EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: bpiphany on December 11, 2016, 10:09:45 am
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I recently found out about this type of rotary DIP switch (http://www.apem.com/Miniature-DIP-coded-rotary-switches-v9-d-850.html) (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?
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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?
Your thought experiment is: Should that be break before make or make before break? Pullups are the correct solution.
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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 point :-+
Edit: Besides there are regular double throw DIP switches like these these (http://www.digikey.com/product-detail/en/e-switch/KAT1108E/EG4555-ND/666103) And 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 :-DD
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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,
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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?
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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,
That'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 (http://www.digikey.com/product-detail/en/te-connectivity-alcoswitch-switches/53137-5/450-1186-ND/298017).
The BCD datasheet has a more illustrative functional diagram, link (http://www.digikey.com/product-detail/en/te-connectivity-alcoswitch-switches/53919-2/450-1190-ND/293971).
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..
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Edit: Besides there are regular double throw DIP switches like these these (http://www.digikey.com/product-detail/en/e-switch/KAT1108E/EG4555-ND/666103) And 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.
Cute little switch, but its a 3 pole On-Off-On.
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?
If 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 are wasting dissipating 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.
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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.
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little switch, but its a 3 pole On-Off-On.
I may be new and certainly not get my switch nomenclature right every time, but I'm pretty sure that's not correct.
From Littlefuse (http://www.littelfuse.com/technical-resources/technical-centers/commercial-vehicle-technical-center/poles-and-throws.aspx), since they were first in my google results. I'm sure someone else has an other definition...
What do SPST, SPDT, DPST, and DPDT mean?
SP and DP refer to single pole and double pole, ST and DT refer to single throw and double throw.
Pole refers to the number of circuits controlled by the switch: SP switches control only one electrical circuit. DP switches control two independent circuits (and act like two identical switches that are mechanically linked). Do not confuse ‘pole’ with ‘terminal’. The DPST switch, for example, has four terminals, but it is a DP, not a 4P switch.
Throw refers to the extreme position of the actuator: ST switches close a circuit at only one position. The other position of the handle is Off. DT switches close a circuit in the Up position, as well as the Down position (On-On). A DT switch can also have a center position (frequently On-Off-On).
Single pole/throw and double pole/throw switches are by far the most common switches, but triple and quadruple configurations are also available. They are commonly denoted 3PST, 3PDT, 4PDT, etc.
I 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.
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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.
Interesting, it's easy to learn when you know little :-+
So let's say I want to use this lvc163 (http://www.nxp.com/products/discretes-and-logic/logic/lvc/presettable-synchronous-4-bit-binary-counter-synchronous-reset-based-on-pip-74lvc163:74LVC163) counter from NXP
That 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 <5µA
The TI datasheet (http://www.ti.com/product/SN74LV163A) (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?
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little switch, but its a 3 pole On-Off-On.
I may be new and certainly not get my switch nomenclature right every time, but I'm pretty sure that's not correct.
From Littlefuse (http://www.littelfuse.com/technical-resources/technical-centers/commercial-vehicle-technical-center/poles-and-throws.aspx), since they were first in my google results. I'm sure someone else has an other definition...
What do SPST, SPDT, DPST, and DPDT mean?
SP and DP refer to single pole and double pole, ST and DT refer to single throw and double throw.
Pole refers to the number of circuits controlled by the switch: SP switches control only one electrical circuit. DP switches control two independent circuits (and act like two identical switches that are mechanically linked). Do not confuse ‘pole’ with ‘terminal’. The DPST switch, for example, has four terminals, but it is a DP, not a 4P switch.
Throw refers to the extreme position of the actuator: ST switches close a circuit at only one position. The other position of the handle is Off. DT switches close a circuit in the Up position, as well as the Down position (On-On). A DT switch can also have a center position (frequently On-Off-On).
Single pole/throw and double pole/throw switches are by far the most common switches, but triple and quadruple configurations are also available. They are commonly denoted 3PST, 3PDT, 4PDT, etc.
I 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.
Sorry for the confusion you are of course correct, there are 8 On-Off-On switches with common connections to all of their On sides.