# One oscillator to toggle between 1/10 Hz and 1 kHz

#### AMIRAAM

Joined Dec 31, 2019
37
Hello everyone

I want to use a Humidity Resistive Sensor that needs AC voltage to prevent polarization of the sensor; the result is converted and rectified to a DC voltage

After research on oscillators used only transistors I find a lot of examples (sincerely I can’t imagine how can you know them all, this is beyond my capacity) and since I am beginner I can’t choose the simplest one that can give me good AC signal

I know “good” and “simple” can’t be together all the time, but I you can the best from simplest oscillators (few components: two or three transistors and three or four moderate capacitors)

A simple oscillator who gives a good AC signal ranges from 30 Hz to 3 kHz

Can I use this simple oscillator to toggle to 1/10 Hz or less to use is for my a timer in the same time as a Humidity Resistive Sensor

Thank you very much and have a good day.

TS

#### Ya’akov

Joined Jan 27, 2019
9,264
What level of accuracy do you need? What level of stability do you need? What level of precision do you need? What output voltage/current do you need?

#### LowQCab

Joined Nov 6, 2012
4,290
We need to know the exact end-result you are trying to achieve,
and if there are any particular Parts, or Voltages, or Functions, that you want.

Any Parts that you specify need to have at least a Specification-Sheet to explain it's operation,
and preferably a Schematic-Diagram.

#### BobTPH

Joined Jun 5, 2013
9,256
Do you need a sine wave or will square wave do?

Why only transistors?

Bob

#### Alec_t

Joined Sep 17, 2013
14,400
A cheap single CD40106 IC contains 6 independent Schmitt inverters, each of which, with one respective resistor and one respective capacitor, could make a square-wave oscillator for those frequencies.

#### AMIRAAM

Joined Dec 31, 2019
37
What level of accuracy do you need? What level of stability do you need? What level of precision do you need? What output voltage/current do you need?
For Humidity: Operating humidity range 40 % to 90% - Accuracy ±10%RH
Since I m not using high Accuracy sensor, I don’t care for the response time or the high Accuracy (Accuracy ±10%RH); Voltage 5V less than 10mA and about 1 kHz (Voltage 1Vrms recommended).
For the low frequency (timer):
Voltage 5V, Current: less than 10mA 0.1 Hz Accuracy ± 1 s

Do you need a sine wave or will square wave do?
For the low frequency (timer): If possible square wave if not this don’t matter
For Humidity: simple sine wave

Why only transistors?
A cheap single CD40106 IC contains 6 independent Schmitt inverters, each of which, with one respective resistor and one respective capacitor, could make a square-wave oscillator for those frequencies.
i saw some examples using o amp but i do not want to use it now.
I'm just beginning , using single cheap or modules don’t help me , I am searching for simple things to understand there logic.
We need to know the exact end-result you are trying to achieve,
and if there are any particular Parts, or Voltages, or Functions, that you want.

Any Parts that you specify need to have at least a Specification-Sheet to explain it's operation,
and preferably a Schematic-Diagram.
i am going step by step, so no big things, a just controlling humidity , temperature ,simple timer....

thanks again

Last edited:

#### BobTPH

Joined Jun 5, 2013
9,256
I do’t see why you would use one oscillator toggling the frequency, two oscillators would be simpler.

For the sine wave, a single transistor phase shift oscillator is as simple as you can get.

Bob

#### AMIRAAM

Joined Dec 31, 2019
37
I do’t see why you would use one oscillator toggling the frequency, two oscillators would be simpler.

For the sine wave, a single transistor phase shift oscillator is as simple as you can get.
I thought that by using one oscillator toggling the frequency it will reduce the number of components compared to two separate oscillators but even if in final using one oscillator have more little or the same number and cost compared to the separates oscillators it will be good.

What I need from the low frequency a small pulse of 1s but the rest of 0.1 Hz it is only for during time to (have 10 s or 20 s only 1s it will be needed for biasing another transistor)

Please even I don’t know if it is possible or no but you can tell me the simplest things

thanks

#### crutschow

Joined Mar 14, 2008
34,826
Do you really need a sinewave?
It's much easier to generate squarewaves.

#### AMIRAAM

Joined Dec 31, 2019
37
Do you really need a sinewave?
It's much easier to generate squarewaves.
i don't know !?
For Humidity sensor: i don’t think that will be deference between square and sine waves because both will be converted and rectified to a DC voltage.

For the timer all what i need from the waves after the during time is small pulse (about 1s or very less)

#### AMIRAAM

Joined Dec 31, 2019
37
Excuse me but I think that my question was not clear, here is schematic for understanding how I imagine this oscillator

The square wave for the timer is represented by the blue color and the sine wave for the sensor is represented by the red color

The Output will be low frequency +5v for 10 seconds and high frequency 1 kHz-1vrms for 10 seconds

For the waves of the timer (blue color) it can be simply logic states (either 5v or 0v)

#### AnalogKid

Joined Aug 1, 2013
11,196
Please post information on the humidity sensor: photo, datasheet, link to info page, etc.

How accurate does the timer signal have to be. You show each half-cycle as 10 seconds. Is that +/-1 second, +/-1 microsecond ... ? What is the timer signal used for?

Does the 1 kHz signal have to be 1000 Hz, or could it be 1024 Hz? Again, what is the required accuracy/precision?

ak

#### AMIRAAM

Joined Dec 31, 2019
37
hello and thanks
Please post information on the humidity sensor: photo, datasheet, link to info page, etc.

How accurate does the timer signal have to be. You show each half-cycle as 10 seconds. Is that +/-1 second, +/-1 microsecond ... ? What is the timer signal used for?

Does the 1 kHz signal have to be 1000 Hz, or could it be 1024 Hz? Again, what is the required accuracy/precision?

ak
Each half-cycle can be as 10 seconds or more , if it is possible the positive state of the timer (blue color) can be less the 10 seconds with a condition to add this deference on the negative state of the timer (blue color) to give the high frequency (red color) more time to operate .
Since is not high accurate timer +/-1 second will be good because some incubators turns eggs each 4 to 6 hours (so +/- 10 minutes don’t matter).
The timer signal is sent to a counter (not really a counter).
for the humidity sensor : I don’t think that the 1 kHz signal has to be 1024 Hz.

#### AMIRAAM

Joined Dec 31, 2019
37
Hello again
Sorry about the retard but I have to do some search
For the sine wave, a single transistor phase shift oscillator is as simple as you can get.
So I decide to do this by the classic phase shift oscillator but when I search for the good configuration I find some additional details like is in figure.
Please what is the deference between them?
Thank you very much