Newbee. Sorry. I need to figure out how to draw a DPDT momentary toggle switch on-off-on. This is for a Kato turnout assembly with LEDs .
Thanks
Do you have a link to the data sheet?
No but I will look for one. Also this needs to be a reversing switch.
Can you be a bit clearer about what your question is?
KiCad has a few DPDT switch symbols, and itâs also easy to use the symbol editor to draw your own symbols.
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I think OP is letting this get in the way. A little text can describe the action while using an existing symbol. Or rework the DPDT to show âoffâ as the default.
Modify /Switch/SW_DP3T to indicate momentary action.
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Hi all
Thank you for the suggestions. Unfortunately, I am old school and havenât a clue of as to what youâre talking about. I took electronics in high school but that was 1971. We didnât have microprocessors, chips, CAD, even transistors had just come out. I got some catching up to do. Hereâs a pic of what Iâm trying to do.
The center points on the switch control the turnout and the LEDs on the latching relay. The switch needs to be momentary so as not to blow up the coils on the turnout. The relay keeps the LEDs on till you flick the sw the other way. Simple, yes? Iâve made a few on this style of board and a couple even work! (sometimes)
Now if one you KiCAD guruâs would like to turn this into a schematic Iâm sure you could do it 2 minutes and not even break a sweat. While your at it maybe run it thru the PCB checker and make a gerber. I think thatâs what the PCB makers want.
So, I would be eternally grateful and never say nuthin bad about you!
Thanks, Tim
Just use a standard DPDT switch symbol, and put a comment on the schematic that itâs momentary-action.
I donât think there is any standard symbol for such a switch.
I suppose a Momentary Contact DPDT switch would look like SW2 (see below). This is a modified (by me) Kicad library SW1 with properties changed from âPushâ to âMomentaryâ.
The circuit around SW2 solves the Turnout coil control.
Unfortunately, the other half of the SW will not solve the problem of the latching relay controlling the LEDs.
The best it can do is to latch the relay. This switch will not UN-latch the relay to allow the other LED to operate.
I canât think of an easy solution to @tim1 's problem within his expertise, and besides, this problem is really outside the realms of Kicad usage.
It is probably time to close this thread.
You are a youngster! I went off to college in 1969. When I started EE they had just decided to stop teaching vacuum tubes. (âvalvesâ for some other countries.)
But I do not see that the comments above your post get into much beyond electromechanical switches.
From your description, it seems you have never designed a PCB before. Creating a PCB in KiCad is a bit of an involved process. Itâs not very difficult, but there are a lot of details which all have to be just right.
It looks like you do not want a DPDT switch, but a three position switch with a spring return to the center postion, and momentary actuation of the switches. (Not native english here, I donât know the exact technical terminology).
For PCB design, one of the details to get right is for connecting wires. Wires can be connected by a connector, screw terminals, or soldered, but soldered wires need an additional method for stress relief. Also for the contact outputs of the relay. Where are those going to? What sort of LEDâs are you using? Do these have built in series resistors?
The basic schematic is indeed simple, can be done in two minutes, but the problem is in deciding what you want to make exactly. Connectors are real schematic symbols, and also have real PCB footprints, and there are many different connector types.
And whatâs with the +12V and -12V It looks like you are using a 12V relay, and then put the coils in âantiâ series. This works, but the normal way to operate this type of relay is to only operate one of the coils at a time. One coil for turning it on, and the other for turning it off. This also simplifies your switch and the wiring to it.
This comment from Paul I found interesting.
I spent many years in the telephone industry during the changeover from relay technology (1950s designs using millions of relays with multiple contacts in multi story buildings) to microprocessor technology (1980s and 1990s using a rack of PCBs controlling interface boards).
A latching relay, in my world, had two coils; one with fewer turns and low resistance to activate the relay and one with higher turns and high resistance to hold the relay closed. Power was needed to close the relay and considerably less to hold closed the relay.
What is now called a latching relay (after researching Paulâs comment above) was, in the telephone industry I worked for in the 1980s & 90s called an impulse switch.
Anyway, after this ramble, here is a modified drawing @tim1 can use to wire both his turnout and relay to his switch:
In the industrial switchgear business, there are âMechanically heldâ contactors. They have an On and an Off coil, and the relay is latched, well, mechanically.
That is what these relays appear to be, and that is what was called âimpulse switchesâ in my telephone days.
These impulse switches were used extensively in the very early automatic telephone exchange era (1930s to 1950s).
That works, but Iâd be tempted to wire the two relay coils directly across the two turnout coils. Theyâre wired exactly the same here, even if they donât necessarily look like it. Each switch contact then controls two coils, and you have a better chance of detecting a wiring failure in the circuit that really matters.
If you really want to detect failures though, then youâd rig up a switch that depends on the actual position of the turnout, and use that to run the LEDsâŚ
Regardless though, I always put a cheap âjellybeanâ diode across DC coils, just as a matter of course. It doesnât look like it does anything to the inexperienced, because it appears to be either reverse-biased or off with no other possibility, but it makes the switch (mechanical or otherwise) that controls it last a lot longer.
With just a bare coil, suddenly turning off creates an amazingly high voltage spike thatâs really hard on things, because the current canât stop instantly. A normally reverse-biased diode provides a place for that current to freewheel while the energy is safely dissipated. It also extends the time that the relay stays energized, by a few tens of milliseconds or so, but you probably wonât notice that.
I think you missed that this is a KiCAD forum. Just sayinâ.