Any double throw Rotary switch? - Page 1
Forum section: electronics / projects

author: bpiphany
author_rank: Regular Contributor
timestamp: December 11, 2016, 10:09:45 am
content: I recently found out about this type ofrotary DIP switch(Image attach in case the link breaks). Thought they were kind of cute.They come in decimal, octal, hex, real or complement coded. I can't seem to find one with dual differential "common" pins. Wouldn't it be useful to have both logic one and zero levels in the same switch? No pull up/down resistors. Does anyone know if there is a switch like this out there?

author: Someone
author_rank: Super Contributor
timestamp: December 11, 2016, 10:17:43 am
content: Quote from: bpiphany on December 11, 2016, 10:09:45 amYour thought experiment is: Should that be break before make or make before break? Pullups are the correct solution.

author: bpiphany
author_rank: Regular Contributor
timestamp: December 11, 2016, 10:26:15 am
content: Break before make would be preferable, yes. And yes (now) I see how that would leave the logic level floating while switching. I still don't think that would be completely useless. There has to be some sort of transitional state... But, yeah, I see the pointEdit: Besides there are regular double throw DIP switches like thesetheseAnd DIP switch are usually more for setting values more or less once and for all, no? An intermediate undefined state is not too big a deal.Edit 2: And pullups draw power, very little, but still. On average half of them are going to do it constantly for the lifespan of the thing.Edit 3: I knew I should have posted this in the beginners forum

author: Rerouter
author_rank: Super Contributor
timestamp: December 11, 2016, 10:54:09 am
content: You where already planning on hard connecting the other contacts to supply, would that not pull more power than a pullup to begin with?Outside of that, you could probably cheat, if you used 2 SMD ones, had a hole in the board with one mounted either side of it, and cooked up some small coupler that sat between the 2. though i doubt that could work for large volume, as it would involve an extra step between automated assembly of each side,

author: bpiphany
author_rank: Regular Contributor
timestamp: December 11, 2016, 11:02:04 am
content: If I have say a pre-settable 163 counter, and want to be able to configure it's pre-set value. Then I would tie the inputs to either logic level, no need for any resistors. The input pins should draw minuscule amounts of current. If I instead have pull-up resistors on all four inputs I would expect half of them to be pulled down to GND on average. The whole contraption would then draw 2×(VCC-GND)/R_pull on average, no?

author: bpiphany
author_rank: Regular Contributor
timestamp: December 11, 2016, 11:58:50 am
content: Quote from: Rerouter on December 11, 2016, 10:54:09 amThat's an interesting idea. The reverse one would even turn to the complement which works out nicely. But, even if the individual switches are break before make (which they seem to specify) it would be far from certain they would be synced together well enough to not short out.Now I see that I actually already browsed past a switch that does what I asked for,link.The BCD datasheet has a more illustrative functional diagram,link.I just overlooked that connecting it "backwards" with 4 common+ and 4 common- terminals would achieve what I am looking for. At that price and size it's not happening anyway..

author: Someone
author_rank: Super Contributor
timestamp: December 12, 2016, 12:39:01 am
content: Quote from: bpiphany on December 11, 2016, 10:26:15 amCute little switch, but its a 3 pole On-Off-On.Quote from: bpiphany on December 11, 2016, 11:02:04 amIf the input uses such a small current, then you can size your pull-up/down resistors accordingly. Yes it will use more power than your ideal switch but for typical cmos inputs 100k resistors arewastingdissipating 100uW each, next step would be to only enable the pull of the switches momentarily and read their value before going into a sleep state letting the pull-up/down dissipate nothing.

author: SeanB
author_rank: Super Contributor
timestamp: December 12, 2016, 04:14:20 am
content: With true TTL inputs you do not need pull up resistors, just the switch to ground the input. The input stage of TTL will drift high for any open circuit input. Was often done, and for short traces and a switch that was not operated often it does work well. If you had to do it the other way with pull down resistors you could only use 330R maximum, otherwise the low level was too high for some gates.

author: bpiphany
author_rank: Regular Contributor
timestamp: December 12, 2016, 09:05:35 am
content: Quote from: Someone on December 12, 2016, 12:39:01 amI may be new and certainly not get my switch nomenclature right every time, but I'm pretty sure that's not correct.FromLittlefuse, since they were first in my google results. I'm sure someone else has an other definition...QuoteI would accept the one I linked to be called triple throw if I had to, though one being a non-throw, and I agree the on-off-on nomenclature is more exhaustive. The switch above would be 8PDT, or rather 8×SPDT, or somewhere inbetween since the switches aren't completely independent.

author: bpiphany
author_rank: Regular Contributor
timestamp: December 12, 2016, 09:40:50 am
content: Quote from: SeanB on December 12, 2016, 04:14:20 amInteresting, it's easy to learn when you know littleSo let's say I want to use thislvc163counter from NXPThat would be CMOS and I still need to tie my inputs properly, right? How do I decipher the data sheet?Icc = supply current <10µA. What are those 500µA ?Icc? Is there a way to estimate the average consumption?Il = Input leakage current <5µATheTI datasheet(LV), doesn't explain the abbreviations very much, says only <1µA leakage current. The Icc is higher at <20µA, but there is no mention of the ?Icc.Running at Vcc = 2.5V and 100k? pull-ups, they would draw 25µA each when grounded, which seems very high compared to the input leakage current, and even comparable to the supply current, from what I understand. It seems excessive that the pull-ups would use power on par with the chip itself. Have I got this completely backwards?

author: Someone
author_rank: Super Contributor
timestamp: December 12, 2016, 09:52:45 am
content: Quote from: bpiphany on December 12, 2016, 09:05:35 amSorry for the confusion you are of course correct, there are 8 On-Off-On switches with common connections to all of their On sides.