Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Spacedementia87 Newbie Joined: 03/08/2016 Location: United KingdomPosts: 26
Posted: 11:52am 19 Aug 2016
Copy link to clipboard
Print this post
Hi all,
I am new to using the micromite.
The manual states there needs to be a 47uF tatalum capacitor between pin 20 and GND.
I have a boat load of ceramics and Aluminium caps. Can I swap the tantalum capacitor for an aluminium one?
MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209
Posted: 11:58am 19 Aug 2016
Copy link to clipboard
Print this post
A 10uF ceramic X5R works fine.
Datasheet table 30-15 (page 268) states:
A minimum value of 8uF, typical value of 10uF, max is not mentioned.
Capacitor must be low series resistance (1 ohm). Typical voltage on Vcap pin is 1.8v
On page 28 it states that it can be a Tantalum or ceramic capacitor. Curiously enough it states there a series resistance of 3 ohm and a 6v rating.
In practice i always use a 10uf ceramic X5R and it works good. I guess that is the best indicator as datasheets, especially ones that have hundreds of pages are sometimes not very clear or have conflicting information.
Edited by MicroBlocks 2016-08-20Microblocks. Build with logic.
Spacedementia87 Newbie Joined: 03/08/2016 Location: United KingdomPosts: 26
Posted: 12:02pm 19 Aug 2016
Copy link to clipboard
Print this post
Hi,
Thanks for the very prompt response.
Sorry being ignorant here... What do you mean by X5R?
MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209
Posted: 12:21pm 19 Aug 2016
Copy link to clipboard
Print this post
X5R is actually more a temperature range and the change of capacitance in that range.
X = -55 celsius
5 = +85 celsius
R = +- 15 maximum change in capacitance
More importantly with a designator like that it is also a class 2 capacitor which is specifically made for bypass, coupling and decoupling.
Its dielectric also has a low series resistance which in this case is the most important characteristic.
Watch out though, even with the right numbers and codes you need a good quality capacitor. Low quality will still have a series resistance that is too high. Check the datasheet before buying!Edited by MicroBlocks 2016-08-20Microblocks. Build with logic.
Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9642
Posted: 12:41pm 19 Aug 2016
Copy link to clipboard
Print this post
Standard aluminium electrolytic is NOT recommended, as they are not low-ESR type as MicroBlocks mentioned.
Vcap is vitally important, as it stabilises the internal PIC32 core voltage regulator, and a bad choice here can(read: will!) cause stability problems and only cause you headaches with odd system behaviour like sporadic crashes and reboots or other unpredictable nasties.
Tantalum type are fine - the recommended value of standard through-hole tantalum cap 47uF 16v, or the aforementioned 10uF X5R MLC SMD(multi-layer ceramic surface-mount-device).
So, in a nutshell, NO - do not use standard aluminium electrolytics for Vcap.Edited by Grogster 2016-08-20Smoke makes things work. When the smoke gets out, it stops!
Spacedementia87 Newbie Joined: 03/08/2016 Location: United KingdomPosts: 26
Posted: 12:45pm 19 Aug 2016
Copy link to clipboard
Print this post
Ahh OK,
I will not use an aluminium cap then!
I don't know whether my ceramic caps are X5R or not.
They are generic ceramic disc caps. Any way of finding out?
Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9642
Posted: 12:55pm 19 Aug 2016
Copy link to clipboard
Print this post
Hey there.
No way of knowing UNLESS you have the datasheet for the caps you have.
They don't generally make disc type ceramic in 10uF that I have seen, but I just may have not seen the ones you have.
If in ANY doubt, best to swap for a 47uF tantalum type, as they ARE one of the recommended type, and you really, REALLY don't want to spoil your first Micromite experience with buggy behaviour due to a bad Vcap choice. Smoke makes things work. When the smoke gets out, it stops!
MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209
Posted: 05:12pm 19 Aug 2016
Copy link to clipboard
Print this post
10uF ceramic disk capacitor or higher is ok. Just make sure the type is class 2.
If you are not sure and can not find a datasheet, better buy some through hole tantalums 47u. Make sure you mount them the right way as tantalums have polarity.
As Grogsters said, you really don't want unreliable behaviour. It will drive you nuts as on the strangest moments the software will crash.Microblocks. Build with logic.
Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9642
Posted: 06:01pm 19 Aug 2016
Copy link to clipboard
Print this post
...and that will ruin your first Micromite impression, and first impressions last, so we don't want you to have to go through that. Smoke makes things work. When the smoke gets out, it stops!
Spacedementia87 Newbie Joined: 03/08/2016 Location: United KingdomPosts: 26
Posted: 09:37pm 19 Aug 2016
Copy link to clipboard
Print this post
Thanks for all the help.
