SMD Heatermeter on a RPI B+? Yes, it can be done......


 
Peter F

Peter F

TVWBB Fan
These boards are based on the work that John Bostwick has done on his design for a SMD version of the heatermeter. John was so kind to send me his Eagle files and I used his files as the foundation of this design.

The main difference is that this is a 4 thermistor version. Also the complete routing is changed, groundplanes are added and some components have been moved.

I love the white PCB's although they have one huge drawback, they need to be cleaned much more thoroughly than darker boards.
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All SMD components bottom side.
HM5.0%20SMD-2.jpg


All SMD components top side.
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Bottom finished.
HM5.0%20SMD-4.jpg


Top finished. The display will have to move to the bottom side of the board, but this is a prototype board and the display is much easier to remove this way if the board turns out to be a dud.
HM5.0%20SMD-5.jpg


And yes it fits...... but only when you cut the 14 extra pins off the RPI header.
HM5.0%20SMD-6.jpg


Succes! The HM booted up first time and all seems to be working just fine. Tomorrow I will do a test run but so far I'm a very happy camper.
HM5.0%20SMD-7.jpg



Bryan and John, thanks for the excellent work!
 
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Looks good. I like the white board. How did ya like soldering the atmega. Definitely easier when no vias are near it. Glad you were able to get it up and running.
 
I have used solder paste and a hot air soldering station for the smd parts, this works real easy. The vias underneath the atmega are moved closer to the center to fix some clearance issues so they didn't bother me at all while soldering.

I love soldering with hot air, it is almost magic when you see the parts aligning themselves.
 
I have been playing with the board layout and I think I will go for this version;

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Pros;
- Four individual buttons instead of the 4 way navigation switch. I can't find the SKQUAAA010 anymore for reasonable prices so 4 buttons are the way to go.
- It's a combined TC and thermistor board, just like the original.
- Hole spacing is compatible with V4.2.4, makes it easier to design a case.
- Better layout of the components, less vias required.
- Should fit a RPI B+ without trimming the RPI header.

Cons;
- Doesn't fit in any of the current cases.
 
I think Peters board looks like a winner.

Atleast, it gives people an option to go the through-hole route, which is much easier for the beginner, although more expensive and a smd version that is cheaper to make and smaller but for more advance solderer or someone who wants a challege.

These boards can work with all version of the Raspberry pi, except the Rpi 2, but the case would need to be wider to accommodate the various board differences.
 
looks good.

I'm waiting on a case from Tom for the version I had done. After I receive it, I will post a picture of it in a case. I have also donated it to someone in Florida
 
Looks real good. The SMD board certainly makes the HM board look sparse...

Though I am not fond of SMD soldering, after having done so much on the thermocouple amps this board looks pretty doable. I wasn't in love with the "all SMD" idea to begin with, or having the power and CAT5 jack on the bottom (again), but I have never set my HM on end so the bottom jacks are a non-issue (to me) and the sparse nature of the board makes the soldering look less daunting (at least to someone that has done a bit of SMD).

So you guys are kinda winning me over! I don't think the SMD version should be the ONLY version of the HM available, but looks like a nice option for someone with a bit of experience with electronics.... and it certainly presents opportunities to expand the HM capabilities with stuff like more TC amps and using the extra pin on the SMD ATMega for something... Nice job guys!
 
Yeah, they are not as bad as one may think they are to solder. Actually, they are much faster to solder. The atmega chip can be a problem for the first timer, as its a pain to get lined up correctly, and magnification is a must. But after a few times its not any harder then the tc amp.
 
It would be REALLY nice if those SMD chips had some sort of alignment peg or something that could help guide them into the proper place, sometimes they go so easily and other times they just wont cooperate...
 
Well, if you use hot air or a reflow oven, SMD parts basically self align. They're really not meant to be installed with a soldering iron.
 
I'm sure you're right, but it seems reflow ovens are a couple hundred bucks...
Though I really haven't made the slightest effort to tool up for SMD soldering, didn't even get a soldering iron with a special small tip or anything. I was kinda trying to see if the average guy could actually do the work (TC amp) with regular tools you can get at radio shack or whatever (btw, my local radio shack isn't dead yet, I think they are selling plenty of phone contracts so the doors are still open....) If you tool up properly for the SMD work I guess it may go pretty easily...
 
I have been thinking of ways to make it easier to align the parts but have not thought of a good way yet. Been also thinking of getting a toaster oven and solder paste and then getting a stencil made.
 
I just watched a video of hot air soldering with solder paste, pretty cool, but it's still not a piece of cake to align chips with a lot of legs when done that way either. I see cheap part grabbers that could help a bit I guess.
 
Have you looked into Schmartboards? I've used a few to convert smd to dip and the are really easy to solder. I don't know how much it would be to set up a custom board though.
 
I just looked over the schmartboard speel, the canals on the traces of SMD chip legs looks like it would do the trick for alignment, but designing the whole board out of schmart modules might be a costly PITA. Would be nice to have a module with the SMD ATMega, shift register and TC amp on it, so it would be easier to place/solder those chips, then solder the larger legs of that module onto the HM board. But again, the cost is what I wonder about....
 
Yeah the easy way to do it is solder paste and a toaster oven. The thermocouple amp is a pain because the pins don't get enough solder to really grip the chip, but everything stays in place once you place it. The 0805 parts I don't even have to release the suction because they just get pulled off by the paste.

For one-off boards. I just put solder on one leg of the chip pad. Place the chip on it and touch so it is tacked down, then twist the chip if it is off kilter, hold it down, and touch the leg again. When the joint cools it isn't going anywhere so soldering the rest is super easy.
 
version 1 of the case is almost ready, there are still some rough edges but nothing that can't be fixed in a day or so. Unfortunately further work on the case will have to wait until I'm back from Saudi Arabia.

HM5.0%20SMD%20Combi-4.jpg


HM5.0%20SMD%20Combi-5.jpg


HM5.0%20SMD%20Combi-6.jpg


Many thanks to Tom Kole for letting me use his design as a base for this case.
 
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