thunderaxe
Active member
over spec by how much? and how stable would that make them?
Getting Started with PCBA at JLCPCB
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z2amiller
Active member
I think it matters less for AC (signal), but for DC there's a pretty strong de-rating curve - the capacitance gets less as the voltage gets higher.
The package size is actually relevant here as well, with physically larger capacitors losing less capacitance with a DC offset.
I use X7R 1206 50V 1uF's (basic: C1848) when I do use 1uF ceramics in the audio path.
Murata has an online tool called 'SimSurfing' where you can look up the exact capacitance derating curve for any of their caps.
For example, that 1uF 50V 1206 capacitor is only 500nF when it's at ~40V DC bias. I imagine that the derating curve is probably
at least similar for other manufacturers with the same dielectric/size/voltage rating.
Since the caps in the audio path would usually be biased at 1/2VCC (4.5V or 9V if you're running 18V) I don't think it matters
much for this cap though -- it is stable at ~1uf until ~11V.
But if you were to try to use an 0603 1uF 25V capacitor there, it would be ~750nF at 4.5V and ~500nF at 9V!
(Sorry I'm on my work computer at the moment so I can't upload the screenshots but #trust)
X7R's are also pretty stable temperature-wise, ±15% over their whole temperature range, which is like -55C -> 85 or 125C.
I imagine at the human-tolerable temperatures in that range the difference will be pretty negligible though maybe
if your pedal consumes a ton of power and heats up to 45C or something it could drift by a measurable percent.
(but audio-perceptible? eh)
The package size is actually relevant here as well, with physically larger capacitors losing less capacitance with a DC offset.
I use X7R 1206 50V 1uF's (basic: C1848) when I do use 1uF ceramics in the audio path.
Murata has an online tool called 'SimSurfing' where you can look up the exact capacitance derating curve for any of their caps.
For example, that 1uF 50V 1206 capacitor is only 500nF when it's at ~40V DC bias. I imagine that the derating curve is probably
at least similar for other manufacturers with the same dielectric/size/voltage rating.
Since the caps in the audio path would usually be biased at 1/2VCC (4.5V or 9V if you're running 18V) I don't think it matters
much for this cap though -- it is stable at ~1uf until ~11V.
But if you were to try to use an 0603 1uF 25V capacitor there, it would be ~750nF at 4.5V and ~500nF at 9V!
(Sorry I'm on my work computer at the moment so I can't upload the screenshots but #trust)
X7R's are also pretty stable temperature-wise, ±15% over their whole temperature range, which is like -55C -> 85 or 125C.
I imagine at the human-tolerable temperatures in that range the difference will be pretty negligible though maybe
if your pedal consumes a ton of power and heats up to 45C or something it could drift by a measurable percent.
(but audio-perceptible? eh)
Rpschultz13
Well-known member
I asked this over on AllAboutCircuits. Great thread, especially the Cyril Bateman articles. Also the TI article in post #2 is fantastic.
thunderaxe
Active member
i've got another question: how can i be certain i have the right footprint for the PCBA part? i wish that was a feature of the bouni JLCPCB plugin.
for instance, for a reverse-polarity protection diode, there are no 1n5817s available in basic, but there is this 1n5819 which as far as i can tell is essentially the same thing:
jlcpcb.com
okay, so it's a SOD-323 package, and i take a glance at the easyEDA footprint. should be enough to go on, right? except that there are three different SOD-323 footprints in KiCad, and none of them look like the easyEDA one. the hand-soldered one looks close, but it's not quite right either. worse still, the recommended footprint on the datasheet is different from both the easyEDA footprint and any of the ones in KiCad. i ended up creating my own, but i don't want to have to do that too much. i just want to be certain that i have the right one to make sure the assembly is done correctly.
for instance, for a reverse-polarity protection diode, there are no 1n5817s available in basic, but there is this 1n5819 which as far as i can tell is essentially the same thing:
1N5819WS | Guangdong Hottech | Schottky Diodes | JLCPCB
1N5819WS from Guangdong Hottech - Schottky Diodes is available for JLCPCB assembly, check the stock, pricing and datasheet, and let JLCPCB helps you assemble the part 1N5819WS for free.
okay, so it's a SOD-323 package, and i take a glance at the easyEDA footprint. should be enough to go on, right? except that there are three different SOD-323 footprints in KiCad, and none of them look like the easyEDA one. the hand-soldered one looks close, but it's not quite right either. worse still, the recommended footprint on the datasheet is different from both the easyEDA footprint and any of the ones in KiCad. i ended up creating my own, but i don't want to have to do that too much. i just want to be certain that i have the right one to make sure the assembly is done correctly.
vigilante398
Authorized Vendor
Your SMD footprint doesn't have to 100% line up with the one on EasyEDA, the part just has to fit, oversizing so you have a hand-soldering option isn't a problem. I usually make my own footprints for things, but Mouser and DigiKey have an ever-growing number of footprints for every software out there, and they even offer 3D models. I've never used KiCAD so I don't know what the process for loading a footprint in from a file looks like, but their footprints are pretty reliable.i've got another question: how can i be certain i have the right footprint for the PCBA part? i wish that was a feature of the bouni JLCPCB plugin.
for instance, for a reverse-polarity protection diode, there are no 1n5817s available in basic, but there is this 1n5819 which as far as i can tell is essentially the same thing:
1N5819WS | Guangdong Hottech | Schottky Diodes | JLCPCB
1N5819WS from Guangdong Hottech - Schottky Diodes is available for JLCPCB assembly, check the stock, pricing and datasheet, and let JLCPCB helps you assemble the part 1N5819WS for free.
okay, so it's a SOD-323 package, and i take a glance at the easyEDA footprint. should be enough to go on, right? except that there are three different SOD-323 footprints in KiCad, and none of them look like the easyEDA one. the hand-soldered one looks close, but it's not quite right either. worse still, the recommended footprint on the datasheet is different from both the easyEDA footprint and any of the ones in KiCad. i ended up creating my own, but i don't want to have to do that too much. i just want to be certain that i have the right one to make sure the assembly is done correctly.
