My sons want to accomplish similar science projects. (The practical use of the projects is to time-limit gaming during a 24 hour period.)

For the younger son, we want to configure relay and off-the-shelf timers to limit play to 2 hours per 24 hour period. We prefer to use a momentary contact switch for the trigger, but are now using a 2 hour spring timer. We are having trouble with the 22 hour "lock out" period. Any help will be appreciated!

My older son wants to build a circuit board that does the same thing. We have looked at a "repeating interval timer" design from the internet. It looks ok, but one of the resistors is labelled "4k7". Any idea what that is?

Also any other drawings would be helpful.

Thanks in advance.

 

4k7 = 4700Ω = 4.7kΩ It's just easier to read in case the period gets rubbed off... A multimeter check will verify...

 

You may need to think a bit more clearly about what your goals are. You talked about a 22 hour lock out period, but that is assuming that the 2 hours of gaming was done all at once. What if he played for an hour, then ten hours later played for another half hour, then ten hours after that played for another half hour? At the enf of that final play period he has played two hours in the past 24, but in another couple hours he will have played only one hour in the past 24. How do you want that handled? It's not critical that it be done "right" (though it may be the basis of some bickering if it isn't "right"), but it is important that a decision be made at some point. Otherwise, you will be attempting to solve a problem without even understanding what constitutes an acceptable solution. But that doesn't mean that you have to stick to whatever definition of a solution you first come up with -- you can always tweak it (or completely revise it) as you start finding out what solutions are and are not practical. For instance, if you find a timer that can be set for two hours and then counts down but that that you can pause without resetting, you can declare that the timer will be reset the first time game playing starts on a given day (i.e., after midnight) and once it expires all game play is done until midnight again. Yes, this leaves the possibility that someone could play for four hours straight (the last two hours of one day and the first two hours of the next), but they will still be limited to an average of only two hours per day. So perhaps letting this kind of "binge" be possible is not a bad thing.