Will the proposed "the 12V" relay act about the same with a 3.3 V closed circuit?

Thread Starter

TheManKinahan

Joined Mar 18, 2008
3
Mods Edit:
Please don't hijack other member's thread, now you have your own.
This thread was split from -- Need help with a Constant to Momentary Relay



Since this thread is a couple years old maybe I can briefly hijack. I haven't done any circuit stuff in quite a few years. I have my keurig on an automatic outlet with a manual switch as well. I was trying to make sure it was heated up and ready to go in the morning, so I cut the power switch and soldered it together. I think it's ~3.3 V circuit. Now I discover its a momentary switch, and the display goes off, and only stays on if I hold a button (such as brew) down.

Will the proposed "the 12V" relay act about the same with a 3.3 V closed circuit? Can I increase the time (to close to 4 seconds, by increasing the capacitor value by 4s/1.5s or 8x (8000 uF)? Lastly, would the relay close with a 5V line from something like a iphone/usb cable? I assume similar to a ssr, the close current is very very minimal?

Thanks......
 

Thread Starter

TheManKinahan

Joined Mar 18, 2008
3
It seems more complicated than I would need. First, I've read the voltage for the LCD, etc is 3.3 V, but I don't know for sure. Is there not a simple analog momentary relay? I looked over the 555 documentation you provided and the wikipedia, which mode would I utilize?
 
This may be a bit more tricky that you want it to be unfortunately.

An interface that usually works is an OPTO-FET. One of the coolest is the vactrol VTL5C1. http://www.excelitas.com/downloads/dts_vtl5c1c2.pdf The cool part is leads. So, if the "switch" will operate with a 200 to 600 ohm resistor, your good to go.

OPTOMOS relays can be used if you need a lower on resistance.

The nice part os you don't have to use a real relay and you don;t have to figure out what your working with. e.g. A scanned matrix of switches.

One think I did one was to make the input handle something like 6 to 30 V.

The one thing your going to have to do is find out what power supplies are available. e.g. 3.3, 5 or 12 V

Unfortunately, delays on power up or what might be called a "delay on make timer" always seems to be problematic. The 555 is disastrous and long time periods > seconds also cause issues.

You will have to test and see if the machine can stomach a closed button held before power up and then released or does it need a certain amount of time to power up and then it has to be pressed for a minimum time and it also has to be released.

I don;t know how this: Timerblox http://www.linear.com/product/LTC6993-1 (multiple versions) behaves on power up.

It might be possible to combine a reset generator (e.g. http://www.st.com/web/en/catalog/sense_power/FM1946/SC665?s_searchtype=keyword) and a timerblox to get the pulse you need.

This http://www.galco.com/buy/SSAC/TS1423 has other issues, but it is a delay on make. 120 VAC does dissapear instantly. You would have to use a real 120 VAC relay. It might not work unless you can hold the button during/before power up and then release it.
 

Thread Starter

TheManKinahan

Joined Mar 18, 2008
3
Now that I've looked into it more, it does seem like the 555 IC is perfect. I think it will be very forgiving with closed times, and it looks like there are versions with a cap, an adjustable timer (pot) and screw terminals already made for 2 bucks. I'll try that and report back.

I looked for a hot 12/5/etc connection, but unfortunately those connections are all at the top of the machine. It was a PITA to take apart last time, so I think I'll just pickup a 120->5 V adapter. and hide it on the bottom.
 
Top