74HC221 application

In comparison with using MC4011 NAND gate and tie two NAND gate forming
a flip-flop as data selector. 74HC221 has alreday build in dual
mono-multivibrator is much easier. Is that true?

 

[John Fields]

On 26 Aug 2005 20:09:17 -0700, mingyan_chow@yahoo.com.hk wrote:

In comparison with using MC4011 NAND gate and tie two NAND gate forming
a flip-flop as data selector. 74HC221 has alreday build in dual
mono-multivibrator is much easier. Is that true?

---
Maybe. What are you trying to do?

--
John Fields
Professional Circuit Designer

 

What I am trying to do is simply a data selector. Either a or b. In
order to drive red or yellow LED and select a or b oscillator(MC4060),

 

[John Fields]

On 27 Aug 2005 08:15:04 -0700, mingyan_chow@yahoo.com.hk wrote:

What I am trying to do is simply a data selector. Either a or b. In
order to drive red or yellow LED and select a or b oscillator(MC4060),

---
This should work:

(View using a non-proportional font like Courier:


Vcc
|
[R]
|
|A
[LEDB]
|
|
OSCA>---|-----------A
_ | nand Y--+
A/B>----+-----------B |
| +--A
+--A nand Y--->OSC OUT
|nand Y--+ +--B
+--B | |
+--A |
|nand Y--+
OSCB>------------|--B
|
[LEDA]
|A
|
[R]
|
Vcc

The gates are all NANDs (a quad dual input nand like a 74HC00 will
give you all the gates in a single package) and comprise a 2 line to
1 line multiplexer.
_
When A/B is high, the signal appearing on OSCA will appear at OSC
OUT and LEDA will light. If you use a 5V supply, HC logic and
high-efficiency LEDs, like an HLMP-4700 for the red and an HLMP-4719
for the yellow, the current limiting resistors will be:


Vcc - Vf 5V - 2V
R = ---------- = --------- = 1500 ohms
If 0.002A
_
When A/B is low, the signal appearing on OSCB will appear at OSC OUT
and LEDB will light.

--
John Fields
Professional Circuit Designer