If you're making your own footprint (which was the only option in the early days) you typically rely on the datasheet from the part which will give you a recommended footprint. I would usually try to find a 3D model from GrabCAD to drop onto the footprint to make sure the part would land the way I expected.
As a final check, during checkout at JLC they have a visualizer where they'll drop their 3D models onto a rendering of your board, and that makes it pretty easy to see what will fit and what won't. If you order something that won't fit, they'll email you and tell you, and you can either cancel the order and try again or select a different component that may fit better.
EDIT: also if you're looking for an SMD version of 1N5817, try B5817.
thunderaxe
Active member
would this apply to any manufacturer's capacitor of the same specs and package? or just murata's?
z2amiller
Active member
My guess is that the curves won't be exact from manufacturer to manufacturer -- but Murata's numbers will probably be a reasonable
approximation -- under the assumption that this is basically physics, and not some secret sauce in the dielectric material.
thunderaxe
Active member
i'd like to know more about your approach to using JST connectors. it's also what i'd like to do, but i'm worried that stacking the boards directly with pin-to-socket connectors might put too much mechanical strain on the boards and i'd rather have them connected by a ribbon cable, but without having to solder the ribbon cable. i could do pins on both boards and a ribbon cable with sockets on both ends, or i could get a ribbon cable soldered directly to one of the boards and have pins on the other board. that's how my dano mini french toast does it. but i'm not sure how to find the appropriate cable -- the JLC parts library is pretty overwhelming.
z2amiller
Active member
I go into this a little bit deeper in my other pinned thread (https://forum.pedalpcb.com/threads/pitfalls-and-tips-designing-effects-pcbs.28072/), but tl;dr you can buy the cables from AliExpress/etc pre-made - that post has links to the cables I buy. I get the cables pre-made in 100mm (I/O board to footswitch board) and 50mm (footswitch board to effects board) sizes. Agreed that you want to have a ribbon cable in between - they make board-to-board connectors but I haven't used those so wouldn't have a good recommendation.
For the JLC side, you can order the connectors already soldered. The part number magic prefix is:
<orientation><pins>B-<connector type>
where
orientation B = upright and S = 90 degreee
and
connector type PH = 2mm pitch, XH = 2.5mm pitch. (So XH will fit standard 0.1 pin spacing - so you can substitute plan pin headers if you want)
so putting that together,
S4B-XH-(extra stuff) = XH connector, 4 pins, right angle
B3B-PH-(extra stuff) = PH connector, 3 pins, upright
The (extra stuff) encodes some other stuff, like color, how long the part is, and whether or not the pins are slightly crimped to make them easier to solder, but I mostly don't care. I generally buy the cheapest ones that are knock-off JST, they're like $0.03 USD/ea in qty 100.
You can also make your own cables of course -- you crimp them and not solder them, but the whole point is to save time IMO so crimping is for suckers. You can also buy pre-crimped blanks that snap into the housings (like these) so you can make cables that have the color coding you want, but I could never find them in 50mm size so I just gave up on color coding the wires. And yeah, you can solder one end but soldering wires to things also sucks.
What works best for me is right angle connectors on the IO board (audio jacks, DC) that go 4-pins (straight through cable) to a right angle connector on the footswitch board (IN, 9V, GND, OUT), and then from the footswitch board I have 2 3-pin right angle connectors (IN, 9V, misc), (SW, GND, OUT) that go to 2 3-pin upright headers on the PCB (crossover cable). "misc" I can use for 18V or something if I put a charge pump on the footswitch board, or sometimes I use it for a LFO heartbeat signal.
For the JLC side, you can order the connectors already soldered. The part number magic prefix is:
<orientation><pins>B-<connector type>
where
orientation B = upright and S = 90 degreee
and
connector type PH = 2mm pitch, XH = 2.5mm pitch. (So XH will fit standard 0.1 pin spacing - so you can substitute plan pin headers if you want)
so putting that together,
S4B-XH-(extra stuff) = XH connector, 4 pins, right angle
B3B-PH-(extra stuff) = PH connector, 3 pins, upright
The (extra stuff) encodes some other stuff, like color, how long the part is, and whether or not the pins are slightly crimped to make them easier to solder, but I mostly don't care. I generally buy the cheapest ones that are knock-off JST, they're like $0.03 USD/ea in qty 100.
You can also make your own cables of course -- you crimp them and not solder them, but the whole point is to save time IMO so crimping is for suckers. You can also buy pre-crimped blanks that snap into the housings (like these) so you can make cables that have the color coding you want, but I could never find them in 50mm size so I just gave up on color coding the wires. And yeah, you can solder one end but soldering wires to things also sucks.
What works best for me is right angle connectors on the IO board (audio jacks, DC) that go 4-pins (straight through cable) to a right angle connector on the footswitch board (IN, 9V, GND, OUT), and then from the footswitch board I have 2 3-pin right angle connectors (IN, 9V, misc), (SW, GND, OUT) that go to 2 3-pin upright headers on the PCB (crossover cable). "misc" I can use for 18V or something if I put a charge pump on the footswitch board, or sometimes I use it for a LFO heartbeat signal.