I have never created a KiCad Footprint before. I am trying to modify the builtin Buzzer_12x9.5RM7.6 (from the Buzzer_Beeper library) to fit another buzzer which I have bought. You can find its datasheet here:
I would like to put a screenshot of the dimensions from the datasheet but as I new user I can only put one image in this post.
I believe that I got the distances between the holes correct. However I am very unsure what the hole size should be. I see several different suggestions online.
First, to me the datasheet seems to look like the pins (on the buzzer) should be round, but they are actually more oval in the unit I received.
Here is a picture to illustrate what I mean (no I do not have a better camera than this) (yes I bent the inner pin (one closest to image top)):
The footprint I “created” by shamelessly copying Buzzer_12x9.5RM7.6 still uses round holes though.
I have currently chosen to stick with the hole size that Buzzer_12x9.5RM7.6 is using - 1mm. This is based on this reasoning:
The pins have a diameter of 0.6+/-1mm according to the datasheet. That gives me 0.7mm “worst case scenario” diameter.
Now, my PCB manufacturer, JLCPCB, says that their capability for through-hole drill diameter is: “+0.13/-0.08 mm”. So that makes the worst case add up to 0.83mm.
Then we go back to the datasheet which says that the tolerance for all other measurements are +/-0.5mm. So worst case the center point of the pins are actually 5.5mm apart from each other. Therefore I should add 0.5mm to the radius / 1mm to the diameter. That is 0.93mm.
0.93mm… let’s just round that up to 1mm. I then realize that I arrive back at the very same diameter that Buzzer_12x9RM7.6 (which I am modifying) also uses.
Is this reasoning valid? Or will I face problems during production?
I understand what you write as they can make hole bigger by 0.13 or smaller by 0.08. If from it you try to estimate what diameter you should specify than to your 0.7 you should add 0.08 and not 0.13.
Read this:
to find how to promote yourself to be able to add more to your post.
There are elements with square pins and still footprint uses round holes.
Simple questions: how many are you likely to make of this? I’m assuming the buzzer will be hand-soldered?
So, you make the hole big (and save having to create a new footprint!), and need a tiny bit more solder to fill the hole… is that ACTUALLY an issue for you? (as an engineer, I realise perfection is never achievable, so I will accept "close enough!)
When you read a spec, you can end up thinking that all the tolerances can add up, and theoretically, that is 100% correct. The reality is that most devices will be much closer to their nominal values, so you’ll often get away with making those holes a bit smaller. You say the pin is oval… so maybe 0.5 x 0.7 (which is 0.6+/- 0.1)? (a VERY useful tool when you are doing this sort of thing are Digital Callipers, great for measuring pin diameters / spacing!)
In terms of PCB manufacture tolerances, I guess those come down to inaccuracies in the hole plating.
Like Piotr, I have “molex pins” that are square pins (that DO fit into a round hole!!), also have some “flat pins”… components made from sheet metal punched to shape (PCB phono sockets specifically), again using round holes.
It’s highly recommended to use round holes wherever possible. Round holes are easy to drill for the PCB manufacturer, while any other hole type (I.e. routed slots) are more difficult, and maybe not even supported by all PCB manufacturers.
And the solder will just fill up the excess. The most common exception is the “barrel jack” connector, which would need very big round holes if round holes are used.
Yes, it will be hand soldered. I don’t mind making it too big at all, I’d rather have the part fit than not. So therefore I assume I could use 1mm hole size?
However, I still need to create a new footprint. There are no footprints (as far as I could find) for buzzers with RM5.0 (5.0 spacing between the two pins).
…or, wait - after measuring the buzzer that I received again I realize the distance between the pins are NOT 5mm. It seems to be closer to 7.6mm, and there is already a footprint for such buzzer.
Did I interpret the datasheet wrong, or have I received something another part than the website I am ordering from claims?
7.62mm is 3/10 banana unit, an you can try if your buzzer fits on regular matrix board with a pitch of 2.54mm.
Also, if your buzzer is actually 5.0mm or 7.5mm, then that’s most often close enough that it still fits on the “freedom units” grid, but it also depends on the pin diameter, versus hole diameter.
That datasheet is a very Chinese one, so whilst you bought the item locally, it’s undoubtedly from China, so I am not at all surprised that what you got and what the drawing says are different. It will be their “upgraded and improved” model (they couldn’t get the original ones, so sent what they could get hold of!)
I sourced a pack of 50 Micro-USB PCB power sockets: no specs at all, so just waited for them to arrive before creating a custom footprint. Print it out, check it, edit it, repeat.
If you do much hobbyist stuff, I’d really recommend getting some callipers: I managed for years without them, now I don’t know HOW I managed! So quick & easy to measure small components!
