YAG ::= Yet AGAIN
Hi Gang! I need some help with a NE555. I'm looking for a SLOW flasher preferably about 0.5 sec on and then off for 0.5 seconds. So my brain is getting rusty. A 1-second astable oscillator with a 50% duty cycle. This flasher is for a warning lamp in a flight simulator and this flasher runs for about 6 - 10 seconds only, while the landing gear is in motion.
The lamps are being driven by an MCP23017 the red lamps need two lines ON and BLINK which are selected via a 74LS32 please note the other part is a tri-state buffer (non-inverting) which is enabled via the NE555. The output of the 74ls32 drives an optocoupler which is connected to the 28vdc lamp. The circle below is the NE555.

 

If you have a tristate output, then when the output is disabled, the input to that OR gate is floating, so you don't know what state it is in (unless it is a TTL family, in which case it should float to a HI value).

 

Here's the 555 circuit.

Not sure why you need the buffer chip.
Why can't the "Blink Red" signal enable the 555 circuit which connects to the 74LS32?
Note: When enabled the first output pulse is appx 1 second long.

 

Do you even need the 74LS32 ?
BR = Blink Red
SR = Solid Red
OUT = Output of NE555

 

Here's the 555 circuit.
View attachment 299877
Not sure why you need the buffer chip.
Why can't the "Blink Red" signal enable the 555 circuit which connects to the 74LS32?
Note: When enabled the first output pulse is appx 1 second long.
View attachment 299878

Good Question: Short answer is I need to control 3 red lights separately and they have 3 states OFF, ON, BLINK.
So here's the logic
ON OFF BLINK
RED H L X
555 output The Tri-state enables pulses H to L continually
BLINK L H

so when RED=H red light lights
when RED=L red light off
when BLINK=L red light off
when BLINK=H + 555 is High which enables the buffer the selected red light BLINKS!
~~ CAH (get it?) Thanks for the help.

 

Good Question: Short answer is I need to control 3 red lights separately and they have 3 states OFF, ON, BLINK.
So here's the logic
ON OFF BLINK
RED H L X
555 output The Tri-state enables pulses H to L continually
BLINK L H

so when RED=H red light lights
when RED=L red light off
when BLINK=L red light off
when BLINK=H + 555 is High which enables the buffer the selected red light BLINKS!
~~ CAH (get it?) Thanks for the help.

This is very confusing.

You say that when RED is HI, that the red light lights and that when RED is LO, the red light is off. That covers everything -- it does not allow for any other behavior.

It might help to consider that (unless it is some special light module with appropriate inputs) as far as the light itself is concerned, "blink" is not a state. The light is either ON or it is OFF. Your logic determines which of those two states it is in.

It sounds like you have two control inputs -- RED and BLINK. Is that correct?

It sounds like (reading between the lines), if RED is HI, you want the lamp on regardless of what the BLINK input is. Is that correct?

If the RED input is LO, it sounds like, perhaps, you want the link to blink IF the BLINK input is HI, otherwise you want it OFF? Is that correct?

If so, then the following Truth Table might serve your needs:

The first two columns are your inputs. The third is the output state of a free-running 555. The final column is the state of the lamp.

RED BNK 555 | LAMP
 L   L   X  |  OFF
 L   H   L  |  OFF
 L   H   H  |  ON
 L   L   L  |  ON

Does this look like it captures the behavior that you are looking for (don't worry about how to implement it yet -- no point in doing that until we are all on the same page with regards to the desired behavior).

 

so when RED=H red light lights
when RED=L red light off
when BLINK=L red light off
when BLINK=H + 555 is High which enables the buffer the selected red light BLINKS!

In order to blink the RED must also be LOW.
Then you don't need the buffer chip as this circuit follows the same logic.
Or are you saying you want to use only one 555 circuit and gate the output as needed?
In that case a pull down resistor may be required on the output of the buffer.