using tact switch for power toggle

Design Concepts
1

i originally posted this as a question in another thread, but i thought other people might want to try it so i’m putting it here to make it more obvious what it is.

anyway, i found a good circuit for using a tact switch as a power toggle.  i’ve tried it out and it works fine.  what i’m trying to accomplish next is putting a small time delay when it switches, so you have to hold the power button for a half second or so until the device turns on or off.  someone mentioned using a 555 timer for this but i tried it and wasn’t successful.  does anybody have any ideas how to modify this schematic to make it take longer for the power to come on?

ultra

the description of the circuit can be found here (third one down): http://ourworld.compuserve.com/homepages/Bill_Bowden/page9.htm

2

Interesting circuit, but I don’t like how the load isn’t connected to the same ground.

That makes life harder, or maybe I’m just paranoid, I wouldn’t want an audio ground to be sitting on top of a MOSFET. Not that I’m starting a FUD campaign against the idea, I just don’t know…

This looks like an easier build…

http://www.edn.com/index.asp?layout=article&articleid=CA6421439&spacedesc=designideas&industryid=44217

and appears like you can configure the press time required to toggle the power… I would then drive a MOSFET from the output to supply current to the rest of the circuit rather than sink it. I am intrigued by how simple this one is… I think I might try it out.

3

i’ll give this one a go too.  thanks

4

I’ve made a mashed version of those two schematics, with a little boolean in there too. If someone can give me a hint as to how to host images (on the wiki?) I can post it.

5

thanks!  you can’t post images on the wiki but you can link them.  if you e-mail me i will put it on my web server.

6

Well there are two options for storing it onsite :

a) Attach it to the forum post, and link to that from the wiki

b) email it to “MBWiki” d0t “Upload” 8 “gmail” dawt com and I will upload it to the wiki for you

:slight_smile:

Edit: antispammed that addy. Damn bots.

7

sorry, i forgot to put it in the thread when tilted sent it to me.

8

before i got around to trying to circuit, smashtv linked me to this:

http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1144,P10330

kinda solves the problem i guess :slight_smile:

9

well, i’ve managed to make a power toggling tact switch circuit and it works well.  as i said in the previous post i used the LTC2950 by linear.  you can order up to two free samples of this chip (get LTC2950ITS8-2#TRM).  i mounted the chip on a SOT23/DIP converter board (http://cimarrontechnology.com/index.asp?PageAction=VIEWPROD&ProdID=5) so i can breadboard it.  i think in my final project i’ll leave it on the DIP board and solder that to my pcb.

i’m using .022uF capacitors to set the on/off time, which can be set independently.  the circuit switches on nearly immediately (would take longer with .033uF cap like in the picture on the site), and takes about a second to turn off, so no accidental power-downs :).  i originally tried a .047uF capacitor, but this didn’t work for the power-up all the time.  sometimes, it would turn off again after the approximate hold time for turning on.  i think the capacitor wasn’t charging enough and the chip would cycle power.

anyway, just thought i’d share this so anybody interested in using a tact switch to cycle power can do it.  i do plan on having a master power switch on the back as well, just so i can physically cut power when i want to.