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Please help modified a circuit

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Thanks, I will test and write the results here :)
 

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If somebody blocks the light from hitting a photo-transistor then the 555 will not time-out and the beeper will make a noise continuously.
 
Pin 14 of U1 should go to pin 3 of IC1, not pin 2.

Also, do you realise that if one LDR is in the dark, the 555 will not be triggered if the light changes on the other one.
 
audioguru said:
If somebody blocks the light from hitting a photo-transistor then the 555 will not time-out and the beeper will make a noise continuously.

I am ok with that
but if there is a way to solve that then it's ok too to get the idea



ljcox said:
Pin 14 of U1 should go to pin 3 of IC1, not pin 2.
if I connect Pin 14 of U1 to Pin 3 of 555 then the number on the screen will disappear right ?? please correct me if I am wrong

Also, do you realise that if one LDR is in the dark, the 555 will not be triggered if the light changes on the other one.

here how it worked in my testing bredboard
LDR1 (light) / LDR2(light) then buzzer OFF
LDR1 (light) / LDR2(dark) then buzzer ON
LDR1 (dark) / LDR2(light) then buzzer ON
LDR1 (dark) / LDR2(dark) then buzzer ON
 
We showed you a few weeks ago to use a series capacitor to couple a short pulse from the collectors of the transistors to pin 2 of the 555 to trigger it. Then if something blocks the light the buzzer will beep until the 555 times out.

Pin 14 of the 74LS90 counter needs to have a low-going pulse as its clock signal. The signal feeding pin 2 of the 555 is low-going.
Pin 3 of the 555 goes high when the 555 is triggered and goes low when it times out. If pin 3 of the 555 is connected to pin 14 of the counter then the count will advance when the 555 times out.
 
cannibal said:
I am ok with that
but if there is a way to solve that then it's ok too to get the idea
See the reply by audioguru

if I connect Pin 14 of U1 to Pin 3 of 555 then the number on the screen will disappear right ?? please correct me if I am wrong
See below
The number on the display will not disappear if you connect Pin 14 of U1 to Pin 3 of the 555.
As audioguru said, the number will increment at the end of the 555 pulse.

The signal at pin 2 is too slow to trigger the counter (unless there is an internal Schmitt Trigger in it)
 
matk95 said:
if the 4026 is not avilible in your county then try using cmos 4029 and 4511 to make the counter
cannibal,
Do you know that some manufacturers sell the 4000 series CMOS devices with MC1 in front of the 4000 series number?

For example, the 4026 would be a MC14026, the 4029 - MC14029, etc.

Note that the 4511 (MC14511) has active high outputs and so it can only drive common cathode LED displays.

The 7447 has active low outputs so it can only drive common anode LED displays.

However, the 4534 (MC14543) can be configured for active high or active low, so it can drive both types of LED display. It has a "phase" pin which is set either high or low depending on which option you want.
 
Motorola I believe.

Anyway, the real way of doing this sort of thing is to use a microcontroller, no one bothers with logic gates anymore and this is why they are hard to get hold of.
 
Hero999 said:
no one bothers with logic gates anymore and this is why they are hard to get hold of.
Digikey has 874 CD4026 ICs (Texas Instruments) in the DIP package in stock today for $.75US each. They have thousands of surface-mount ones in stock today. Somebody must be using them.
 
The mind boggles, why do people use them?

It must work out cheaper in some low production run designs to not use programmable chips.
 
Hero999 said:
The mind boggles, why do people use them?

It must work out cheaper in some low production run designs to not use programmable chips.
Some people may not want to use a microcontroller, either because they want to learn about digital logic or because they are daunted by micros.

Besides, in some cases, a micro can't do the job.

I'm currently doing a design for myself in which I'm using 4 PICs and several digital ICs since the PICs are not fast enough to do some functions.
 
