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Forum Index : Microcontroller and PC projects : MicroMite 44 Pin TQFP Eval PCB/Module
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| WhiteWizzard Guru  Joined: 05/04/2013 Location: United KingdomPosts: 2817 |
Hi Don, Great to have your feedback! Regarding the single 5v (out) pin, I originally had 2 rows of 23 pins with this 5v pin on the top left (pin 46) along with a ground pin on the bottom left (pin 1). However this made identifying the correct PIC pins a little confusing (e.g. DIP pin 1 = 0v, DIP pin 2 = PIC pin 1 . . . .DIP pin 45 = PIC pin 44) and hence felt it better to directly simulate a 44 pin DIL package with each DIP pin matching the PIC pin number. (Have I lost you yet?). However, I thought the 5v input from the USB socket should be made available to the user so included it on the module as shown. All this said, I do think it is worth adding a ground here to make it a two pin header. Perhaps even a three pin header and include 3v3? What do you think? - like you say this avoids having to 'chase' the correct pins for power. It wasn't intended as a power input but yes it could be. However I wouldn't currently recommend this as I haven't included any protection in case something is also plugged into the USB at the same time. Do you mean why not 6 pins? If so then the reason is I have never had a requirement to use Pin 6 so hence didn't include it. Is there a reason you think I should include pin 6? OR are you asking why its there? If so, then obviously it is to update firmware whenever Geoff sends out updates. Regards, Phil For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9309 |
Looks very nice, Wiz - well done, mate! 
I've had a rummage, and have found about 100x 10uF X5R 6.3v ceramics in 1206, so these will do very nicely, and according to Geoff, I can use these, so great. 
Smoke makes things work. When the smoke gets out, it stops! |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Lads, With the LOW ESR Cap (47uf) I cheated when I built my uMite as, whilst I bought some Low ESR 47uf SMD Caps) I built my uMite onto a breadboard with plug in wires on a 40 Degree (Celsius) day and didnt wish to crank up the soldering iron just to solder legs onto the SMD cap to plug into my breadboard so I just plugged a 100uf Electro into the breadboard and away it went.. Not that I intend to use a 100uf electro but it didnt stop the uMite from working so I dont think it is as critical as they make it out to be.. Of course I will use the correct cap when I built my more permanent test rig. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
Thanks Phil, To save you quoting me, quoting you, I'll start with a clean slate.
If you can make it a 3 pin header for power, yes that is even better. However you may have to move the LEDs together, or something similar to make room for the header. I'll assume there will be a small assembly text file, and schematic to go with the files, so I would make it voltages out only, and mention it could be used as voltages in, if the USB input isn't used. Mind you, I would expect that the user would be familiar enough with the board and schematic to be able to configure what he wants/needs for development, or the final application. Re the 6 pin header, sorry I should have enlarged the question enough to make it fully understandable. PICkit 2, and 3 is a 6 pin header, (as are the clones) so I felt there would be less confusion if you placed a 6 pin header there, even if the 6th pin isn't used. Which bring me to my final point: Text. Will you have a text overlay? It needs a "1" near pin 1 of the 44 pin DIP socket, and "1" near pin 1 of the ICSP socket. When it is being manufactured by a factory, or an individual, it is only built once, so other text such as LED polarity will generally be obsolete after being manufactured. If you find room for text, then place as much as you can on either side of the board. Even if it just says "+", "G", "5", "3". It will all help. Cheers Don... https://www.dontronics.com |
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| JohnL Senior Member  Joined: 10/01/2014 Location: SeychellesPosts: 128 |
Be very careful choosing ceramic SMD capacitors. Read data sheets very carefully. They come in different performance varieties. Many are unstable over V DC. Check capacitance at your working voltage carefully. Link to voltage coefficient info., Temperature coefficient can also be important http://www.niccomp.com/help/VoltageCoefficientofCapacitors-0 32012-R1.pdf |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2817 |
Don, Great suggestions so will work on them straight away. Note: I will probably leave 5 pins for the ICSP due to space limitations; but will clearly indicate ICSP Pin 1 Will update when complete . . . For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9309 |
Never had any issues before. I would fully expect any SMD cap to get upset, if you exceed it's voltage rating - that's pretty standard not just for the SMD ceramics, but just about any cap I can think of. 
Smoke makes things work. When the smoke gets out, it stops! |
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| JohnL Senior Member Joined: 10/01/2014 Location: SeychellesPosts: 128 |
Grogster, My point had nothing to do with exceeding the voltage rating of caps. Y5V caps can have 10% of their stated value at their full working voltage. 10uF 6.3v Y5V SMD ceramic cap can have more than 80% variation in capacitance over its WORKING!! voltage range. Look at the link I posted above. 
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9309 |
Link not valid. Spat back a 404 not found for me, anyway... Can you please repost the link, and put it up as a hyperlink - not just as text. Thanks. Smoke makes things work. When the smoke gets out, it stops! |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6103 |
It's the old "put an extra space in the text" problem. Remove the space in "032012" and all will be well. Jim VK7JH MMedit MMBasic Help |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9309 |
Ahhhh - I see. This is why links need to be hyperlinked in the first place.
So, the link should be: Capacitor link EDIT: Very interesting PDF. I'm surprised that this info has not lead to lawsuits, as the cap is listed as 1uF 16v, but it clearly ISN'T! 
