Ahhhhhhhhh! I am an old geezer who remembers using standard TTL when that was the logic family dejour. LS logic followed it within a few years.
LS logic is bipolar and not CMOS. It requires significant input current. From the TI datasheet (CAREFUL I see that both the LS and non LS on the same DS!!) I see maximum input current of 0.4 mA at 0.4V. That means that a 1K resistor is theoretically the maximum that you can use as a passive pulldown. My takeaway is do not do this with 74LS logic. Perhaps you could use 74HCT logic (CMOS family, much lower input current but generally compatible with 74LS) or redesign with a gate or inverter. Due to asymmetrical input current requirements, passive pullups work much better than passive pulldowns with 74XX and 74LSXX logic.
With a 10K pulldown, at the input of 74LS logic I am not sure what will happen and I guess the hardware agrees.
Thank you, Rene. I had similar question but am not so eager to join those forums.
Those values are for TTL and not LSTTL. But you are on the right track. Passive pulldowns at inputs to TTL and LSTTL are generally not a good idea. There may be some special exceptions.
Gotcha. The only reason I using a pull down resistor to keep the MR line from floating high if the input is floating. But yes, I think I will redesign using HCT series chips.
Would it be unreasonable to add a category for circuit design? Yes of course it is not strictly related to KiCad but it is loosely so; not like we would be discussing movies or pop music.
I think that the forum is probably good for KiCad and vice versa. A slot for circuit design discussions might even draw more designers into KiCad.
But suppose you like to have some tunes coming through the headphones while youāre laying out boards? Sort of like my daughter, who used to do TV while she watched homework . . . . and still had the second-best academic record in her High School class, which aggravated her older brother.
Some people just have it. Sometimes I hear about students who did well in biology but changed to EE and did well in that, then got a PhD in Chemistry while writing books on ancient history. As for me, I can only do one thing well enough to get paid to do itā¦
Actuallyā¦ I have a board moving through fabrication now that Iām planning to assemble over my Christmas break, so this selection would be appropriate.
One of my tasks for this weekend is to submit my parts orders to Mouser and Digi-Key so the packages donāt get delayed too much by the holiday rush.
The forum is not currently setup to nicely separate different categories. I am not even sure the software is able to be used like the older forums with different sections. Discord is meant to be used by single topic communities. (It is used quite a lot by communities around games)
So while it is not bad if we get such questions from time to time i do not think it would be wise if these questions would take over. After all this forum has one purpose: To help users with KiCad.
You always have to draw the line somewhere. There are already some pretty good forums for general circuit design up and running. Let the folks making money from it worry about the headaches of being a constant target because of the large user base.
Years ago I did hotline support for C compilers what pushed me soon unintentional into several projects not only from beginners and companies with low personal resources. Users claim the compiler works wrong. Typical support job is to explain why to use the volatile keyword and why it cannot work without. āProfessionalā programmers asked: Why do we need to have a stack? Examining an aircrafts multi-controller code my hairs stood on end when I had to explain the customer why his code is unusable for safety reasons.
This way, there seems only a weak line between tool and design support. Why not using the forum project section? It would be interesting how far @Seth_h covers this with the commercial contracts.
Thanks, Rene. It is not my intent to drive this idea too hard, but I wanted to be sure we avoid one possible misunderstanding. I figure we already have a bunch of categories: Community, schematic, software, layout, etc. so this would only be one more.
I donāt know where you live, but in Puget Sound WA the issue of āPorch Piratesā stealing packages from peopleās front door gets a lot of attention in the news media. Especially now around the holidays. Those crooks will see only that it is a package and never heard of Mouser or DigiKey which is printed on the outside of the box. What do you think those !@#$%^&!! will do with $200 worth of electronic parts once they get it home?
For me, the last three on your list are irrelevant and I checked out the first. I see people writing articles (or blogs?), but I do not see people asking questions. Am I missing that somehow?
Thanks, iitgrad. Yes I have come up with Stackexchange a number of times over the years and it does seem worthwhile. Part of what I was thinking is that I like this KiCad info forum community. It seems that good circuit design questions seem to belong, at least up to a point. I have not spent a lot of time at Stackexchange, but the conversations at Kicad info forum seem so much better than whatever else is on the web, 99% of the time. I am in a position to help others in some areas, but sometimes get stuck on software or perhaps some details on getting boards made.
May be it will be interested for someone.
Many years ago I asked some questions at Usenet group: sci.electronics.design
As Usenet server I was using was switched off (Usenet is dying ) I am using now Usenet server set-up by private person and he subscribes only local groups.
Some people just have it. Sometimes I hear about students who did well in biology but changed to EE and did well in that, then got a PhD in Chemistry while writing books on ancient history. As for me, I can only do one thing well enough to get paid to do itā¦
) I am using now Usenet server set-up by private person and he subscribes only local groups.