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.


JF