I will study this a bit more, but in all the SMD ceramic caps I have used, I have never had any problems. PROBABLY as I use 100n the most, and these are normally decoupling caps on LDO regulators, within about 1mm of the regulator itself, and then I tend to supplement these with more standard electros in the area of 220uF for input and 100uF for output - might be why I have not had any issues? Not sure, but the PDF makes interesting reading. Smoke makes things work. When the smoke gets out, it stops! |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2817 |
Hi JohnL, With your knowledge about caps, can you please take a look at this one: TPSB476K006R0250 (RS Components: 547-9984) It's a 47uF tant (not ceramic!) rated 6.3v with low esr. I have used this one in several MicroMites and never had an issue so far. Would appreciate your thoughts & advice - please feel free to recommend a more suitable alternative! Regards, Phil For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9309 |
Yes, I am also seriously looking at dropping my use of the 10uF X5R's I have here, for some tantalum versions. Do post back, John! Smoke makes things work. When the smoke gets out, it stops! |
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| JohnL Senior Member Joined: 10/01/2014 Location: SeychellesPosts: 128 |
Guys, I came across the SMD ceramic cap information some time ago as a surprise. I had previously assumed that capacitor tolerance levels are reasonably stable within the working voltage. Ceramic caps are still better for decoupling applications and the trick is to select the capacitor with HIGHER maximum operating voltage. This will generally give you the guaranteed stated value at its lover operating voltage that falls within your circuit design. Best is to look at a data sheet for a specific brand and stick to reputable manufacturers. Even the most reputable brands of SMD caps are very cheap from reputable places like Mouser, Element14 etc. Again I am no expert on tantalum caps either, but apart from spec differences tantalums have had reliability and longevity issues similar to electrolytics. |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2350 |
i suspect the situation with ceramic capacitors is more complicated that at first appears. note that the testing discussed in the pdf is being conducted under AC signal conditions. if we charge up any capacitor with a DC voltage, as that voltage ramps up the capacity can not significantly drop without violating a few fundamental laws of physics. what is more likely happening is an effect based upon the ability of charge to migrate within the ceramic capacitor. when a sudden load is applied the charge located within a given region is depleted first, and the charge from other regions can only move to 'fill the gap' at a limited rate. this is quite different from ESR, as no heat will be produced in the migration. and it can also not fairly be described (strictly speaking) as reduced capacity, as the energy is stored and can be retrieved, albeit more slowly than one might desire. while not a reduced capacity at higher voltages, it is an effect that still behaves exactly like this for all practical purposes. i've quite often seen designs where up to three ceramic capacitors of 100:1 value differences are paralleled up. for instance, close together and in parallel one sees a 10uf, a 100nf, and 1 1nf ceramic capacitor. each one supplied current in turn, first the 1nf and finally the 10uf, providing an even discharge. so, paralleling up several ceramic capacitors might be a good bet in the 32mx150 case. rob :-) |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9309 |
A bloody surprise to me, mate. I always thought that ceramic caps were pretty stable on the whole. Although, that is based on my experience with DISC ceramic through-hole caps, and I have no doubt that 100p disc caps in RF applications really work as they are supposed to. But with the higher values, it would seem there really is a concern with the capacitance drop-off as the voltage increases, going on the graph in the PDF. ...really quite shocking for me... I always selected ceramic SMD caps based on their value and voltage, ASSUMING that the capacitance would be ball-park at the rated voltage. Now it would seem I am wrong on that one - bloody hell! Smoke makes things work. When the smoke gets out, it stops! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9309 |
WOW - that is a really good electronic response. Thanks. Very useful information. As I am not, nor have I ever, used SMD ceramics on AC, it is always DC, does that change the graphs in the PDF significantly? I also wonder - the PDF, although very informative, is targeted such that they want you to buy THEIR caps... (not that I am dismissing the information in the PDF, just wondering how much of this is marketing) Smoke makes things work. When the smoke gets out, it stops! |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2817 |
Hi all, Based on Don's feedback I have slightly modified the top PCB. This is a pre-etch photo to show the following: * Pin numbers (equate to PIC pin numbers) * Group of three power output pins labeled 0v, 3.3, 5v (lower left corner) * Pin 1 identity on ICSP * Date flow direction 'arrows' next to coms LEDs (Rather than say Tx & Rx which can get confusing depending upon from PC of from MicroMite's perspective) The numbers are about the same size as the small numbers found on a breadboard. I don't want them too big - just big enough so you can go straight to 'pin x' without having to (mis)count pins. 
I will etch this in the morning as it's too late now. In the meantime please let me know about any more suggestions you may have! Regards, Phil For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2817 |
Hi All, In a rush to get something available to you all, please find below the file required to allow you to create your own PCB for the 44pin MicroMite. 2014-02-10_004139_MicroMiteDIPv2.brd.zip It will create a 44 pin DIP allowing you to use it in a breadboard in a similar way you would use a 28pin PIC (but obviously with all the extra I/O pins). 
To clarify, this isn't the file to create the more advanced Eval PCB/Module which I am now finalising the design. So for those of you who don't currently have the ability to test Geoff's software for the 44pin MicroMite; i.e. if you don't currently have any TQFP adaptor board, or you are still awaiting delivery, then why not have a go at building this simple PCB! This is an EAGLE .brd file from which you can print out the artwork for the single sided PCB. If you don't have EAGLE you can download a light version for free from the following link: Free EAGLE download Hoping this will prove useful to some of you. Regards, Phil For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9309 |
Thanks, Phil. 
This saves me having to design something similar. Smoke makes things work. When the smoke gets out, it stops! |
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