Converting a cheap no timer remote to a usable remote

Modifing a $70 fogger to have timed fog.

Yes, you too can spend too much to do the same thing :)

I bought one of the Spencer's foggers (well, 2 of them actually), at the remarkable price of about $70. The only minus to the beast is that they don't support a timer in the remote. When I opened the hand pendant to see how it was wired (doesn't everyone?) I kept staring at the thing,thinking to myself, "There's a lot of room in here...". The more I thought about it the more I realized I could hack a relay circuit in there in parallel with the switch.

If you use the parts specified below, you can expect approximately the following.:

Fog duration between less than 1 second to about 10 seconds.

Interval timing from 1 second, to about 75 seconds.

An important note: Some of my testing shows this to be sensitive to electrical noise generated by the pump in my fogger. Specifically, if I leave the pendant right on top of the fogger, it tends to get stuck in the "on" position. I'll see if I can figure out why, and I'll update the schematic when I figure it out.

Parts List

1 NE556N Dual Timer (2 555s in a 14pin DIP)

3 220 ohm 1/8W resistors (for all resistors 1/4W will work too)

3 10K ohm 1/8W resistors

2 1M ohm single turn trimpots (or any other pot you like)

1 100uf 25V Electrolytic Capacitor

1 10uf 25V Electrolytic Capacitor

1 0.001uf capacitor

1 0.47uf Tantalum capacitor (bypass cap, hook between VCC and gnd on the 556

2 LEDs (I liked using 1 red and 1 green)

1 IRF510 MOSFET

1 6V relay (adjust to the size of your wart, of course)

1 6V wall wart (or whatever)

1 wall wart socket.

Here is the schematic I threw together. If enough people ask, I'll try and make a decent one. Ask Here make sure to put 'fogger schematic' in the subject Updated 10/09, new schematic

There is no turning back once you've done this :). Here you see the hole for the wall wart receptical. Note that all of this assembly is done in the bottom half of the remote. The part without the switch.

Here, I've mounted the LEDs and the trimpots that will be used to control the time interval. All of these parts are secured using hot glue.

Now the relay, the MOSFET is hot-glued to the relay.

Here I've mounted everything finally. I used a technique for assembly that is called "rat's nest". Specifically, there is no circuit board in there. I just did point-to-point wiring of all parts directly to the IC. The IC is then glued to the bottom of the remote box. As you can see, there is a U shaped opening. This is to give clearance to the switch already in the remote. We don't exacly want 120V on the solid state part of this, now do we? Anything that you think might short, give a glop of hot glue as insulation to.

Ok, here is the thing put back to gether. The LED and pot that control the interval are closest to where the power from the wall wart goes in. The other LED is for the smoke time.

Here, you can see the LEDs on. To tune this, adjust both pots to the minimum setting. Adjust the pot for the smoke length to the duration you like, then adjust the other to get the repeat pattern you want. The LED indicates when you are 'in' a segment. So the interval LED is on during countdown, and the duration LED is on during fogging. I used green for interval, and red for duration so I could easily remember which is which.