文档介绍：555 Timer Go-No/Go tester. 555, 741, PLL, capacitors, resistors, Tutorials with examples
Parts List
R1 = 2M2 IC1,IC2,IC3 = 555 Timer/Oscillator
R2 = 3K IC4 = SN7400
R3,R5 = 270 ohm IC5 = SN74107
R4 = 500K Led1,Led2 = 5mm, Red/Green, high brightness
R6 = 220K S1 = On-Off switch, push button
P1,P2 = 500K, Trimpots
C1 = 1µF, 10V
C2,C3 = 4µF, 10V
Description:
This is a more advanced unit with a precise timed testing procedure.
R1 (2M2) is same as MegOhm.
The two timers determine the allowable accuracy for the timer IC under test. Potentiometers P1 and P2 permit ready
adjustment for the desired range.
With power applied, all timers switch to the high state and begin their cycles. The output of IC1 inhibits the flip-flop for
the interval T1. At T2, the output of IC2 goes low and inhibits any signal from the timer under test. The period between
T1 and T2 is the time alloted for IC3, the timer under test, plete its cycle and produce a low output. Only during
this time can a high-to-low transition from IC3 trigger the Flip-Flop IC5 so that Led 1 (timer ok), which indicates a
good IC, lights up. Led 2 lights up when the test pleted.
Although there can be a few milliseconds of contact bounce when S1 is first closed, thereby causing a delay in capacitor
charging, the delay appears across all of the IC's. But since the ratio of delay times among all three timers is the same,
the effect on test accuracy is nil.
How you get to the 5 volt supply power is up to you. Supply power should be between (min) and (max).
/~antoon/circ/ (1 van 2)18-1-2005 11:56:55
555 Timer Go-No/Go tester. 555, 741, PLL, capacitors, resistors, Tutorials with examples
Probably three alkalines will total about because they are never exactly V but always between and
or so, and will do the job until the voltage drops below . A simple stabilized 5V power supply would be
better choice, or use a 5 volt regulator with