Timer 555
Compteur 10 minutes

Fig. 8 Ten-Minute Timer:

Can be used as a time-out warning for Ham Radio. The Federal Communications Commission (FCC) requires the ham radio operator to identify his station by giving his call-sign at least every 10 minutes. This can be a problem, especially during lengthy conversations when it is difficult to keep track of time.

The 555 is used as a one-shot so that a visual warning indicator becomes active after 10-minutes. To begin the cycle, the reset switch is pressed which causes the 'Green' led to light up. After 10 minutes, set by the 500K potentiometer R1, the 'Red' led will light to warn the operator that he must indentify.