I have not used resistor footprints in KiCad before. If I measure the resistors in my resistor kit, they seem to align with:
“Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal”. I have tested this by measuring their pitch and using a ruler to compare the bounding box around the footprint
and the actual resistor size (do not own a suitable tool for measuring diameters). I have not ordered a PCB with this footprint before. All I can say is I did a silly mistake of using a 2.54 pitch connector footprint back in the day…
I would think that this resistor size is very common. Maybe I have selected the wrong footprint?
Because, after looking at a bunch of datasheets online, it seems like this is not a common resistor size? Most ones either seem to have a pitch of around 2.5mm or 10mm.
Could someone confirm if this is a common resistor size footprint or not? If so, could you point me to a model number or manufacturer? (or, some keywords I should use to find these resistors).
You don’t have to buy THT resistors that exactly match the footprint. You can buy shorter ones (provided the power and voltage specs are adequate) and form the leads to suit, using formers lke these:
The pitch is encoded in the resistor name. P7.62mm is three bananas, and apparently you managed to put your resistors on that grid, but the bends are very tight and close to the ceramic of the resistor. And this risks damaging the resistor (or the epoxy coating). It’s more common to use the 4 bananas P10.16mm sized pitch for the DIN0207 resistor size. (Edit: MF25 seems to be (nearly) identical size to DIN0207. XKCD/927)
Also, sometimes an even bigger pitch is used for this same resistor size. Especially on the old single layer PCB, this gives more opportunities for the routing, ad the resistors are used to jump over other tracks. Longer wires in general also have a better cooling effect. In some precision applications the wires MUST be bent at the same distance from the resistor body to balance out this heatsink size, and this is done to minimize thermocouple effect on the transition from the connecting wire to the resistance element. If the ends of the resistor are at different temperature, (because of asymmetric cooling), then the resistor can develop a few micro volt, and in some applications this is significant.
For me it was common when I was young. During 90s I moved to 1206 then to 0805 and then to 0603. So since about 1997 for me only common are 0603 resistors.
Try using SMD resistors. Soldering them is even simpler than THT resistors (you have everything at one PCB side - no need to continuously revert it).
I use some tiny long-nosed pliers, and by putting then adjacent to the body & bending the wire, I get a nice 0.4" length (and no potential damage to the resistor body). Those bending formers are a good - and cheap - idea too. (ali express: https://vi.aliexpress.com/item/1005009009988657.html). Professionals would probably use a special tool for cutting & cropping axial components
For most “hobbyist work” the MF25’s are fine. The MF12’s are even tinier, I’ve used them a few times where PCB space was tight. If I was looking to go further with my PCBs (I’m retired now, so it’s just for small modules I make) I’d certainly be looking at surface mount resistors and maybe caps too.
If you’re curious about SMT resistors, then do a little search for “Resistor Sample Book 0805” You will find neat little books that have resistors in E24 range, all values ( 1Ohm to 10Meg Ohm or thereabouts) and 25 or 50 resistors for each value. 4250 resistors for around EUR20, and that is about 0.5ct per resistor. “0805” is the size, and it’s a relatively big size and quite easy to handle with tweezers.
And there are similar sample books for other parts such as:
Ceramic capacitors
Inductors
chokes.
LED’s
Transistors / diode assortments (mostly SOT-23)
Good quality tweezers is a must, and a stereo microscope is also very handy, although young people with good eyesight can do without. Having a lot of light on your desk (And I really mean a lot) also helps. With an “excessive” amount of light, your pupils retract, and as a result, you use less area of the lenses in your eyes, and as a result you see sharper. It’s similar to changing the aperture in a photo camera.
Yes, depth of field is of course the obvious, but if you use a smaller portion of the lens, then a bunch of other non-ideal properties of the lens also get reduced. With a pin hole camera you can even get a picture without any lens.
The easiest way to see if you can benefit from more light on your desk / work area is to take your test object outside on a sunny day, and then look at it in the same way.
Direct sunlight is around 1kW of light per square meter. I’m not exactly sure about efficiency of LED lighting. I guess it’s <20%, maybe 10% is probably more likely, but anyway, it would translate to several kW of LED lighting on your desk.
Unless you need to squeeze a minimum size, small axial resistors can be placed into a half inch or 12 mm pitch. Leads can be bent by supporting the lead with a needlenose pliers to prevent stress on the resistor body.
But given that you are using KiCad, that means you are doing pcbs. For pcbs IMO there is no advantage to axial resistors for low power/ low voltage. My hands have “essential tremor” but I place 0603 resistors on a small 0805 footprint routinely and easily using a good tweezer. I am farsighted but I wear “close and closer” bifocal eyeglasses. Together with an LED fluorescent lamp over my bench I am all set.
0603 resistors are now cheaper than axial, and they will save a lot of board space. They are easier to swap than axial resistors (you do not need to use a solder sucker).
I stock 0603 and 1206 resistors in my lab; I do not bother with 0805s except for some values < 1 ohm.
