38khz Oscillator problem

[waldopulanco]

Re: Need help about 38khz Oscillator

this screenshot was taken from two different Osc. CD4011 and CD4069, this is 1khz audio modulated to 38khz carrier from CD4066 pin# 2 and pin#3 using Oscilloscope.

The p-p voltage from CD4066 using CD4069 osc is higher than CD4011!!

which is much better CD4011 or CD4069?

CD4011:


CD4069:


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can i use cd4011 or cd4069 as invert like the CD4013 and CD4027, they have non invert and invert!!

example CD4013 then output pin #1 is non inverted and the pin #2 is inverted! how to invert on CD4011 or CD4069?

thanks!!

 

[Audioguru]

Re: Need help about 38khz Oscillator

this screenshot was taken from two different Osc. CD4011 and CD4069, this is 1khz audio modulated to 38khz carrier from CD4066 pin# 2 and pin#3 using Oscilloscope.

The p-p voltage from CD4066 using CD4069 osc is higher than CD4011!!

which is much better CD4011 or CD4069?

A CD4011B has buffered outputs so its outputs switch faster than a CD4069 that does not have buffered outputs.

can i use cd4011 or cd4069 as invert like the CD4013 and CD4027, they have non invert and invert!!
example CD4013 then output pin #1 is non inverted and the pin #2 is inverted! how to invert on CD4011 or CD4069?

A CD4069 has six logic inverters. A CD4011 has four logic inverters if the inputs of a gate are connected together. Use one or use the other one.

 

[betwixt]

Re: Need help about 38khz Oscillator

The levels shouldn't be different though. I suspect some cross-talk between the 38KHz and the output circuits. Mind you, with no filtering that might be expected.

Brian.

 

[waldopulanco]

Re: Need help with 38khz Oscillator

What is your simulator? i am using multisim 13!! i want to share my project stereo coder to help me improve this coder!! i have no experience about designing a ckt!! so im sure is something wrong to my ckt, i want to check it to a professional like you!! i do not want in trouble after i build this! i want to all a filtering because there is harmonic in the output but i dont know how to filter it!! anyone help me?

thanks in advance!!

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@Audioguru i was read your comments here https://www.electro-tech-online.com/threads/another-fm-transmitter-project.117981/page-16

about 222 stereo coder by sir harry! i was email sir harry but until now he does not reply!

 

[betwixt]

Re: Need help with 38khz Oscillator

Thanks for the compliment! - I've been retired for almost 12 years so it's nice I'm still considered professional.

I do not use a simulator except for some digital designs. To be honest, I see them used badly so many times that I have lost confidence in them. I don't mean that to be disrespectful to the software developers, it's just that I see some horrible designs that have been put through a simulator then values adjusted until it 'kind of works' when the underlying problem isn't the values, it's the concept.

What I meant by the levels not being different is that the 38KHz is a logic level signal, essentially 0V and supply line levels, it is there only to open and close the analog switches inside the 4066. It should work equally well whatever the circuit generating the switching signal is, as long as it meets logic levels and has the correct timing. From the stereo encoder point of view, it should make no difference whether it comes from a 4011 based oscllator or a 4069 based one.

What your circuit lacks is filtering on the audio output and on the 19KHz pilot tone. The audio will have some residual high frequencies in it, they are caused by lower frequencies being 'chopped up' by the 38KHz and therefore having sharper edges that they should. The pilot tone is a square wave and that means lots of harmonics. In a better circuit, you would add a low-pass filter in the audio output from the 4066, set to roll off at say 16KHz so it doesn't have much effect on the higher notes in the audio, and, a bandpass or tuned filter in the 19KHz path to remove it's harmonics. Note: you filter both of these individually before adding them at the output point.

Brian.

 

[waldopulanco]

Re: Need help with 38khz Oscillator

thanks!! i am not familiar to those filter mostly in khz range, but in rf 50Mhz to 300Mhz maybe!! what i use to filter the harmonic, LC or RC? I am not try to design a filter in khz range using LC because i dont know how to make a coil in range of mH i am not familiar to ferrite. example according to computation the L value is 15mH what coil can i use it im sure it cannot use aircore coil, but im familiar with air core coil!!

thank you so much for the response!!

