On Sat, 08 Nov 2008 08:05:31 -0600, John Fields
wrote:

On Sat, 8 Nov 2008 00:34:52 -0000, "IanW" wrote:


"John Fields" wrote in message
. ..

I do not see any power or ground connections to the ICs. The 74HC194s
should
have ground on pin 8 and Vcc on pin 16. The 74HC00 should have ground on
pin 7
and Vcc on pin 14.

---
Good catch.

'HC164s, BTW and, for Ian, Vcc is 5V.

So I need to step the voltage down from the 9V source, ie: about a 220ohm
resistor from the positive rail to pin 16 on each 164 and the 00?

---
I'd feel more comfortable with something like an LM78L05 in the


+----[78L05]---+---Vcc
|+ | |
BAT | [100nF]
| | |
+-------+------+---GND


But if you want to use just a resistor, then it'll need to drop about 4V
with 20mA going through it, (neglecting the current drawn by the logic
and the drop across its output) so it'll need to have a resistance of:

Vin - Vcc 4V
R = ----------- = ------- = 200 ohms
It 0.02A

so 220 is a pretty good idea.

---
I just noticed that you wanted to use one resistor per chip.

That won't work.

You need to connect all of the chips' Vcc's to one end of the resistor
and connect the other end of the resistor to +9V.

But there's a more serious problem, and that's that anytime there isn't
a 20mA load on one of the shift register outputs, Vcc will rise to ~ 9V,
which isn't a good thing.

Go with a 78L05...

JF