Tim said:
For that chip a 100nF (0.1u) ceramic up by pin 1, with a lead straight to
pin 1 and another one straight to pin 8 will be more than sufficient.
You can think about reducing them later -- but why? Unless you're trying
to shave deci-pennies off of the board cost, it's better to have too many
bypass caps than just enough.
Some general comments on effective grounding and decoupling pitched at
hobbyists (pros will know how much they can save by cutting back on
both, but for the rest of us, the small additional cost is easily repaid
by time saved debugging a glitchy circuit):
By ground, I and most other dabblers in low voltage electronics mean
chassis, common rail, 0V, battery negative, Logic negative supply etc,
NOT a hard wired connection to a copper stake in the earth.
Electricians are different - when they say ground, they mean ground!
If building on veroboard or solderless breadboard, make sure you have
reliable power and ground rails. Except in exceptional circumstances,
DONT wire them point to point. (low level audio is an exceptional
circumstance with special layout and decoupling requirements as are high
gain RF amplifiers and high power circuits in general.)
Most solderless breadboards have long rails of contact positions on each
edge, USE THEM (but beware of boards with a split between two halves of
the rail half way down it, they need a link inserted). Local decoupling
can be put over the top of critical ICs. Have an electrolytic capacitor
across the power rails where the power comes onto the board. Somewhere
between 10 and 100uF axial type is a good choice for most circuits on
breadboard.
If building digital or RF circuits on veroboard, you need a *solid*
ground rail. 2 or 3 tracks tied together at intervals along the board
is about right, or use the board crossways and run a heavy bare solid
copper buss wire along the top tacked down at intervals to any tracks
you want grounded by a little loop of bare wire over it, soldered
through two adjacent holes and to the copper buss wire.
Power rails can be done the same way but are usually less critical.
On veroboard, if you are using thin kynar wirewrap wire or similar for
your signal wires, DONT use it for power and ground.
All decoupling caps should lead as directly as possible to the ground
buss and to the + supply pin of the chip in question. 0.022uF to 0.1uF
disk or resin dipped ceramic capacitors are generally suitable for
individual chips. The chip should be located for the most direct ground
connection possible. If there is more length of wire than the width of
the board between the power supply and the board, put an electrolytic
(typically around 100x the individual ceramic capacitors) accross power
and ground where the supply wires go. Add an additional electrolytic
decoupling cap for every 10 chips.
The aim is to keep everything happily stable with respect to the ground
bus with any bounce from one IC switching *NOT* getting into other ones.
With some care with layout, bread boards are good for circuits operating
at up to a couple of MHz and veroboard up to a few tens of Mhz.
In the case of the OP's 4049 logic circuit, *ALL* 4000 series logic is
slow and low power so needs minimal decoupling. If there is no other
power consuming circuit on the board, a single 0.1uf ceramic located
centrally, WITH THE POWER SUPPLY WIRES CONNECTED DIRECTLY TO IT and as
short as possible supply and ground wires radiating to the three chips
will almost certainly be fine. If there are LEDs, a speaker or relay or
other high current loads, add an electrolytic capacitor as well.
However, I wouldn't build it that way unless I needed minimum size/weight.
If one is etching double sided PCBs or building complicated processor
boards etc., one is out of the 'dabbler' category, even if still an
amateur, so had better have a PROFESSIONAL understanding of layout
grounding and decoupling, othewise you will get PRO sised grief as
alluded to by Graham (Eeyore) in his first reply.