key bleep

elektorjuly /august 1983 104 key bleep There are many situations where an audible indication for a button pressed would be very useful. Two particular cases are: a morse key, where it is otherwise impossible to know that the key has been operated, and an ASCII keyboard. This circuit is based on a 7555 timer IC (the CMOS version of the well known 555) which is connected as an astable multivibrator (AMV). Its output is a square wave at a frequency of about 700 Hz and is used to drive a smal) buzzer. The circuit will be prevented from oscillating if pin 4 of the IC is taken to 0 V, in other words, a short between points A and B in the circuit diagram. R2 ó IC1 TS 00k p 7555 63 BC 547B C, c _ R= TM BC547B As mentioned, the key bleep is ideal for use as a key push indicator with the ASCII keyboard. In this case a tone will be produced each time the key is pressed making it unnecessary to continually look at the screen to verify correct operation Don"t worry, only one key bleep circui...