Hello geeks,

I am here to seek help with logic. there are two GPIO's viz, GPIO 1 and GPIO 2.

GPIO 1 turns logic 1 first (+5V) and then after 100 mSec GPIO 2 becomes logic 1 (+5V).

I want to build circuit which will blink LED for 10sec only if both GPIOs and logic 1 and then turn solid ON.

I am able to blink, but somehow not able to latch logic 1 at the output of 555 timer.

 

Sounds like a programming problem. Shall we guess what you wrote, which language, and which chip?

ps, I think we're nerds. Geeks are like circus people who bite the heads off chickens.

 

Hey nerd,

I just want simple 555 based circuit, no programming.

I have used astable multivibrator for blinking

 

Hey nerd,

I just want simple 555 based circuit, no programming.

I have used astable multivibrator for blinking

your description of what you want is not clear. Please elaborate.

 

ps, I think we're nerds. Geeks are like circus people who bite the heads off chickens.

Nerds are software. Geeks are hardware.

ak

 

Nerds are software. Geeks are hardware.

ak

I guess that makes me a geek.

 

your description of what you want is not clear. Please elaborate.

Right now, it sounds like a nand and a 556, but why not do it in software if you already have an MPU?

 

Right now, it sounds like a nand and a 556, but why not do it in software if you already have an MPU?

I'm not understanding timeline of the series of events the OP is describing. The 100 mSec vs 10 seconds and how he expects to determine the difference.

 

Right now, it sounds like a nand and a 556, but why not do it in software if you already have an MPU?

Thats the exact problem, we cant use MCU

 

I'm not understanding timeline of the series of events the OP is describing. The 100 mSec vs 10 seconds and how he expects to determine the difference.

There are two GPIO, GPIO 1 and GPIO 2.

1. Initially both are logic 0
2. First GPIO 1 becomes Logic 1
3. 100 mSec later GPIO 2 becomes 2.
4. When both the GPIO are 1, LED should blink for 10sec
5. After 10 second LED should stay ON

 

There are two GPIO, GPIO 1 and GPIO 2.

1. Initially both are logic 0
2. First GPIO 1 becomes Logic 1
3. 100 mSec later GPIO 2 becomes 2.
4. When both the GPIO are 1, LED should blink for 10sec
5. After 10 second LED should stay ON

If you are driving the LED with the 555 and both 555 must be logic 1, there is no way to make the LED flash, right?
If both must stay logic 1 while flashing occurs, then you need additional chips or transistor's.

On the other hand, If one of the 555 can be oscillating between 1 and 0 for the 10-second flashing period, then it becomes much easier with just the two 555s (or one 556).

 

Thats the exact problem, we cant use MCU

So this is the homework for school?

 

What frequency would outC need to flash at ?
.

I would hope the flash is at 5Hz so the first high would be 100 mSec before falling low to trigger the 10 second of flashing time.

 

Hola pkatiyar,

Why do not you write a simple graphic to describe the time line of the required sequence? One line per GPx.

While you draw it you could even find the solution to your problem.

Believe me on this: managing to express properly your problem (to yourself, first of all) is the first good step to solve it.

 

So you have 2 inputs. inA & inB
One output outC

Step 0: inA=0 inB=0 outC=0
Step 1: inA=1 inB=0 outC=0
Step 2: Wait 100ms
Step 3: inA=1 inB=1 outC=0
Step 5: outC=flash for 10 seconds (while inA=1 & inB=1)
Step 6: outC=1

What frequency would outC need to flash at ?

What happens if inA or inB changes state during the flashing stage ?

If might help to drawing a timing diagram to visualise what happens before trying to design a circuit.

Yes exactly,

In between state should not impact. I used one mono stable to generate 10 sec pulse which triggers astable. The only problem is that output goes low once astable stops, since I am using reset as trigger

 

What is not clear - TS: Do GPIO 1 and 2 stay high for the entire 10 second blink time, or might they return low while the LED is blinking? A true monostable doesn't care, but there has to be a condition that resets whatever is doing the 10 s timing, and when that condition occurs is important.

Another way to go is with a counter and gating to pass 10, 1 s clock cycles to the LED, ending on a high clock phase. In this case you still need a blink oscillator, but not a monostable. 4093 + 4017, or something like that.

Or, one 4060 and some diodes. Hmmm... Is using a 555 and a monostable a requirement of this homework problem?

ak