Troubleshooting 555 Timer Output to 2/3 Vcc

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In summary, the speaker is experiencing issues with their 555 timer circuit, as the output voltage is not reaching the desired level and is affecting downstream components. They are seeking advice on how to troubleshoot the issue, including checking power supply rails and the possibility of using a pull-up resistor. It is suggested to double check the power supply and for any potential short circuits, and to try a different 555 chip. It is also noted that TTL counters may have different voltage requirements and power consumption.
  • #1
wolfram74
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I've got a 555 timer wired up like in this picture
10msdad.jpg

and my output is going to 2/3 Vcc instead of Vcc. This is leading to problems as I have hooked into a decade counter down the line which gets the low timer output and it's output shrinks as well. Any ideas on what I should try?
 
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  • #2
The output should be taken from pin 3. This should be a square wave which goes within a volt of the supply voltage.

It is normal to get the voltage you did from pins 2 and 6.
 
  • #3
I am taking the output from pin 3, and the output voltage is pretty much maxed out at the voltages at the max voltage on pins 2 and 6, which is about ~3.6, the Vcc is 5 and I think that's interfering with my decade counters.
 
  • #4
wolfram74 said:
Any ideas on what I should try?

Yeah, double check the power supply rails on your decade counter.
 
  • #5
Would a pull up resistor work with 555s?
 
  • #6
A pull-up would probably not work as the 555 output both pushes and pulls...

Double check your power-supply rails at the chip. Then I would check to see that you don't have a near-short on your pin 3 output signal someplace -- that could cause the output to droop. If you can, disconnect the pin from everything and see what it does. Then try a different 555 chip to see if you've managed to booger up the output driver by accident.
 
  • #7
If you are using TTL counters ( like 7490, 7493, 74192, 74193 ) then this would be normal.

These chips were OK when driving each other, but the input and output voltages were far from ideal.

A "high" was regarded as anything greater than 2.6 volts and an input actually supplied current to the device driving it.

They were also power guzzlers and many of them ran quite hot.
 

Related to Troubleshooting 555 Timer Output to 2/3 Vcc

1. How do I troubleshoot a 555 timer output that is not reaching 2/3 Vcc?

First, check the power supply to make sure it is providing the correct voltage to the 555 timer. If the power supply is working properly, the next step is to check the connections of the timer to ensure they are correct and secure. It is also important to check the values of the resistors and capacitors used in the circuit, as incorrect values can affect the output voltage. Finally, make sure that the trigger and threshold inputs are properly connected and receiving the correct signals.

2. What could cause the output of a 555 timer to fluctuate between 2/3 Vcc and a lower voltage?

This could be caused by a faulty or unstable power supply, or by a malfunctioning capacitor in the circuit. It is important to check the stability of the power supply and replace any faulty components to ensure consistent output voltage.

3. Why is my 555 timer output not reaching 2/3 Vcc even though all the connections and component values are correct?

In some cases, the load connected to the output of the 555 timer may be drawing too much current, causing the voltage to drop below 2/3 Vcc. It is important to check the load and make sure it is within the specifications of the 555 timer. If necessary, a buffer or transistor can be added to the circuit to handle the current and maintain the desired output voltage.

4. Can the 555 timer output be adjusted to a different voltage other than 2/3 Vcc?

Yes, the output voltage of a 555 timer can be adjusted by changing the values of the resistors and capacitors in the circuit. Different combinations of values will result in different output voltages, so experimentation may be necessary to achieve the desired voltage.

5. What is the purpose of reaching 2/3 Vcc in a 555 timer circuit?

Reaching 2/3 Vcc is important in a 555 timer circuit because it is the threshold voltage that triggers the timer to switch states. When the voltage at the threshold input reaches 2/3 Vcc, the output of the timer will change from high to low or vice versa. This is a key function of the 555 timer and is used in a variety of applications such as oscillators, pulse generators, and timers.

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