 

[Audioguru]

Re: Need help with 38khz Oscillator

An opamp or two and some RC filters can make a sharp lowpass or notch filter.

 

[betwixt]

Re: Need help with 38khz Oscillator

The principles at 300MHz and audio are exactly the same but the components tend to be bigger!

I would follow Audioguru's advice, the filters do not need sharp roll-off because 38KHz is well away from audio frequencies and the first harmonic of the pilot is also well away from 19KHZ. I would suggest you use a quad amplifier (TL074, LM324 or similar), using one amp for the audio filter, one for the pilot filter and one as a summing amplifer at the output. If you want to use the remaining amp in the package you could improve the audio filtering but it probably isn't going to make any audible difference. If you search for op-amp LPF it should turn up hundreds of designs, look for the audio filter being flat to about 16KHz and the pilot flat to about 25KHz.

Brian.

 

[waldopulanco]

Re: Need help with 38khz Oscillator

what value of RC filter in 19khz and the value of rc filter in 38khz?

example
frequency = 19khz
R = 100k
C = 82pf

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this is simulated using LM324!

the Oscilloscope - XSC2 - is the output of 1khz Audio modulated to 38khz carrier!

the Oscilloscope - XSC1 - is the final output of composite stereo with 19khz pilot!

Spectrum Analyzer - XSA1 - ther is harmonic at the range of 57khz with 2mV only, and the 19khz pilot is 70mV out!!



is this a good or bad?:grin:

thanks!!

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can i ask!! i have found 2pcs of CD4001BP on my old electronic kit, can i use it as oscillator for 456khz crystal or resonator?

 

[betwixt]

Re: Need help with 38khz Oscillator

The pilot tone level might be a little too high but that will be ignored by most receivers so it shouldn't be a problem.

Yes, 4011BP will work fine, just connect the two inputs together and it will make an inverter.

Brian.

 

[waldopulanco]

Re: Need help with 38khz Oscillator

Sir betwixt CD4001 not CD4011!!:???::-D thanks!! there is trimmer resistor for the 19khz it can reduce the pilot tone!!

thanks again

 

[betwixt]

Re: Need help with 38khz Oscillator

Oops! my mistake - but the 4001 will work as I stated.

Brian.

 

[waldopulanco]

Re: Need help with 38khz Oscillator

Oops! my mistake - but the 4001 will work as I stated.

Brian.

I will connect the two input pin? how about the other Unuse pin i connect it to ground?

 

[betwixt]

Re: Need help with 38khz Oscillator

Yes, never leave CMOS inputs disconnected, they will 'float' and either pick up signals from other gates in the same package or in some cases thay can let the gate output go into a middle state where both high and low drivers are on at the same time. This usually results in destruction of the gate!

Brian.

 

[waldopulanco]

Re: Need help with 38khz Oscillator

thanks!! how about the ouput of CD4001? is it ok if not connected to ground?

 

[Audioguru]

Re: Need help with 38khz Oscillator

thanks!! how about the ouput of CD4001? is it ok if not connected to ground?

Why would you connect the output of an electronic circuit to ground? To make heat and smoke?
Just think about how much current will be in the output if it tries to go high.

Instead, if you want the output to go low then make the input at a voltage that causes the output to go low.
A CD4001 is a quad two-inputs NOR logic gate. Its datasheet says, "With either or both inputs high then the output goes low". Then if both inputs are low the output will go high.

To make the CD4001 or CD4011 a logic inverter then connect both inputs together.

 

[waldopulanco]

Re: Need help with 38khz Oscillator

can i ask? can i use Inkjet to design a pcb layout or need laser printer? i am using Old way of designing pcb i am using Masking tape and cutter blade to design a layout on pcb.:-D:-D. i have only inkjet printer!!

 

[FvM]

Re: Need help with 38khz Oscillator

I presume you want to use photosensitive PCB subtrate? Should work with coated overhead transparency film (after complete drying). Not so well with transparent paper.

 

[waldopulanco]

Re: Need help with 38khz Oscillator

I presume you want to use photosensitive PCB subtrate? Should work with coated overhead transparency film (after complete drying). Not so well with transparent paper.

i think its better than masking tape! how about the tutorial?