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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.
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
The number on the display will not disappear if you connect Pin 14 of U1 to Pin 3 of the 555.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
cannibal,matk95 said:if the 4026 is not avilible in your county then try using cmos 4029 and 4511 to make the counter
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.Hero999 said:no one bothers with logic gates anymore and this is why they are hard to get hold of.
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.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.
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.
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.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 !!!
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.