I'm still waiting for my newark order so I went ahead and worked on the 555 solution. Based on the suggestions I got I came up with this. It has a few more components than some of the other solutions but it is working pretty well. A 100uf capacitor is giving me just about exactly 2 minutes of delay before off. I imagine there may be ways to eliminate the front transistor but for me it helped to have each active component doing one task. The transistor on the front deals with my normally closed, open is on, pressure switch. The 555 gives me 2 minutes of delay. And the transistor at the end drives the relay. The release is very clean and consistent. The relay is one of those 12 volt "ice cube" ones and is drawing about 150ma so I suspect I could get rid of the second transistor. The circuit draws about 14ma when "off" and I think I can live with that. I'm still planing to try some of the other suggestions once I get more parts. Thanks to everyone for all the help. I have learned a bit more :-)
- posted
15 years ago