The old Radio Shack catalog had two rotary switches. One was a
12-pole, 1-position, shorting. The other was a 2-pole, 6 position, non-shorting. The second one is the only one left now:
I don't understand the lingo. Can someone point me to schematic symbols for these two switches, or an explanation of what they do? And what is the "shorting" thing all about.
More generally, I'm making an intervalometer for my camera, and in order to change the period between pictures, I need to vary one of the 555 timer resistors. And I thought a multi-position switch of some kind, with individual resistors, might work better than a pot. But I also need an on/off switch for the whole thing. Can the R/S rotary switch be rigged to do both functions?
The "one position," or one pole, switches a single entity between one of twelve other entities (either side could be the input or output). "Shorting" is a "make before break" type, where in the transition between positions there will be a spot where two of the 12-side entities are connected, or "shorted," together and both of them are connected to the main pole.
The two pole, six position switch connects each of the two poles individually to one of six other contacts. "Non-shorting" is "break before make," where in the transition between positions there will be a spot where none of the 6-side entities are connected to the corresponding main pole.
I think you would do better using a pot. Radio shaft used to sell a add on switch that you can put on the pots they sell, you simply remove the cover to the pot and replace it with this switch..
AS far as the shorting term goes, it just signifies that the leaving contact and approaching contact will be joined as you change selection. This will work fine if you are making a R latter, I don't know about other functions how ever..
What the switches do is to sequentially connect and disconnect one moveable contact (the "common") from a series of fixed contacts (the "contacts) as the switch's shaft is rotated.
"Shorting", or "make before break" means that before the switch common leaves one contact it contacts the next, and "Non-Shorting", or "break before make" means that the common leaves one contact before it contacts the next
A "12-pole 1 position" switch is a misnomer, since all switches must have at least two positions.
A 12-pole 2 position switch would be a switch with 12 commons and 12 contacts, where the commons would connect to, or disconnect from, their respective contacts in unison.
A toggle switch equivalent would be a 12-pole single throw (12PST) switch.
A 2-pole 6 position non-shorting switch would be one with 2 commons and 6 contacts per common, where the commons would disconnect from one contact before engaging the next.
Or Google "rotary switch" for more.
>More generally, I'm making an intervalometer for my camera, and in
Ok, on this point, so the R/S switch is really just two single pole switches ganged together. Then that may be the lowest cost and best solution. I'm trying to make this as cheap and easy as possible for others, with everything available at R/S. I actually have the R/S 1meg linear pot, and it's not worth a damn - the first 30 degrees on one side produces no change at all. And, they no longer sell the add-on switch for that pot. So if the rotary switch can do timing plus on/off, then that's going to work best.
Yes, that's what I mean by intervalometer, but I don't see the need for the second timer section. The shutter-press pulse duration will be the discharge period of the first timer section, and that's determined solely by the value of the discharge resistor, which isn't going to change. I've found that I get a bit under two seconds of shutter trigger with a 100ufd cap and a 22k resistor, and that period isn't going to change no matter what I do with the interval between shutters (the charge period). I've breadboarded this, and it does work. Unless I'm missing something.
[As an aside, I found that you can almost completely isolate the charge and discharge times by putting a diode parallel to the discharge resistor forward-biased toward the cap, so that the cap charges through the charge resistor and the diode, but discharges though the discharge resistor. That's how I get a Do you need a circuit description?
No I don't think so.
Well, this is pretty much a short term intervalometer, with an interval between pictures of about 1 minute or less. The
1meg pot is about right for the charge resistor, or the equivalent using the switch. It would be nice to provide for longer intervals, but I just don't know how big a resistor I can use with a bipolar 555 and an electrolytic cap
- leakage and such.
But coming back to the second timer section. I'm also doing a second version where there are actually two shutter pulses, the first being a "half-press" contact, which causes the camera to autofocus, etc., and the second being the actual shutter contact. The first contact needs to stay engaged while the second takes place. So I need the half-press pulse to last for, say, two seconds, and the shutter pulse needs to begin one second into the first pulse. Then both should terminate together.
For that, I use the second timer section purely as a flip-flop. I connect the output of the first section to the trigger and threshhold of the second through a circuit that provides a one-second delay going low, but an immediate response going high - through a diode. Well, I'm in the process of drawing this up, and will post it in the schematics newsgroup.
Thanks again for your help with the switch. Let me know if there's something I haven't considered re needing another timer section for the pulse period.