Hi ,

There's a stable RC oscillator is described, it's more than 5 times as stable as an oscillator built on the 555' timer:

https://www.analog.com/media/en/technical-documentation/application-notes/an12fa.pdf . Figure 15, Stable RC oscillator.

The question is concerning duty cycle of the oscillator, I need duty cycle of 50%. What is the duty cycle of the oscillator?
Many thanks in advance

 

I need duty cycle of 50%. What is the duty cycle of the oscillator?

Due to the symmetry of the threshold values of the active devices, I would expect it to be close to 50%.

If you need exact 50%, then set the clock frequency to double what you need, and run the clock output through a flip-flop configured as a divide-by-two toggle (e.g. a D-FF with the /Q output connected to the D input).
That will give 50%, independent of the clock duty-cycle.

 

The question is concerning duty cycle of the oscillator,

It's 50%. Verified on the breadboard.

 

What is interesting is that the one set of scope traces for the crystal versions looks close to 50%. But I did not see any mention of the actual duty cycles at all.
The one certain solution is already given in post #2. Other schemes may not be a close over a temperature range and with different component values.

 

The timing cycle is similar to a 555.
The voltage on the negative pin of the LT1011 is 5 volts or 10 volts depending on the output state of the inverters.
The capacitor is charging and discharging between 1/3 and 2/3 Vcc.

 

Hi ,

There's a stable RC oscillator is described, it's more than 5 times as stable as an oscillator built on the 555' timer:

https://www.analog.com/media/en/technical-documentation/application-notes/an12fa.pdf . Figure 15, Stable RC oscillator.

The question is concerning duty cycle of the oscillator, I need duty cycle of 50%. What is the duty cycle of the oscillator?
Many thanks in advance

That application note concerns the bipolar 555, which has "relatively large and unstable bipolar V CE saturation losses", so I wonder how much the situation would be improved by using a 7555.

 

Do You really need that "perfect" symmetry and stability ?

What are You building ?
.
.
.

 

That application note concerns the bipolar 555, which has "relatively large and unstable bipolar V CE saturation losses", so I wonder how much the situation would be improved by using a 7555.

CMOS timer accuracy , page 10/19 -

Low-power single CMOS timer

BJT timer accuracy, Chapter 6.5 -

LM555 datasheet(5/25 Pages) TI1 | Timer


As you can see, the accuracy is quite similar

 

Do You really need that "perfect" symmetry and stability ?

What are You building ?
.
.
.

It would be a long story...A device is needed that can detect the live cable- 230V 50Hz- deep in the walls and cable bundles.I had some practice with similar devices, and they are not very suitable for that task.A specific, separate cable must be found among other live cables.
The idea is that a load is connected to the end of the cable, which consumes current at a certain, stable frequency, about 2 kHz and 1-2 Amp.
A portable receiver that receives a weak magnetic field with a frequency of 2kHz, and which is selective for that frequency, would be used to find the cable in the walls and the like. It is necessary to find deep-located cables , at a depth of up to 10-20 cm. The receiver will use several bandpass filters in series , the total Q will be above 300-500 and bandwith will be narrow, so frequency stability is important.
The load should consume a sine-shaped current to reduce the number of harmonics , which can complicate the performance of the receiver. Each load harmonics with network harmonics produces additional frequencies, so this should be avoided.
In short, this is the concept

 

I have a system like that!! Made by the "TRIPLET" company, sold as the "Fox and Hounds Live Wire Tracer" system. Except it does not require the load on the line to be drawing any current. It simply sends a high frequency signal down the circuit that it is connected to, and the hand held receiver senses the signal and provides an indication of how close it is by the amplitude of it's sound. One limitation is that in a room illuminated by cheap junk noisy LED lights, there is a lot of other signals present.
So the concept is certainly valid, which is good to know, and the system that sounds quite similar is available.

 

I have a system like that!! Made by the "TRIPLET" company, sold as the "Fox and Hounds Live Wire Tracer" system. Except it does not require the load on the line to be drawing any current. It simply sends a high frequency signal down the circuit that it is connected to, and the hand held receiver senses the signal and provides an indication of how close it is by the amplitude of it's sound. One limitation is that in a room illuminated by cheap junk noisy LED lights, there is a lot of other signals present.
So the concept is certainly valid, which is good to know, and the system that sounds quite similar is available.

Interference is one of the main problems with such a device. In a real power grid, there are a lot of interferences, so some technique must be used to filter them out.And the load must be such that it does not generate even more interference, which I wrote about in post No. 9 . The selectivity of the receiver must be good enough as well.

A few years ago, I had to work with a different device - a faulty cable finder, and if a loaded cable with voltage was nearby, it caused big problems.
This device was designed to find cable deep in the ground, and it worked at about 1khz, but 50hz and its harmonics were very disruptive.