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Time delay circuit.

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mazur50

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I am looking to make a Circuit that when you push a button it will activate a relay and a timmer. and when the time runs out it will close a relay.

I would like it to be adjustable with a pot for 0-60 min. let me know if you have any ideas. I was going to us a 555 timer but i was told it will not time for 60 min.

I am looking to make somthing like this.

**broken link removed**
 
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60min (1hr/3600secs) implies a very low frequency which implies very large values for your capacitors and resistors. What comes to my mind at this moment is a microprocessor solution. I'm afraid I can't come up with a less expensive approach. You connect the button to the interrupt pin of the microprocessor and it goes to the Interrupt Routine you've written, where it counts merrily for an hour! Not very efficient?
 
Like I said on the other website, the Qkit is made by Velleman. Velleman's datasheet shows parts that have a max time period of only 4 minutes. They lie and say 1 hour on the sales page.

The CD4060 and CD4541 oscillator/timer ICs will easily time to a hour with a small and inexpensive capacitor.
 
Cheapest, quickest solution I can think of is use this chip:

**broken link removed**

Wire a pot to it's analog input pin, start switch to a digital input pin and drive a relay with a digital output pin (low current relay or use a transistor to drive a larger relay coil).

Software is free and programming is done with just a serial cable to your PC and two resistors.

Lefty
 
You could always rig the 555 timer up to a binary counter. Make sure you set it up to reset at power-on, and then use some AND gates to produce a logic output when all of the outputs are on.

If you still can't get enough time, then you could always cascade counter circuits so that the previous stage clocks the next. If you were to set the 555 timer to produce a 1Hz output, then three 4-bit binary counters cascaded would give you ooooooh... about 4096 seconds of time?

Probably overkill, but it should work. Depends how much adjustment of the time period you want.

Brian
 
Have you done a search of this forum for "timer", there have been plenty in the past
 
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ThermalRunaway said:
You could always rig the 555 timer up to a binary counter. Make sure you set it up to reset at power-on, and then use some AND gates to produce a logic output when all of the outputs are on.

If you were to set the 555 timer to produce a 1Hz output, then three 4-bit binary counters cascaded would give you ooooooh... about 4096 seconds of time?

Probably overkill, but it should work. Depends how much adjustment of the time period you want.

Brian

Four chips in all? Perhaps my microprocessor solution wasn't expensive afterall if you add the overhead that comes with each of the four chips. There are some cheap microcontrollers around, only that using a powerful tool as a microcontroller with the sole purpose of counting time is not very efficient.

But since you haven't told us what your project is all about, there are probably other sections in your project that you can dedicate your microcontroller to.
 
What i am looking to do is make a power supply for breaking in DC motors. And i want a dial so i can set the break in time. from 0-60min. and i also want to have a plug on the front that i can plug my sodering iron into. so it will control the temp of the iron. let me know if you have any ideas for that as well.

thanks
 
aibelectronics said:
Four chips in all? Perhaps my microprocessor solution wasn't expensive afterall if you add the overhead that comes with each of the four chips. There are some cheap microcontrollers around, only that using a powerful tool as a microcontroller with the sole purpose of counting time is not very efficient.

But since you haven't told us what your project is all about, there are probably other sections in your project that you can dedicate your microcontroller to.

audioguru's solution is undoubtedly the best. For personal projects though, expense is usually a minor issue. 4 chips will be more expensive than a microcontroller, but it'll hardly break the bank. If you're making millions of them, that's a different matter.

I agree though a microncontroller would make light work of this task. Just depends if he has the ability and development tools to use one.

In any case, audioguru has pointed out a 1 chip solution with no programming involved so there's not much to debate about, I would concentrate my research there.

Brian
 
mazur50 said:
i also want to have a plug on the front that i can plug my sodering iron into. so it will control the temp of the iron. let me know if you have any ideas for that as well.

thanks

Unless you have a specific interest in developing this kind of project, I would suggest you simply buy a cheap temperature controlled iron. You're not going to make one yourself much cheaper, and you're going to need to do a lot of work to acheive the same quality as an off the shelf item.

For me, the Electronics hobby has always been about developing circuits to meet your own specific application which an off the shelf item would unlikely be able to meet. A temperature controlled iron doesn't fall into that category, there are plenty of off the shelf items which will do exactly what you need.

Brian
 
A "volume control" on a cheap soldering iron is no good. You turn it down so it doesn't get too hot then it cools when you solder so you need to turn it up.
My temperature controlled soldering iron has a temperature sensor so it is always at the correct temperature automatically.
 
The 74393 is a dual 4-bit binary counter. They are pretty cheap. All you need is a couple of these and a 555 timer.
 
A CD4060 oscillator/divider is only $.48US at Digikey.
A CD4541 is only $.55US.

They don't need a 5V regulator like old TTL needs.
 
A "volume control" on a cheap soldering iron is no good. You turn it down so it doesn't get too hot then it cools when you solder so you need to turn it up.
Also the cheap iron is creating a static charge as it goes up and down in its heating and cooling, which will, at some point, release into what you are working on. Hopefully, it won't discharge into a CMOS component.
 
aibelectronics said:
Four chips in all? Perhaps my microprocessor solution wasn't expensive afterall if you add the overhead that comes with each of the four chips. There are some cheap microcontrollers around, only that using a powerful tool as a microcontroller with the sole purpose of counting time is not very efficient.

But since you haven't told us what your project is all about, there are probably other sections in your project that you can dedicate your microcontroller to.
This can be done with 2 ICs. A counter and a Quad NAND Schmitt Trigger.

The Schmitt can be used for the power on reset and the oscillator.

Operate the relay when Q14 goes high. Connect one gate of the Schmitt as an inverter and connect it between Q14 and the other input of the oscillator gate to stop the oscillator. While Q14 is low, the oscillator is allowed to count. When Q14 goes high, the oscillator stops.

If you don't understand this, let me know and I'll post a circuit. Don't forget to insert 100 nF bypass capacitors on the supply line.
 
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The CD4060 oscillator/divider IC need a resistor and a capacitor to reset it when power is applied.
The CD4541 oscillator/divider automatically resets itself when power is applied.

Why use a counter IC plus a gates IC?
 
1. I prefer to use a Schmitt for the power on reset for the 4060.

2. I have not studied the 4541, so I did not realise it has internal power on reset. That's good to know.
 
Here is a suggestion as requested in your PM
 

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