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Could use assistance on a timer project

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audioguru

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The 555 is either a monostable timer or it is an astable oscillator. Your circuit is not an astable unless its power supply is motorboating.

If pin 2 is low then it never times out, its output will stay high.

Pin 4 is the reset pin. When pin 4 is low then the IC is continuously reset with its capacitor discharged and its output low.
When pin 4 is high then the timer works normally.

Your circuit is missing two very important supply bypass capacitors. The datasheet for an ordinary 555 recommends using a 0.1uF ceramic disc plus a minimum of 1uF electrolytic (use 10uF to 100uf).
 

warlc

Member
hi audioguru,
which circuit are you referring to? the one that has pin 4 connected to the 100k resistor or the l;atest one i attach that has pin 2 edge triggered
 

audioguru

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Your latest circuit has the pin4 on the 555 floating so it might be intermittent.
Pin4 needs to be high for the timer to work or be low for the timer to be reset.
Its pin 2 is always high so the 555 won't do anything.
 

warlc

Member
I brought pin 4 high. the circuit times the same way regardless of whether pin 4 was used or not. my problem is , how can i invert the ouput of the 555 so when its timing (24 sec) the relay is "off" then a 1 sec "on". I had this function in the other circuit but i couldn't make the edge trigger work on that one. and how do i connect the opto to pin 2, a transistor?
 

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  • timer555-6.JPG
    timer555-6.JPG
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audioguru

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You now have a 24 seconds timer. Connect pin4 to the positive supply so it doesn't trigger intermittently. Add another 1 second 555 timer to turn on the musical thing after the first 555 times out.

The collector of the opto goes to ground when its LED is powered and it can edge-trigger the two resistors and a capacitor at pin2.
 
Last edited:

warlc

Member
please bear with me, if i swap the contacts on the relay for the actuator (nc instead of no contact) wouldn't the actuator spike when the power was applied? I would like to try this without another 555. i had a "pulse" "pause"
that worked in the other circuit

the opto would be wired as shown?

I have attached a mechanical version of what i'm trying to do
 

Attachments

  • clktimer.pdf
    9.1 KB · Views: 94
  • clktimer mech.pdf
    8.3 KB · Views: 90

audioguru

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You have the "edge trigger" input of the 555 circuit connected to the opto's emitter (0V) instead of to its collector. Its emitter does nothing.
Then the 100k resistor can be removed since the first 10k resistor in the "edge trigger' circuit replaces it.

Use a "power-on-reset" resistor and capacitor at the 555's reset pin to stop it from timing when power is applied.
 

warlc

Member
thank you audioguru,
I decided to go with a 556 timer that will give me the two time delays.
I added the changes you suggested into this circuit. I hope I have the pinouts shown correctly (I used a circuit with two 555's). I received the opto sensors today, so i'm going to incorporate everything unto one breadboard and see how that works out.
thank you for your help
 

Attachments

  • 556clktimer.pdf
    8.6 KB · Views: 133

audioguru

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A quick glance showed the collector of the opto transistor shorted to the anode of the LED in the opto.
 

audioguru

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Pin 8 of the 556 is the trigger input of the second timer. It won't work without a resistor to the positive supply.
Pin 10 is the reset pin of the second timer. it might be intermittent without a resistor to the positive suppply then a capacitor to ground will provide power-on-reset like at pin 4 for ther first timer.
 

warlc

Member
hi
I made the changes you suggested. You mentioned about the short circuit
from the collector of the transistor to the anode of the led(in the opto). I'm not sure what you mean by that. I have attached Vishay specs on the opto and on page 3 it shows a test circuit. It didn't show +5v to the led and that confused me.
 

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  • 556clktimer.pdf
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  • visahy opto.pdf
    134.8 KB · Views: 112

audioguru

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I explained what is shorted to what.
Here are arrows in your schematic:
 

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  • musical thing with delay.PNG
    musical thing with delay.PNG
    36.5 KB · Views: 86
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warlc

Member
I have the circuit breadboarded. When I first turn it on, I get a the relay on briefly then the 556 times out and turns on the relay. I can't get it time again until I shut it down and turn it back on. I tried taking pin 6 to ground but nothing. Any ideas?
 

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  • 556timer.jpg
    556timer.jpg
    74.7 KB · Views: 69

audioguru

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The value of the capacitors on the reset pins are very low at only 0.01uF. Try 0.1uF.
When pin 6 is grounded for a moment then the timers should work again.
 

warlc

Member
it works better with .1uf caps but it's not triggering from the opto.
I'm only getting .08 volts from collector of opto to ground. I tested the opto with an led and it works fine.
 

audioguru

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Most Helpful Member
When the opto is turned off, its collector should be at the supply voltage. When it is turned on, its collector voltage should be 1V at the most.
It must turn on very quickly for it to pass a pulse though the coupling capacitor.
 

warlc

Member
I'm looking at the voltage on my supply (4 c cells) and they are at just 6 volts. That's a lot of drain in the short time i've been playing around with these circuits. maybe i'm wasting my time developing this circuit just to have the final result go through batteries every week. Using a wall transformer to power it is not an option (clocks are on mantels and are difficult to plug in)
I'm working the two circuits together (mechanical and 556) to determine which one will be the best.
The motorized timer will draw much less amps (.01 A)running (.03 start) It would require less parts. I would need a 1 or 2 sec pulse to turn on the relay. (low threshold voltage mosfet or transistors?)
What do you think?
 

warlc

Member
I'm looking at the voltage on my supply (4 c cells) and they are at just 6 volts. That's a lot of drain in the short time i've been playing around with these circuits. maybe i'm wasting my time developing this circuit just to have the final result go through batteries every week. Using a wall transformer to power it is not an option (clocks are on mantels and are difficult to plug in)
I'm working the two circuits together (mechanical and 556) to determine which one will be the best.
The motorized timer will draw much less amps (.01 A)running (.03 start) It would require less parts. I would need a 1 or 2 sec pulse to turn on the relay. (low threshold voltage mosfet or transistors?)
What do you think?
 

audioguru

Well-Known Member
Most Helpful Member
Alkaline battery cells are 1.5V each when new. Then four in series makes 6V when they are new. Your battery voltage did not drop yet.

The IR LED is about 1.2V then the 50 ohm current-limiting resistor sets its current to 96mA which might kill the IR LED and will quickly kill your battery.
 
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