The Maplin Electronic Circuits Handbook, 2nd Edition

162 TIMERS

4k7

10η

0

Trigger

input

Figure 7.9 Improving the trigger

sensitivity of

a

555 timer by

reducing quiescent d.c. voltage

present at the trigger input

Figure 7.10 Improving the

trigger sensitivity using an

additional transistor. (Note that

this arrangement triggers on a

positive, rather than negative,

going edge)

pulse. It should be noted that, in common with most timer circuits,

adequate decoupling of the supply rails is essential in order to reduce the

amplitude of supply borne transients. Such decoupling should normally

take the form of an appropriate value capacitor (as a general rule of thumb

this should be at least ten times th ...