You actually need an astable, not a monostable for this - an astable gives a continuous pulse.
You should be able to achieve a long delay with a moderate sized timing capacitor and large timing resistance, but watch out for capacitor leakage exceeding the charging rate for some large capacitors. I've had this problem recently with a 555 monostable circuit and stops the monostable from switching off.
However, do you really need a large delay for your application - surely a regular (say every 10 sec) pulse would also keep the calculator in the ON state?
Also, how are you going to get the 555 output to 'press' the On button on the calculator? By electrical or some machanical means?
Also, on most calculators, the On button doubles as the 'clear' button, so it might interfere with your calculations!
Hope this gives you some help and some thought - I look forward to your reply! |
