aiu switches

@bullfroggs posted:

hello. can mth's aiu switches be wired in a way to make them constant on instead of momentary?

Unfortunately, they cannot.

thank you

An AIU has the ability to control 10 turnouts and 10 accessories. Granted, the turnouts are momentary. The accessory relays are maintained.

Not sure if the OP was referring to the AIU relays as "switches" . Or, if he was referring to turnouts. FWIW, if can't think of why you would want to maintain power on a turnout coil.

I think Gilly has the right answer, if you wire as an accessory, they'll stay on until you turn them off.

hello and thanks for the reply. what i mean to say is my aiu accessory ports are all filled and i need another port to run an accessory which i have none. i was hoping there would be some way to wire the switch port to make the accessory that i want as a on or off switch not momentary.

AIU's are pretty cheap.

A reason to have an AIU SW(itch) port latch in the Straight or Diverge position is if driving a Tortoise type switch machine...as opposed to the snap-action solenoid coil switch machine.  The AIU SW ports indeed fire for only 1/2 sec.

For the matter at hand you can add a latching relay external to the AIU.  In fact this is what MTH recommends if using the AIU SW port to drive a Tortoise.  You then press "straight" and the relay latches in one position, You press "diverge" and the relay latches in the other position.  And you need a DC power supply (e.g., 12V DC) to power the external latching relay(s).  It's not that all these external components are expensive but when you add up the hassle it makes purchasing an additional AIU an attractive option!

hello stan. thanks for the reply. ok, sounds good. now, because i am not very good at electrical can you show me the way to wire a latching relay, etc. and list parts i can order to do this and if you can a simple schematic. i know its a lot to ask but i am desperate. lol

For the Accessory ports on the AIU, you can operate them in either constant on or momentary mode. The wiring is the same at the AUI connection. The difference is in the remote.There are 3 settings when you access a particular port under ACC on the remote: OFF, ON, ACT. ACT is the momentary function. The accessory stays active only while you hold the soft key down. Let up, and it shuts off.

Chris

LVHR

Why would you go thru the trouble of getting a latching relay and wiring it up when you can get another AIU?

A NEW AIU is $120 MSRP from MTH and a dealer will discount it. Flea bay or amazon may have them new or used cheaper.

The most I've ever spent for an AIU is $70, and I bought a couple for $50 right here on OGR.

@bullfroggs posted:

hello stan. thanks for the reply. ok, sounds good. now, because i am not very good at electrical can you show me the way to wire a latching relay, etc. and list parts i can order to do this and if you can a simple schematic. i know its a lot to ask but i am desperate. lol

If electrical assembly/wiring/soldering etc. is not in your comfort zone, I'd opt for getting another AIU if they can be had for $50 (that really is a great price!).

But, let's take the application at face-value...if for no other reason than OGR is a discussion forum for the exchange of ideas.  I haven't checked current pricing, but a couple years back I wrote up how to turn an unused SW port into an ACC port for about $5 in external parts.  Lots of wiring but no soldering required.  The write-up is on the O gauge archive site here...videos included!  Here's a photo from the write-up ... convoluted but it works as advertised!

The reason the above is so cheap is because relay modules off eBay are insanely cheap (about $1 per relay) so you can mess with the wiring to use multiple non-latching relays to configure a single "latching" relay.  Let's be clear here.  This is more about having "fun" with the hobby in the spirit of a discussion forum!

The direct method would be to use a genuine latching relay.  You'd use a so-called dual-coil or twin-coil latching relay.  A brief pulse to one coil "sets" the relay, a brief pulse to the other coil "resets" the relay.  The half-second pulse generated by the momentary AIU SW port outputs is the source of the set and reset pulses.  There are several off-the-shelf, no-soldering-required, modules such as from Azatrax:

After shipping and adding the cost of a 12V DC wall-wart, it's in the $20 ball park...with each additional port still being around $15.  Not very competitive to a $50 AIU but no soldering and you do get 8 Amp contacts (more than the AIU's internal ACC port relays) and double-pole switches which have their application in life.

And here's how it would wire in comparing to the el-cheapo configuration.

Finally, one might look at the above off-the-shelf module and rightfully observe that if you don't need the convenience of the screw-terminals, and don't mind soldering, why not just get a bare bones dual-coil latching relay and wire it up.  For example, for about $2 you can get the Kemet EC2-12TNU 12V dual-coil latching relay with 2 Amp contacts.  The net result so to speak is the same.  There are 3 wires from the AIU SW port going into the relay...and 3 wires come from the relay behaving like an AIU ACC port.  I don't know how many Amps you are trying to control with the "new" ACC port but you can get "loose" latching relays with higher Amp ratings.

Or if you converting many ports and don't mind waiting for shipping from eBay-Asia, less than $2 a relay delivered to your front door.

A DC power source such as a 12V DC-output wall-wart is a constant in the above schemes.  But in the latter case, if you don't mind soldering and such and 2 Amps is enough, then you should be able to create a few extra ACC ports from unused SW ports for just a few bucks per channel.  If you are considering this latter method, I can detail the exact wiring to the "spider legs" under the relay!

Again, in the spirit of a discussion forum, I re-read your original question which asks for a way to have an SW port become constant ON (rather than on for only 1/2 sec).  Another alternative is a toggling relay.  This is described in the link I provided but it may be an even more cost-effective solution and doesn't require soldering.

By toggling I mean you trigger it once and the relay turns on.  You trigger it again and the relay turns off.  So in this context, you could press the AIU SW "diverge" button and each press would toggle the relay on and off.  Presumably you're standing right there on your layout being the master-of-the-universe so maybe that's good enough!?

Here's the photo from the linked archive write-up on the toggling relay method.

You still need a 12V DC power source such as from a wall-wart adapter.  As shown, the toggling relay (10 Amp contacts) connects to AIU SW Port #3 between the "IN" and "2" terminals.  So in this case every time you press the "Diverge" button for SW3, the relay toggles and becomes "constant" instead of "momentary."

Again, this may or may not apply to whatever it is you use the ACC ports for!

But if this applies, note that each unused SW port can control two toggling relays.  That is, the "straight" button toggles one bistable relay module.  The "diverge" button toggles another bistable relay module.  So as an extreme example, if you have 10 unused SW ports on an AIU you can make 20 "new" constant-ON/OFF ports!

And when you turn off power to your layout, all the relays revert to their "OFF" position.  So when you power up your layout next time, all the relays are OFF.  That's how the AIU behaves between operating sessions!  That is, if you use a true latching relay, it remembers its ON-OFF setting between operating sessions.  So if you had a latching relay turned ON when you power off your layout, the relay is mechanically latched in the "ON" position.  When you next turn on your layout, whatever gadget is being controlled immediately turns ON.  This may or may not be desirable so is a consideration if using a true latching relay.

hello stan. outstanding reply. just what the railroad fan needed. new aiu is a good answer but it is time to use some of those sw's that are not being used. thanks again.

If you can't tell, I've given some thought to this topic.

Stan, Once again, I benefitted from a learning experience made possible by you, OGR, GRJ, and others.  I had fun figuring out your logic on how you can wire 3 relays to make one latching relay.  I had to pretend I was an electron running around the wires to do so, but it was a path worth traveling!  Haha!