hit the number

Posted on Feb 4, 2014

One PIC to act as a keypad driver though plus some primitive stuff to tie them together (when the time runs out disable the keypad and beep, when the correct button is pressed increment the score counter and regenerate). The random number generator is really bad. It relies on the inaccuracy of RC timing circuits! You have two 555 chips, one is set as a very fast astable (oscillator), the other as a much

hit the number
Click here to download the full size of the above Circuit.

slower monostable (switches "on" for a while when the input is pulsed before switching itself off again). The output of both is ANDed and sent to the clock of a counter chip, so when the monostable`s input is triggered the counter counts up very quickly for a short space of time before the monostable switches off again and there`s your "random" number. The `8` and `2` outputs of the counter are ANDed together and connected to the reset pin, so when the counter reaches 10 (8+2) it automatically resets to 0. Click for a circuit diagram. In the photo, the two small 8-pin chips are evidently the 555s, and I guess that the chip on the right is the 7-segment display decoder, the one to the left of that is the counter and the second left chip is a series of AND gates. The logic is this; it sets the rows of the keypad high, then checks the columns until it finds one that`s connected, at which point it outputs the result. If no key is detected it outputs %1111. It also checks if the "random" pin is high (this signifies a new random number is being generated) and if so it outputs %1111 anyway. In the bottom-left of the photo is the logic to detect when to increment the score (it checks if the current value isn`t %1111 - that is, it only accepts a "correct button" result if the button isn`t %1111, which indicates no button pressed). If all is hunky-dory it triggers a monostable to fire once (the 555 next to it) which increments the...

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