TheBackShed.com

Forum Index : Microcontroller and PC projects : SD Card and brown outs

Author

Message

akashh
Senior Member

Joined: 19/01/2014
Location: India
Posts: 115

Posted: 03:38pm 20 Dec 2015

Copy link to clipboard

Print this post

I have been having issues with brown outs or incorrect power up that seems to put sd cards in an indeterminate state. I am facing this issue with the Wattmon but I assume the same would apply to all MM devices, and as far as I can tell there is no way to re initialise the card without a physical power cycle. It also happens sometimes when a load is applied to the output of my device which drops the power supply below acceptable limits for a brief moment. I have a watchdog on the processor that reboots it so the firmware never locks up but apart from adding a mosfet to the vcc or gnd pin of the sd card (not yet done) I haven't thought of anything else to try. Does anyone have any ideas?

Akash

Grogster

Admin Group

Joined: 31/12/2012
Location: New Zealand
Posts: 9643

Posted: 06:55pm 20 Dec 2015

Copy link to clipboard

Print this post

Hi.

You could try an RC filter on the power line to the SD-card.
Say 10R in series with the supply, and 22uF across the SD card and ground.

Generally speaking, should not be needed if the master PSU can indeed do the current you are trying to draw from it, and the output has enough decoupling caps on it.

The fact that you say you have momentary voltage dips under load, makes me wonder about the stability of the PSU that is feeding everything. I don't know what you are using PSU wise, but always use a quality PSU for this kind of thing. There have been threads over the years with all sorts of odd things happening, and it was found to be cheap plug-packs that are not able to offer a stable voltage under some load.

I'm not saying you are using one of those, but I feel I should mention it.....

Smoke makes things work. When the smoke gets out, it stops!

akashh
Senior Member

Joined: 19/01/2014
Location: India
Posts: 115

Posted: 03:53am 21 Dec 2015

Copy link to clipboard

Print this post

Hi Grogster,
Thanks for the info. I could give that a shot, I think I do have a cap already with inductor. However, in Indian conditions brown outs are not uncommon, and voltage can dip to very low levels and then bounce back, this has reset the pic but somehow not the sd card, it stays in a kind of frozen state, and I have seen this more than once. I just thought I would post it here to see if anyone else was facing similar issues.

Akash

robert.rozee
Guru

Joined: 31/12/2012
Location: New Zealand
Posts: 2447

Posted: 05:37am 21 Dec 2015

Copy link to clipboard

Print this post

one solution, when working on a bench setup, is to have a lead-acid gel cell battery with a float charger permanently connected, that sits at the back of your bench for powering projects you are working on. 13.4v for a 12v battery, or 6.7v for a 6v battery. this is assuming gel cells are readily/cheaply available in india.

another option is to use the 5v output from a laptop USB port. this is what i do most of the time, as i'm usually wanting serial connectivity anyway.

cheers,
rob :-)

Grogster

Admin Group

Joined: 31/12/2012
Location: New Zealand
Posts: 9643

Posted: 12:16pm 21 Dec 2015

Copy link to clipboard

Print this post

Hi.

I did not realise that it was your mains dropping/dipping out - that changes things.
Even the best PSU in the world could not really help you out of that situation.

Good suggestions there from Robert.

I prefer the gell-cell idea, and this is exactly how we do some solar paging sites - trickle the battery via the solar cell and charger during daylight hours, but the battery supplies all the current for the pager transmitter - even during the day.

A little 7AH battery would probably be plenty for anything you could want to power.

It would be a good idea to use a current-limited PSU if you use the float battery idea, as even a small gell-cell can provide some serious current into a fault!

Smoke makes things work. When the smoke gets out, it stops!

akashh
Senior Member

Joined: 19/01/2014
Location: India
Posts: 115

Posted: 02:59pm 21 Dec 2015

Copy link to clipboard

Print this post

Thanks for the suggestions guys!
For the existing devices I may have to go that route but I was thinking to implement the mosfet idea I mentioned earlier to reduce cost, since that is less than a dollar.
All devices have a one amp fuse and ptc on board so that should help against shorts.

Print this page

To reply to this topic, you need to log in.