Creating a Timing Circuit (LM555) with Adjustable T1 & T2

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In summary: It has many uses and is relatively easy to work with.In summary, the 555 timer circuit can be adjusted to have a time duration of up to 40 minutes, but a better solution is to use a digital oscillator.
  • #1
JO3
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Hello all,

I'm trying to make a circuit with the following properties:

1) output at +V for a time T1
2) output at 0 for a time T2
repeat indefinitely
**also, whenever contact is made between two points, I would like the circuit to jump to state 2 (contact would only be made when the system is in state 1)

It would be good if I can adjust T1 and T2 continuously, i.e. with a variable capacitor and/or potentiometer. T1 should be about 15 minutes and T2 should be about 45 minutes, but I want to understand the circuit enough to be able to make adjustments myself. Equations would be very helpful:)

I think I might be able to use the http://www.national.com/ds/LM/LM555.pdf" [Broken]chip, but I'm not exactly sure how to set these up. Voltage should be between 5V-15V or so.

Thanks for your help,
Joe
 
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  • #3
Thanks, that site looks very helpful. I'm reading through it now.

Joe
 
  • #4
JO3 said:
It would be good if I can adjust T1 and T2 continuously, i.e. with a variable capacitor and/or potentiometer. T1 should be about 15 minutes and T2 should be about 45 minutes, but I want to understand the circuit enough to be able to make adjustments myself. Equations would be very helpful:)

Those are pretty long times to be trying to use a 555 analog timer circuit. A better solution would be to use a digital oscillator (based on a 32kHz watch crystal, for example), with divider circuits and a little logic to give you the variability you want. Check out the 74HC4060 IC and its app notes, for example.
 
  • #5
WOW! I thought I was pushing the envelope timing out to around 10 minutes with a 555.
 
  • #6
I got one to go to 40 minutes. It's in a coffee-cup heater, the heater shuts off after the 555 says it's time.

The heater circuit originally timed out at 20 minutes. I opened it up, changed a 5M resistor to 10M, and now it's 40 minutes.
 
  • #7
I've had them work for long times also. Nice big caps.
I think that the 555 is a good way to get your feet wet in circuit building.
 

What is a timing circuit (LM555)?

A timing circuit, also known as an LM555, is an integrated circuit that is used to generate precise time delays or oscillations in electronic devices.

How do you create a timing circuit with adjustable T1 and T2?

To create a timing circuit with adjustable T1 and T2, you will need to use a LM555 integrated circuit, a resistor, a capacitor, and a potentiometer. By adjusting the values of the resistor and capacitor, you can control the length of time for T1 and T2, respectively. The potentiometer can be used to fine-tune the timing circuit.

What is the purpose of T1 and T2 in a timing circuit?

T1 and T2 are the timing intervals in a timing circuit. T1 controls the length of time for the output to be high, while T2 controls the length of time for the output to be low. By adjusting these intervals, you can create specific time delays or oscillations for your electronic device.

What are some common applications of a timing circuit (LM555)?

A timing circuit (LM555) can be used in a variety of electronic devices such as timers, oscillators, LED flashers, and pulse generators. It is also commonly used in robotics, automotive systems, and communication systems.

What are the advantages of using a timing circuit (LM555) with adjustable T1 and T2?

The main advantage of using a timing circuit with adjustable T1 and T2 is its versatility. By being able to adjust the timing intervals, you can customize the circuit to meet the specific needs of your electronic device. Additionally, the LM555 is a low-cost and widely available integrated circuit, making it a popular choice for timing circuit applications.

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