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RTC SUPER CAP WIP

Posted: Mon Aug 28, 2017 10:03 am
by rubber_jonnie
I now have all the bits for a little project suggested by Chris, which uses a super capacitor rather than a battery.

In the picture below, are all the relevant bits.

Circled in yellow are the parts for the external card, circled in red is one of my original RTC prototypes, and circled in blue are the super capacitor and supporting parts.

Image

I'll report back when I've had a chance to put it all together. Either that or have a room full of magic smoke and scorched components!!

Re: ST RTC EXTERNAL BETA - WIP

Posted: Mon Aug 28, 2017 5:34 pm
by exxos
rubber_jonnie wrote:
Mon Aug 28, 2017 10:03 am
I'll report back when I've had a chance to put it all together. Either that or have a room full of magic smoke and scorched components!!
Do you know what to do with it all, thats the question ;)

Re: ST RTC EXTERNAL BETA - WIP

Posted: Mon Aug 28, 2017 11:27 pm
by rubber_jonnie
exxos wrote:
Mon Aug 28, 2017 5:34 pm
Do you know what to do with it all, thats the question ;)
So the cartridge port and clock, yep, I'll do that first, because I'm pretty sure I won't have an issue there :D

As for the super capacitor bit, we'll I'll build based on your schematics, then add the two together when I'm confident it works :?

Oh, and I'll ask you for a hand if I can't suss it out!

Re: RTC SUPER CAP WIP

Posted: Mon Jan 15, 2018 11:04 pm
by rubber_jonnie
Well, I've not had a great deal of ST time due to family stuff, so very behind on this thread at the moment.

However, the last month or so has been good, and I have caught up quite a bit.

I now have the external clock cart built and working, and I'll be testing it this week. I used a proper RTC board in the end, rather than my proto board devices, as I wanted to avoid too many wires.
IMG_20180115_223859.jpg
IMG_20180115_223859.jpg (4.53 MiB) Viewed 1208 times
Intial testing is looking good though, with time keeping nicely even when unplugged. Many thanks to exxos for all his support in this process.

Next step is to build the circuit for the supercapacitor and see if it works :D

Re: RTC SUPER CAP WIP

Posted: Tue Jan 16, 2018 8:28 am
by Petari
Super capacitor - I remember them from video recorders . Capacity in range of 1 farad ? How long it can supply clock chip (when no power) ?

Re: RTC SUPER CAP WIP

Posted: Tue Jan 16, 2018 8:39 am
by rubber_jonnie
Petari wrote:
Tue Jan 16, 2018 8:28 am
Super capacitor - I remember them from video recorders . Capacity in range of 1 farad ? How long it can supply clock chip (when no power) ?
I'm at work, so can't check, but I think it is 5 farads. Speaking to exxos, if I recall correctly, I seem to recall that the thinking was something like 6 months, the DS1315 has a very small current draw, so I can imagine it would happily work that long.

Re: RTC SUPER CAP WIP

Posted: Tue Jan 16, 2018 11:27 am
by exxos
rubber_jonnie wrote:
Tue Jan 16, 2018 8:39 am
I seem to recall that the thinking was something like 6 months, the DS1315 has a very small current draw, so I can imagine it would happily work that long.
I forgot about this project :)

6 months was theoretical based on current draw (according to the datasheet of the RTC IC)...

... but I did not take into account the self discharge (internal resistance) of the super cap.. which has a similar "draw" to the IC itself.. unfortunately this means the likely best result would be 3 months :(

Re: RTC SUPER CAP WIP

Posted: Tue Jan 16, 2018 11:35 am
by rubber_jonnie
exxos wrote:
Tue Jan 16, 2018 11:27 am
rubber_jonnie wrote:
Tue Jan 16, 2018 8:39 am
I seem to recall that the thinking was something like 6 months, the DS1315 has a very small current draw, so I can imagine it would happily work that long.
I forgot about this project :)

6 months was theoretical based on current draw (according to the datasheet of the RTC IC)...

... but I did not take into account the self discharge (internal resistance) of the super cap.. which has a similar "draw" to the IC itself.. unfortunately this means the likely best result would be 3 months :(
Ooops, never mind, still worth trying to see how it goes. Will be in touch soon Chris, need to have a quick chat re the schematic.

Re: RTC SUPER CAP WIP

Posted: Fri Jan 19, 2018 10:09 am
by exxos
rubber_jonnie wrote:
Tue Jan 16, 2018 11:35 am
Ooops, never mind, still worth trying to see how it goes. Will be in touch soon Chris, need to have a quick chat re the schematic.
If you have a benchtop variable power supply, you could just simply charge the super capacitor or to 3.6V (I think ?) Whatever is the maximum allowable between the super And the RTC IC ... Then just solder it across the battery contacts one of your cartridges for example. Then set it, and try and remember to check the voltage on the capacitor once a week and make a note of it..

Circuit I gave as a example, charging it up when the ST was turned on, we would have to disconnect that to stop it charging the capacitor each time machine was turned on..

EDIT:
Even something simple like https://www.aliexpress.com/item/LM317T- ... 52269.html would be useful. Looks like it has a multi turn pot, so should get good accuracy with it.

Re: RTC SUPER CAP WIP

Posted: Fri Jan 19, 2018 1:59 pm
by rubber_jonnie
exxos wrote:
Fri Jan 19, 2018 10:09 am
Even something simple like https://www.aliexpress.com/item/LM317T- ... 52269.html would be useful. Looks like it has a multi turn pot, so should get good accuracy with it.
Hmm, interesting....