#2093

[@kenchilton]

When you said, “goes through the standard process,” you were correct. That is the main reason why this is made in two parts. The battery cannot survive the IR or hot air reflow process. This component was made to fit on the same place on a PCB that its through-hole predecessor occupied and avoided having to use mixed technology with paste-in-hole or selective wave to get the old part in there. It also avoided putting live voltages on the PCB when the board was not installed in a machine - it is allegedly impossible to short out the battery after it is snapped on the RTC SRAM. I worked with Dallas to develop this part for them, because we were one of the major battery backed NVRAM consumers, and we needed this SMT solution.

[@craigs5212]

Back it the day, I had a design with a RTC chip and solder in radial leaded lithium primary cell. I get a bunch of alpha boards back from assembly, all with dead RTC's . Come to find out the stock room decided it would be a good idea to stick all those battery leads into a sheet of conductive foam before putting them on the shelf.

[@romancharak3675]

That HAT fitted with a CR2032 battery holder might be a nicer solution.

[@mikesradiorepair]

Thought you would like these odd little parts. Personally I'm a big fan of the design. Having had to replace the older all in one through hole versions I thought this design at the time was genius. Battery dies, just pop off and on a new SnapHat. You can still buy the battery/crystal SnapHat's. I have had to replace a few of them over the years in printers and it's so much easier. Replaced the one in my own Xerox WorkCentre 5655 just last year.

[@henrikstenlund5385]

I used a lot of these Dallas clocks more than 30 years ago. I still design circuits around a variant of this ST chip. The I2C HW interface and registers are still the same as they used to be. The reason is that this same clock chip was used back in the days in all MS-DOC and then Windows PC's. So the software driver is the same for all computers. The ST chip variant is still in production and is very popular.

[@charlesdorval394]

Oh interesting, I had no idea those were i²c, neat! That gave me some ideas ... hehehe

[@henrybecker2842]

As you said, it does make sense to make the electronics portion of the product compatible with PCB solder flow methods. It also greatly simplifies replacing the battery because there is no soldering.

[@hangup23]

i'd much rather find these suckers inside an old scope than the dallas. would save me a lot of trouble desoldering large DIP packages from a very old board which is always a bit risky. so i'd say yes, this is definitely a solution to a problem.

[@SX1R]

In the late 1990s I had built a development board with a Dallas Semicnductor 8051, which had battery backed internal SRAM in place of ROM. It was before the days of EEPROM. The 8051 modules were of similar form factor with the memories you showed. They were supposed to keep the program for 10 years.

[@jebricole9084]

We made a lot of design with that chip and Snaphat was also usefull to replace the bat

[@bayareapianist]

Why not just put the battery and Crystal outside like a current design?

[@jercos]

As they say in the DS, this also prevents soldering heat from touching the crystal itself, which can leave it more accurate in the final device without an additional calibration step.

[@monad_tcp]

That's a cool solution, I like not having potted things that are easily serviceable.

[@jameskidd7906]

Sony use this stuff in his hardware like pdw xdcam and pw imx 2000.....as an rtc

[@richardockman5988]

A battery that's easy to replace is always good,Do-hickey is something I remember my dad saying when he couldn't remember the name of something.

[@A3Kr0n]

I have one of those somewhere. It's used in an agricultural weigh scale (Digistar).

[@zexusdexus4193]

Battery backed parallel SRAM (not i2c) is very useful to store values generated in analog circuitry. Yes, I know this sounds like an oxymoron, but if you want to use digital functionality, like encoders and momentary switches, but not have a microcontroller, you have to store state and settings somewhere.

[@mnoxman]

Channeling "Slappy the squirrel" there with Do-Hicky? Add in a "Thing-a-ma-jigg' now and again too?

[@IMSAIGuy]

The word "doohickey" likely originated as US Navy slang in the early 20th century. The first known use of the term was in 1914 in the magazine Our Navy. It's thought to be a combination of the words "doodad" and "hickey".

[@Manf-ft6zk]

I haven't seen real doohickeys before. (I had to look it up.) It reminds me of the old F8 processor with piggy-pack EPROM.

[@Dieseleux]

I have one with snap battery on my Anritsu VNA.... if the battery goes dead or if i change the battery without power on the machine, i lost sram and brick the VNA!!! The battery are stock at digikey.

[@Aleuli73]

On the bright side this is one of the reasons those were quite common and cheap some time ago.

[@Mr.Leeroy]

Makes a great project to make a bus sniffer for live chip to clone it like a jigsaw piece by piece. Unless it fails to read in a boring manner in-circuit while instument is powered down

[@wa4aos]

The problem is like the Dallas chip itself, how long will the battery pack be available. I suspect once the battery fails there will be no replacements.

[@user-qf6yt3id3w]

If it's just a crystal and a battery you could probably work something out pretty easily.

[@radarmusen]

The mk48t08 version is used in mvme cards. A little frustration when the battery is going bad in equipment, causing it to lose the settings.

[@herbertsusmann986]

Definitely a strange part. I guess if PCB real estate is at a premium then you would use this? Otherwise just but a coin cell socket on the PCB next to the chip. Same with the crystal? I can't believe they are selling many of these. Are there second sources for this part? If they are the only mfg then that is a real negative.

[@Mr.Leeroy]

minute per month, imagine how bad this is compared to maybe a second or two a year in a cheapest chip now..

[@sanjikaneki6226]

why not use a RTC?

[@hyoenmadan]

What do you mean? This chip has RTC on it. The only difference with the dallas chip is it having more static ram banks. This is used for firmware which needs big sram to store all the configuration data and licensing blobs. OpenFirmware, UBoot and UEFI need more NVRAM than what is supplied by the legacy Dallas chip, and that's without counting RTOS stuff like VxWorks and such.

[@mikesradiorepair]

It is a RTC. One that you can actually replace the battery on. Just like he described, the earlier versions had batteries that were non replaceable meaning you had to desolder and replace the whole module. With this design the battery and crystal just snap on in the separate "SnapHat".

[@sanjikaneki6226]

@@hyoenmadan ok now i understand, i was thinking of it as a rtc only i never thought it had other data in it + it was super off for me to have a battery in a chip and not in a cheap holder

[@felixcat4346]

Its there so the company can charge an arm and a leg for replacement, and to make it obsolete if they so choose. Evil design.

[@hyoenmadan]

Actually, is worse having all the parts potted together. In this design, you can depot the outer hat only, and check the battery and crystal values without damage the inner chip capsule. And then you can make your own replacement parts in case they kick the replacement hat from the market. You can do the same with the dallas chip, but the process is dirtier, and may require desolder the sh*t if you don't want to damage other parts in the PCB. Also, since this ST clock/sram chip is used generally in instrumentation and/or medical equipment, you may not do your own replacements unless is ABSOLUTELY necessary.