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I want to make this: http://www.uoguelph.ca/~antoon/circ/555test2.htm
But what will happen if I press swish S1 and keep it
closed? Are the leds just going on once or will they go off
and after 2,5 seconds on again.
And so making a continues loop?
All three of these 555 timers are connected as monostable multivibrators; so a single cycle will be seen rather than continuous. The switch [S1] simply kills the power to the monostab IC3 and the 74107 IC5.
This means that ICs 1&2 will time out soon after power is applied to the circuit and then sit dormant until power is isolated and restored :?: regardless of the position of S1.
The only way I can see this circuit working is if S1 kills the power to everything (an on-off switch) :?
Although this way of testing a 555 seems OK it doesn't check the discharge transistor. I wonder if a simple astable circuit would be more thorough - it would just mean watching an LED to observe flashing for OK or steady for faulty.