40 mA is the absolute maximum rating for an IO pin; it’s not a current limited source so if you ask for more the chip will try to give it to you (*), and may destroy itself in the process. It’s up to you to limit the current you source or sink through all IO pins (absolute max is 40 mA per pin, 200 mA total on all IO pins). If you don’t, at some point you’ll fry the Arduino instead of the LEDs
And resistors tend to be cheaper than Arduinos, so you might as well wire things up properly.
*) the output voltage will drop as you pull more current from an IO pin, due to the internal impedance, but the graph only goes to 20 mA. Assuming we can extrapolate, you’d be at 50-120 mA depending on what LED you’re using, which is outside the spec.
mmm I see. I’ll try to add the resistors but the LEDs where already not very bright! In any case, the device needs to work for about 2 hours and then I’ll take the Arduino away, coz I don’t need it anymore
You need both resistors, one to limit the current from base to emitter (and from the IO pin), one to limit the current through the LED (and transistor, but a small transistor can usually manage more current than a small LED). You can tweak the latter until things are bright enough.
Working on an adaptation of this circuit, bit confused about that decay pot there. As you can see the standard “US” pot symbol is used otherwise. I see that the symbol is used for a preset/trimmer pot but that wouldn’t make much sense. Is this just a pot with two leads connected?
It’s the symbol for a “variable resistor,” which (for low power requirements (*)) is realized as a potentiometer with one lead connected to the wiper and the other to one of the ends. It’s common to connect the wiper to the other end while you’re at it:
Thank you @fredrik that makes sense. And @Dud good eye sir yes it’s the bd++. I really liked the sound of yours and the full control set it has compared to other bass drums. I’m probably going to do a kosmo pcb version.
when we have already made a schematic, after having looked at it about 100 times in long and wide to verify everything several times during the build, it is inevitably recorded somewhere in the brain
I was looking at the North Coast Complex VCO circuit this morning and some (not all) of the pots are shown with four terminals:
From context my guess is this means the metal case of the pot is to be connected to ground, but that’s just a guess.
Your guess sounds perfectly reasonable. On the other hand electronics is a field where lots of stuff is standardized, so this symbol should be too.
Maybe you can find this in NEN 5152:2016 or IEC 60617 ‘Graphical symbols for diagrams’
The comments there says “dummy” but potentiometers with a center tap is a thing; search for “loudness” on this page for some discussion: https://sound-au.com/pots.htm
The 4th lug crops up a lot in guitar electronics and usually means the case of the pot and a direct link to the bridge and strings on most electrics or case if it’s metal or heavily shielded. The earth is assumed to be the shielding on the output. If you get a hum that stops when you touch the strings then you need to ground more.
I have a question about the IC bypass cap. Put the cap after or before the wire for +12/-12. Please do you know if one solution is better (why?) or it doesn’t matter at all ?
thx
