I need some time delay pushbutton switches on my layout. I find sutable switches on ebay for cheap ($3.75) from Hong Kong. I see same switches on sites like Amazon for $22 and more. My concern is how reliable they might be. I saw reviews on similar switches saying they were DOA or failed soon after installation. Anyone here used similar switches? How long did they last?
If these Hong Kong switches are doomed to failure, can anyone suggest a switch that would be more reliable?
This sounds like a good application for using Arduino. You may have to do some experimenting to get your final results but for time delay you would be able to customize it for your particular application.
Google “arduino timer pushbutton” and go from there.
Good Luck, Ed
You can build one for yourself on the cheap if you have resistors, capacitors, and a transistor or two. Parts are commonly available on amazon. <<$10.00 and no programming necessary.
https://www.eleccircuit.com/off-on-after-delay-switch-by-mosfet/
https://www.homemade-circuits.com/simple-delay-timer-circuits-explained/
The secret is in the capacitor. The larger the cap, the longer it takes for the current to pass through the transistor. You can also use a zener diode on the base leg of the transistor to go from a more traditional pure on/off state.
A little bit more consistent one can be made with a 555 timer IC - dime a dozen. See Rob Paisley’s circuits page http://circuitous.ca/LM555.html#4
Circuit 5 is of the type “push the button, it turns on for a set tiem then shuts off” circuit. Dependong on what you are powering, you may be able to hook it right to the 555. Or you could have the 555 trigger a relay to drive a larger load.
–Randy
Oh good call. Totally forgot about that little gem of an IC.
Thanks but I am not interested in building my own. Too many other higher priority items for my time. After looking at the timers I saw, I realized that they will not work anyway. I want a timer where I can press a button and turn current on to my load for a few seconds then when the time is complete, the circuit turns off and the timer will reset so I can do it again later without me needing to reset the time circuit. Everything I have found so far will initiate the circuit for a set period of time but will not reset the timer unless the power is removed from the circuit.
The 555 ones most definitely does not need power cycled. Push button, circuit turns on for set number of seconds, then turns off. Press button again, repeat the process. Hold the button - it still turns off after the time expires, then you have to release and press the button to start another cycle. Perhaps you can find someone to put a couple together for you? Component cost is minimal.
There is a commercial pre-built version. The Circuitron TD-1. Push button, relay turns on for a period of up to 1 minute, then turns off. Push button again to repeat. No need to cycle power. A bit salty at $34.95 list though. Buying name brand components, no who knows what Chinese stuff from eBay the circuit used about $5 worth of parts.
–Randy
I think this is what you looking for:
https://www.ebay.com/itm/NE555-DC-12V-Delay-Relay-shield-Timer-Switch-Adjustable-Module-0-To-10-Second-/182058770538
Moe
That appears to be another one of those where you have to remove power to start a new cycle, and power has to be applied continuously for the cycle to complete. Based on the description, it’s the sort of thing you would use where you turn on circuit A, and then after a specified delay, circuit B turns on.
–Randy
Here is the one I was looking at but I cannot tell for sure if it needs to cycle the power to restart the timer. I suspect it does thus would not work like I want. It is cheap but would probably need to buy some extrax to cover the ones that fail.
From the description it appears that would be one that would work as desired. Press button, relay clicks, closing one set of contacts, then after a set delay the relay clicks off and opens the contacts.
–Randy
Correct but it appears that the power is supplied all the time and may not have a power break to reset the timer. The price is cheap enough so I am going ahead and order several and see what they do.
Yes, power is applied to the timer circuit all the time. You don’t interrupt it as part of the cycle at all. The power for the item you want to operate has to be run through the relay terminals, where the relay contacts repalce either a toggle switch which would turn the device on continuously, or a pushbutton that would have turned it on only as long as you held the button. Power for the timer circuit and power for the thing being controlled with a time delay are two different things here.
–Randy
Bingo. Bought one of the boards I mentioned earlier and it worked just as I wanted. Power applied to board at all time, push the button and it would power a 12VDC device the selected time then turn device off and reset the timer. You can then repeat the cycle as often as desired without powering down the board to reset the timer.
In my case, I plan to use the board to control the power to some Kadee Electromagnetic Uncouplers. This board will allow me to push a buttion and keep the electromagnet active for 10 seconds thus freeing up my hands to work the throttle to position the cars for uncoupling and pulling away. If I leave the disconnected cars in position, I can then hit the button again and hold the coupler open so I can back up and push the cars into position.
No instruction with board but they can be found on web. Board can handle a load of 12VDC/10A which is more than enough to power the Kadee uncoupler.
This is important to me because I find it difficult to uncouple N scale by hand at my age due to slight hand tremors.
Are you using AC or DC power through the relay contacts to the Kadee electromagnet? If DC, you want to put a hefty diode backwards across the relay contacts because the back-emf from that coil when the contacts open wiill quickly fry the relay contacts with the arcing it will create. The initial surge can be many times the actual voltage applied to the electromagnet coil.
–Randy
Thanks. I am using DC. In my testing, I just used a LED to verify operations. When you refer to a “hefty diode”, what size are you suggesting? Also, what do you mean by “backwards”?
Well, if you connect the power supply - right to the Kadee electromagnet, and connect the + to the relay contact, and the other relay contact to the electromagnet, you would connect the - of the diode to the contact that has the + from the power supply. That’s what I mean by backwards - if you connected the diode forwards, the electromagnet would always be on as the diode would allow current flow around the contacts.
Something liek this (unfortunately small component liek this usully come in multi packs, I found one that was just one diode but it cost almost as much as this 10 pack!)
–Randy
Thanks Randy. I usually understand pictures best but your discription worked for me. Just what I needed. That info will keep me from frying my relays.
After your post about needing a diode, I did some quick research on why a diode is needed. I am an engineer but electronics was my weakest subject in college. I found a good tutorial on the subject and now understand why the diode is needed but I would never be able to explain the electronics behind it to another person. Something about allowing the current from an energised relay to safely escape (vs causing damage to the relay) when you turn the circuit off.
Right, except in this case the ‘relay’ is the coil of the Kadee electromagnet.
If you look carefully at the circuit you bought, there should be a diode across the relay coil which protects the transistor that switches it (depending on the relay used, it might be driven right from the 555 timer chip - but it still should have a protection diode).
Nothing is included across the relay contacts because depending on what you control, it might not need any protection. For example, your testing with using it to turn an LED on and off. There’s no BEMF to speak of and the relay contacts will wear out from physical wear long before any damage could occur from arcing of any sort. But drive an inductive load like the electromagnet and you get that kickback every time the relay is turned off. It’s cause by the magnetic field collapsing across the wires, which momentarily makes the coil into a generator. Without the diode, this causes an arc across the relay conacts as they open. With the diode, the current generated flows through the diode and causes no harm.
–Randy
DC switched under load is prone to more arcing, too. If you look at ratings of switches and relays the current ratings are lower for DC “approved” devices. Some will even say AC only.
https://www.mouser.com/blog/which-switch-who-cares-if-its-ac-or-dc
Having spares on hand is good insurance.
Regards, Ed