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

  • Thread starter Thread starter JO3
  • Start date Start date
  • Tags Tags
    Circuit
Click For Summary

Discussion Overview

The discussion centers around creating a timing circuit using the LM555 chip, specifically focusing on achieving adjustable timing intervals T1 and T2 for an indefinite cycle. The inquiry includes the desire for continuous adjustment of these intervals and the implementation of a contact-triggered state change in the circuit.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Joe outlines the requirements for a timing circuit using the LM555, specifying the need for adjustable timing intervals T1 (approximately 15 minutes) and T2 (approximately 45 minutes), and expresses a desire for equations to understand the circuit better.
  • One participant suggests that using a digital oscillator with a 32kHz watch crystal and divider circuits might be a better solution for achieving the desired timing intervals, referencing the 74HC4060 IC as an alternative.
  • Another participant shares their experience of successfully using the LM555 for timing intervals up to 40 minutes in a coffee-cup heater application, indicating that it is possible to achieve long timing intervals with appropriate component adjustments.
  • A different participant mentions having also achieved long timing intervals with the LM555 by using larger capacitors, suggesting that the chip can be a good starting point for beginners in circuit building.

Areas of Agreement / Disagreement

There is no consensus on the best approach to achieve the desired timing intervals, with some participants advocating for the LM555 while others propose using a digital oscillator. The discussion reflects a mix of experiences and suggestions without a definitive resolution.

Contextual Notes

Participants express varying opinions on the feasibility of using the LM555 for long timing intervals, with some citing successful implementations and others suggesting alternative methods. The discussion does not resolve the potential limitations of the LM555 for the specified timing requirements.

Who May Find This Useful

This discussion may be useful for individuals interested in circuit design, particularly those exploring timing circuits and the capabilities of the LM555 chip versus digital alternatives.

JO3
Messages
2
Reaction score
0
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" 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
 
Last edited by a moderator:
Engineering news on Phys.org
Thanks, that site looks very helpful. I'm reading through it now.

Joe
 
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.
 
WOW! I thought I was pushing the envelope timing out to around 10 minutes with a 555.
 
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.
 
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.
 

Similar threads

Queries related to buck converters
  • · Replies 14 ·
Replies
14
Views
3K
What explains the current flow in a LC circuit?
  • · Replies 4 ·
Replies
4
Views
3K
Circuit analysis via polyhedron
  • · Replies 5 ·
Replies
5
Views
2K
Does Adjusting Potentiometer Resistance Affect Volume in Amplification Circuits?
  • · Replies 8 ·
Replies
8
Views
3K
Troubleshooting Op Amp Attenuation in Gain-Adjustable Amplifier Circuit
  • · Replies 14 ·
Replies
14
Views
2K
How Can I Create an Adjustable Optical Switch Circuit for an Inductive Load?
  • · Replies 3 ·
Replies
3
Views
4K
Engineering How to solve a circuit mystery box?
  • · Replies 16 ·
Replies
16
Views
4K
Eddy current position sensor circuit
  • · Replies 5 ·
Replies
5
Views
3K
Undergrad Warm-up time for a hollow cylinder
  • · Replies 5 ·
Replies
5
Views
3K
How Should I Set the Time Constant for LPF/EWMA?
  • · Replies 1 ·
Replies
1
Views
3K