Capacitors

42 = 42 pico-farad
103 = 10 x 10³ pico-farad = 10,000 pf = 10 nf
104 = 10 x 10⁴ pico-farad = 100,000 pf = 100 nf = 0.1 uf
105 = 10 x 10⁵ pico-farad = 1,000,000 pf = 1000 nf = 1 uf
Positive lead is usually longer; Negative lead may have mark. more...

7400 TTL

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LEDs

Longer lead is positive.
Flat edge inside (if visible) is usually negative.

Tester

Clock generator

Normal clock

http://www.uoguelph.ca/~antoon/circ/clock1.htm

Excellent clock generator to drive 4017 type cmos circuits.
R1 = 10K to 10M, C1 = 100pF to 47uF.
Fo is ±1Kz when R1=100K and C1=10nF.
Input voltage can be from 5 to 15V.

Single-step clock

Reset

Notes

20081130 - Why does the simple clock circuit based on 74LS00 not oscillate?