U1 = LM555 timer/oscillator
U2 = 74LS190
U3 = 74LS42
U4 = 74LS76
P1 = 10K, potentiometer
R1 = 10K
R2-R11 = 220 ohm
C1 = 100nF, ceramic
10 LED's, ultra-bright
U1, the 555 timer/oscillator clocks a 74LS190 up/down counter (U2). The 74LS190 drives a BCD decoder driver 74LS42 (U3).
The 74LS76 has as task to reverse the count on 0 to 9 to 0 and so on. P1 sets the up/down counter speed. R2 to R11 are
all 220 ohm carbon-type resistors.
You may have noticed in the diagram it does not specify the 'LS' (Low Schottky) IC types but done for simplicity
reasons. If your circuit is powered from a battery you definately should use the LS versions as the current draw is
significantly less and so your battery pack will last longer. Same for the 555; use the cmos version to cut down on
Click here LM555 for more information and data on the 555 timer/oscillator IC.
Keep wires as short as possible since too long wires may be a cause for interference (RFI).
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Copyright ©1993 -- Tony van Roon