How can I prevent my NE555 timer from being triggered upon power ON?

  • Thread starter Mike Phan
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In summary: The circuit is designed to hold the NE555 in the reset state for 2 seconds. If you try to modify pin 4 as I mentioned before, it still doesn't work. I am thinking that the values of resistor and capacitor are not correct. Do you think so? In summary, the circuit is using a NE555 timer to active a solenoid driver. When the power is turned on, the circuit is initially running. The purpose of this is to delay reset pin a while after the power switching ON which cause a "voltage spike" and stimulate pin2 (trigger). Mike Phan suggests changing the values of the resistor and capacitor to solve the problem.
  • #1
Mike Phan
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Hi,

My circuit is using NE555 timer to active a solenoid driver for some seconds. I have finally found out that any time we turn the power ON, the circuit is initially running. I have wondered that, when we turn the power ON, the power switch creates a signal as a voltage, so that can stimulate the NE555 trigger (pin #2) then run the solenoid driver.

Questions:
1. What kind of that signal?
2. How to solve that problem?

Thank you all.

Mike Phan
 
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  • #2
Post your complete circuit. What are you doing with pin 4?
 
  • #3
Pin 4 is connected to Vcc.
 
  • #4
It's been a while since I worked with a 555 so I'm just going by memory on the pinout. I believe pin 4 is a reset pin. Connect it to Vcc through a resistor and ground through a capacitor. This will cause the pin to be grounded briefly at power up which causes the 555 to go reset. Choose your resistor and capacitor values based on how long you want the 555 to be held in the reset state.
 
  • #5
You are right, pin 4 is a reset. My 555 is deisgned to hold for 2 seconds. I have tried to modify pin 4 as you just said. Let me double check: connect it to Vcc through a resistor 10M ohm, and gorund it (pin 4) through a 4.7uF capacitor. It is still problem! I am thinking if the values of resistor and capacitor are not correct. Do you think so?

Mike Phan
 
  • #6
1 RC time constant at those values is 47 seconds. A bit long don't you think?
 
  • #7
Do you know how to attach a file? I want you to see my circuit.

The purpose of this is to delay reset pin a while after the power switching ON which cause a "voltage spike" and stimulate pin2 (trigger), right?

What is your suggestion? Thanks and I am waiting for your reply.
 
  • #8
If the NE555 is a bipolar version of the 555 family, 10MegOhm is too big for an input resistor. Look up the input bias current on the inputs. If you use a CMOS 555 like the Philips ICM7555, the input bias current is in the 10pA range, and 10MegOhm would theoretically work (although it is poor design practice to use resistors that big -- quiz question: Why is it poor design practice?).

Here's a good tutorial on 555 operation -- do you get waveforms similar to those shown here?

http://www.uoguelph.ca/~antoon/gadgets/555/555.html
 
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  • #9
Make sure to hold the trigger pin high with a 10k ohm resistor (depending on voltage). This way the trigger isn't as sensitive to stray pulses that maybe be caused from the circuit being energized.
 
  • #10
Thanks Triden and others. It has been done already.

Mike Phan
 

1. What is a NE555 timer trigger problem?

A NE555 timer trigger problem refers to any issues or malfunctions that may occur with the NE555 timer, a commonly used integrated circuit (IC) in electronic circuits. The NE555 timer is used to generate precise and stable time delays, oscillations, and pulses, and a trigger problem can disrupt the normal functioning of the circuit.

2. What are the common causes of NE555 timer trigger problems?

The most common causes of NE555 timer trigger problems include incorrect wiring or connections, damaged components, incorrect component values, and power supply issues. Environmental factors such as temperature and humidity can also affect the performance of the NE555 timer.

3. How can I troubleshoot a NE555 timer trigger problem?

To troubleshoot a NE555 timer trigger problem, start by checking all connections and components for any damage or incorrect values. Make sure the power supply is stable and within the required voltage range. You can also use a multimeter to measure the output of the NE555 timer and compare it to the expected values. If the issue persists, consult the datasheet for the NE555 timer for further troubleshooting steps.

4. Can a NE555 timer trigger problem be fixed?

In most cases, a NE555 timer trigger problem can be resolved by identifying and addressing the underlying cause. This may involve replacing damaged components, correcting wiring or connections, or adjusting the power supply. However, if the NE555 timer itself is faulty, it may need to be replaced.

5. How can I prevent NE555 timer trigger problems in the future?

To prevent NE555 timer trigger problems, it is important to handle and store the NE555 timer and other components properly to avoid damage. Double-check all connections and component values before powering on the circuit. It is also recommended to use a stable power supply and to follow the manufacturer's guidelines for using the NE555 timer.

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