Hello again

I tested the circuit in breadboard

I am facing this problem

When connecting pin 14 of U1 to pin 2 of 555
the counter only shows zero and not changing also I found that the LDR should be in very dark place so the buzzer get activated

That’s why I decided to connect pin 14 of U1 to pin 3 of the 555
and the lDR is working fine and the sensitivity is perfect
but facing this problem
the counter starts from 0 zero and when the buzzer stop making sound
it shows 1 wow it counts

But here what will happen :(
when the buzzer activated again and stops the counter return to Zero !!!!

so it's like this

zero one zero one zero one

how can I make it counts zero one two three ....... and so on !!!
 

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audioguru said:
We showed you a few weeks ago to use a series capacitor to couple a short pulse from the collectors of the transistors to pin 2 of the 555 to trigger it. Then if something blocks the light the buzzer will beep until the 555 times out.

Pin 14 of the 74LS90 counter needs to have a low-going pulse as its clock signal. The signal feeding pin 2 of the 555 is low-going.
Pin 3 of the 555 goes high when the 555 is triggered and goes low when it times out. If pin 3 of the 555 is connected to pin 14 of the counter then the count will advance when the 555 times out.

Please re-read this post by Audio.

The 555 needs a pulse to trigger it.
 
cannibal said:
Hello again

I tested the circuit in breadboard

I am facing this problem

When connecting pin 14 of U1 to pin 2 of 555
the counter only shows zero and not changing also I found that the LDR should be in very dark place so the buzzer get activated See the quote from Audioguru in my post above. There is no point in us giving you advice if you don't take heed of it.

That’s why I decided to connect pin 14 of U1 to pin 3 of the 555
and the lDR is working fine and the sensitivity is perfect
but facing this problem
the counter starts from 0 zero and when the buzzer stop making sound
it shows 1 wow it counts

But here what will happen :(
when the buzzer activated again and stops the counter return to Zero !!!! See below.

so it's like this

zero one zero one zero one

how can I make it counts zero one two three ....... and so on !!!
I cannot see any bypass capacitors. You need 100 nF ceramic capacitors across the 555 (pins 4 & 1) and the U1 pins 5 & 10. I think I told you this in a previous post.

I think the reason why the counter is going from 0 - 1 - 0 - 1, etc. is because of the lack of bypass capacitors and your reset circuit (C5, R9, D2). I suspect that spikes on the +5 Volt line (due to a lack of bypassing) are causing the counter to reset via C5.
 
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The transistors are nearly overloaded by the very high input current of the old TTL counter IC. Then the gain of the transistors is very low.
When the input of the counter is removed from the outputs of the transistors then they are much more sensistive to reduced light from darkness coming.

Another reason to use a CD4026 Cmos counter IC. It has NO input current.
 
Ljcox

I used the bypassing capacitors in my breadboard us you said
and the problem is still

also I tried to remove the reset circuit (C5, R9, D2) and when the power on
I get 8 then after buzzer stop I get 9 then

8 ,9 ,8 ,9 ,8 ,9 like that

I am tired from this old TTL IC's but I can't find CD4026 in Oman
 
Connect the reset pins to ground then the counter will not reset and will count.
If the display number keeps changing then maybe the LDR is seeing a mains-powered flickering light and then maybe the counter is counting the flickering.
Then the 555 will also be triggered over and over.

Breadboards have loose connections and too much capacitance between wires for high speed TTL ICs. Use strip-board or a pcb.
 
audioguru said:
Connect the reset pins to ground then the counter will not reset and will count.
If the display number keeps changing then maybe the LDR is seeing a mains-powered flickering light and then maybe the counter is counting the flickering.
Then the 555 will also be triggered over and over.

Breadboards have loose connections and too much capacitance between wires for high speed TTL ICs. Use strip-board or a pcb.

I connected the reset pins to ground and it's true that it dosen't reset but it's also not counting only switching between two numbers
 
The output of the LDR and transistor might be to slow to clock a high-speed TTL counter. Then a Schmitt-trigger circuit is needed to feed the counter.
 
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