Electronics > Projects, Designs, and Technical Stuff
Yet another resistance decade box
ez24:
whew
Just did my first board. First time with these really small SMDs. Like training fleas.
It is a really bad job. The resistors are sticking up at all angles so no pics. |O
I snapped in the board with no problems and it holds strong. Checked with a meter and it works :-+
Just curious there are 10 resistors. Is the 10th resistor an extra? I think I am counting right?? I just have tweezers and a cheap 25w iron and reading glasses. No fancy stations.
Shaking now so I will have to wait until tomorrow and try another one. I started with the 100k set.
I would like to know if I need to tin the pads fist before I try another one. Tinning the pads makes the resistors not lay flat. How about tinning one pad so the solder makes it stick flat, by pushing down with the tweezers while soldering, then solder the other end without tinning it?
Going to order another set of switches tonight.
Good job, how many people worked on this job? Thanks Fortran
thanks
LeonV:
Got the boards + resistors yesterday :-+
All the way in New Zealand.
Now to buy the pushwheels..
Will try these:
http://www.aliexpress.com/item/Black-18mm-x-6mm-0-9-Digits-BCD-Code-Pushwheel-Thumbwheel-Switches-KM2/1804257049.html
But will need to save up, so wont be too soon.
Fortran:
--- Quote from: ez24 on July 28, 2016, 01:05:10 am ---Just curious there are 10 resistors. Is the 10th resistor an extra?
--- End quote ---
Yes the 10th resistor is extra. In case you flick one off the table :)
The 0.1% strips are only 9 though, because of the much higher price.
Tinning one pad and sticking down the resistor before soldering the other pad is a very good way to do it.
Using only an iron you might want to use as little solder as possible just to make it stick, then come back after soldering the other side and just touch it up with some fresh solder to make it flow nicely.
Heating too long makes the joint lumpy and ugly.
If you're ordering another set, let me know if you want me to solder it for you.
Two people worked on this.
PeterZ drew the board and posted the design files, and I ordered them in enough quantity to make them affordable for everyone.
ez24:
Tried another board by tinning one contact. Had a 7 out of 9 failure rate. I could be only the "3" digit, in other words only 1 and 2 work.
My 4 power glasses are not powerful enough so I cannot see if I have a cold joint nor do I know which one is the third digit.
Also the board would not snap in, is was too wide. I solved this by making a very small bevel with a razor blade and it snapped in. So for now on I am going to make a small bevel on the switch and on one side of the circuit board.
It might be possible to do one contact at a time if I had a small tip and solder. It is very hard to get in to solder (the ends) with the large (used to be small, I think 1/8") iron that I have. So I will go back to tinning both pads first and put up with tilting resistors. If it is good enough for the Italians it should be good enough for me.
Also it is good to have an extra resistor. One stuck to my iron and dropped as I moved the iron. These things are so small they evaporate as they fall through the air.
Has anyone come up with a trouble shooting guide using via to via resistance readings? I cannot see the traces. In other words how can I find No. 3. I am wondering if there is a No. 3 ? I wonder if it depends on how the switch goes together. In other words maybe 3 one time but 5 the next time??
thanks
Fortran:
You shouldn't need to trim anything to make it fit the switch, but I guess there may be slight variations in batches.
I found that pressing down firmly right next to the pilot holes using a 5mm wide flathead screwdriver worked really well.
If it still won't cooperate you can try sanding the edges a bit.
Attaching a layout of the board.
If you have problems with No. 3, you probably have a solder-bridge to the via that goes underneath it.
Check if it's shorted.
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