so hopefully this trend will not continue. I think I can manage shiping for under 15 USD to US, a bit less to EU.

Hopefully it will prove reliable!

09E1ADAD-E2F4-42A9-96B5-9FE7D335E7DF.jpegF9D19701-C216-47B7-B8E4-0B106CF1E010.jpeg
 
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Elf

Storybook
Feb 4, 2019
702
195
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Western United States
Great work, it's nice to see more RTC replacements! :)
One of the register-compatible surface mount parallel RTC chips I'd guess? It's tough, a lot of the line seems to be going to I2C now.
 

cz7asm

New member
Dec 9, 2020
19
15
3
Great work, it's nice to see more RTC replacements! :)
One of the register-compatible surface mount parallel RTC chips I'd guess? It's tough, a lot of the line seems to be going to I2C now.
Yes, it's based on Dallas 155x series.

I did a current consumption test - 1.3uA during standby. The battery wasn't new, I measured 3.0V so I assume that the current would be a tiny bit less with a newer battery. I think this should give a pretty long run even with an ordinary CR2032 battery.

IMG-3736.jpg

I already got some feedback that the price is quite high. This might be true, but it's given by the price of components, PCB and work. At the time I was getting the components there wasn't one EU source that would have the Dallas IC's so I ordered from US, which accumulated additional customs and tax fees. So now an IC that would normally cost 13 USD cost me 20 (I'm looking at you DigiKey for splitting my order into 3 shipments and FedEx charging 20 USD for each as a customs checkout fee!) At the end if my expense is ~40 USD then selling the board for 60 isn't a crime...I hope. I'm sure someone could produce it much cheaper but that wasn't my primary goal.
 
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Elf

Storybook
Feb 4, 2019
702
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Western United States
I definitely understand the reason behind the price being high!

Many people will balk at that price I am sure, but peoples' price expectations are set by mass manufactured goods, for better or worse. As an example, for an ATX power supply that produces 600 watts that one could buy for $50 on amazon, if you were to make it yourself in small volume counting the BOM cost from DigiKey, the iteration on the designs and PCBs, etc. one could easily sink thousands of dollars into it just to produce one unit. The next unit might still cost you a few hundred dollars to produce.

What doesn't get considered when purchasing consumer goods -- where the price expectations are set -- is that the iterative design costs are spread over hundreds of thousands of units or more, that the components and every piece of the BOM sourced at those volumes (and not necessarily from premium outlets like Digikey) are a small fraction of the cost they are to the hobbyist, etc.

Unfortunately small volume electronics and high price just go hand in hand, unless one eventually does something like increasing the quantities a bit and outsourcing the assembly process.

Thanks for making these though, at some point I may need one :)
 
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cz7asm

New member
Dec 9, 2020
19
15
3
Just a quick update. So far the module has been successfully tested with these SGI machines:
  • Fuel
  • Tezro
  • O350
  • O300
I managed to reduce price a bit. I have listing here on ebay. Avoiding ebay I can reduce futher 10% of the asking ebay price.

s-l1600 (1).jpg
 
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