I do find it a little surprising that in 2016 tantalums are a requirement considering their bad reputation.
I have found d some for reasonably cheap so I will order just in case.
If the ESR is the main concern as the micromite manual suggests I would have thought any old ceramic would be of as their ESR tends to me in the mOhm range.
Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9642
Posted: 09:51pm 19 Aug 2016
Copy link to clipboard
Print this post
Ceramic IS preferred, provided it is at least X5R type.
Ceramic provides the low-ESR requirement, and the X5R dielectric provides the stability. Non-X5R type ceramics could potentially drift 20% or more in value depending on temperature conditions, whereas X5R are stable over a wide temperature range. X7R are OK too, so I belive, but I do seem to recall reading one member here had issues with X7R too, so it is best to stick with X5R to be sure.
One reason why the Tantalum value is four times the capacitance value of the ceramic one is to allow for tolerances in the tantalum caps you might choose to use.
"Any old ceramic" DOES do the low-ESR part of the equation, but you need low-ESR and high stability or tolerance so that the capacitance stays put under different temperatures. Low-ESR is only half of the requirement.
I always use ceramic MLC's on all my boards, with the cap as close to the Vcap pin as possible.Edited by Grogster 2016-08-21Smoke makes things work. When the smoke gets out, it stops!
Spacedementia87 Newbie Joined: 03/08/2016 Location: United KingdomPosts: 26
Posted: 10:11pm 19 Aug 2016
Copy link to clipboard
Print this post
Ok I see.
Is it me or are X5R ceramics difficult to find as through hole components?
Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667
Posted: 10:48pm 19 Aug 2016
Copy link to clipboard
Print this post
Yes,
And you end up building Monsters to control everything conceivable...
Then look for more new ideas.
WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2948
Posted: 11:28pm 19 Aug 2016
Copy link to clipboard
Print this post
@Spacedementia87
If you want to contact me I can send you a couple of 10uF ceramic thru-hole caps.
By the way, one thing I used to do a lot (on 28-pin DIP MicroMites) is solder a 10uF ceramic SMD cap between pins 19 & 20. This results in a self-contained 'plug-in' module requiring only power.
WW
Spacedementia87 Newbie Joined: 03/08/2016 Location: United KingdomPosts: 26
Posted: 11:32pm 19 Aug 2016
Copy link to clipboard
Print this post
I have loads of 10uF ceramic through hole caps but everyone here seems to say that they are no good unless X5R.
No online suppliers seems to have X5R through hole caps.
WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2948
Posted: 11:38pm 19 Aug 2016
Copy link to clipboard
Print this post
These thru-hole MLCCs are indeed specific to MicroMites (sorry - I should have said that I have used these on literally hundreds of MicroMites!!)
They are X5R parts, and I have both 0.1" and 0.2" lead pitch.
If still interested then PM me (or email me - address in 'signature')
Spacedementia87 Newbie Joined: 03/08/2016 Location: United KingdomPosts: 26
Posted: 11:41pm 19 Aug 2016
Copy link to clipboard
Print this post
Ahh OK. I have actually ordered some tantalums now. But can I ask where you have got them from?
I have not managed to find any!
Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9642
Posted: 11:41pm 19 Aug 2016
Copy link to clipboard
Print this post
Yes, the through-hole X5R ceramics ARE much harder to find then, say, an SMD equivalent, which are easy to find.
WW will be able to help you out in your through-hole quest! Smoke makes things work. When the smoke gets out, it stops!
WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2948
Posted: 11:44pm 19 Aug 2016
Copy link to clipboard
Print this post
I have a good friend in Electronics assembly and he sourced me some (well hundreds actually) at a reasonable cost. I knew that I would need many so it was worth the investment.
I am sure someone like DigiKey will have an equivalent - just a matter of searching time!
WW
robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2447
Posted: 12:31am 20 Aug 2016
Copy link to clipboard
Print this post
i'm going to break with the trend and admit to using garden-variety 10uF leaded ceramic capacitors off ebay without any issues. if the concern is the drift in capacitance over the intended operating temperature range, one could always go for 22uF leaded ceramics.
and keeping the component within 1/4" of the PIC32 is quite important. while soldering an SMD part between pins 19 and 20 on the DIP package sounds like a good idea, be wary that when inserting the PIC32 into a socket you risk cracking the capacitor.
another major problem folks have struck in the past is with less-than-perfect solderless breadboards leaving the connection to Vcap dodgy. it is very important that all ground pins are securely connected together, and that all Vcc and AVcc pins are securely connected together.
cheers,
rob :-)Edited by robert.rozee 2016-08-21
Page 1 of 2
Print this page
The Back Shed's forum code is written, and hosted, in Australia.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Print this post
