Emitter Follower + LPF Sine Convert for CD4060

How approximate? At a fixed spot frequency an integrator followed by a bit of diode shaping to clip the peaks off isn't far off the mark.

Otherwise you would need a very steep low pass filter to get the third harmonic component of a square wave down to acceptable levels.

AAA cells, to produce a reference 16Hz sine wave. Required output is

nent count and cost.

with an RC smoothing filter to do the job?

You can certainly build a two-pole Sallen-Keys filter around an emitter-fol lower.

If you follow an NPN follower with a second PNP follower you can get a four

-pole Sallen-Keys without much DC offset

oscillator, but prefer the option of multiple output frequencies the CD4060 affords.

If you are cleaning up a square wave to something approximating a sine-wave , you are going to want different low pass filters for each output frequenc y.

If you want something that still looks like a sine wave at a range of frequ encies, you need to think about putting your square wave through a - say -

ponent count and cost.

it with an RC smoothing filter to do the job?

ollower.

ur-pole Sallen-Keys without much DC offset

ve, you are going to want different low pass filters for each output freque ncy.

quencies, you need to think about putting your square wave through a - say

- 16 stage shift register, and tacking resistors between each output and a summing junction to make an FIR filter. It gives you a staircase approximat ion sawtooth wave which is easier to filter out, and a single low pass filt er can cover a limited range of output frequency options

Might as well put it all in a 8 pin mcu like an attiny, cost less than an x tal and you can do a proper pwm sine so the filter will be easy

getting 5Vpp from

Hmm is there some other power source? How long are your AAA's going to last at

Not that easy... and keeping up the 5 V ampltude.

Lot's of ideas... all involve more parts. Does the 16 Hz have to be very accurate? (do you need the x-tal reference?)

George H.

At 16Hz, capacitor dissipation factor can make accurate filters difficult. If you can afford the space, use a quad OpAmp and do this...

...Jim Thompson

An RC lowpass filter and an emitter follower might be round-ey enough. Spice it and see.

An HC4060, or a CD4060 and a buffer, might be better if the R in the RC is a low value. CD's are wimpy drivers. If you use a high-beta transistor, like a BCX70K or some such, you might use a 1K resistor and 10 microfarads or so.

Phase shift oscillators are nasty. They either don't oscillate or they distort badly.

You could do an N-path filter with a CD4051, like on page 6 here:

Won't someone please do an N-path filter?!

Cool PDF, but that filter may be overkill for the application. An analog filter, with a cheap r-r opamp, might be the next step up from a single RC.

It may be more expensive than a CD4060 in quantity, though.

yeh but if it doesn't need to be super accurate you can skip the xtal

-Lasse

you could do a 'poor' man's programmed DAC out of multiple outputs, from shift register or up/down counter, then the rquirement on your filter is much less. From memory, your low pass frequency moves out while the amount of required reduction goes down and you quickly end up with better than

One other technique, but forgot what it was for, I think low harmonic content motor drivers, we used to 'cheat' and put a ramp through a squaring ckt, which is fairly close to a sin wave, too.

I had missed the 16Hz (as opposed to 16kHz). D'oh.

One 8-pin (or 6-pin!) micro, one R, one C, some software to generate PWM, and voila! You have a nice clean sine wave.

And one that for all practical purposes painlessly goes to the rails, for that matter.

not at 50mA though, but you can probably find a n+p fet for 10 cents

-Lasse

This is what I had in mind for a fixed frequency. But I cannot find any instructional material on how to do it.

Can you provide a reference or circuit example?

Many thanks,

Martin King

I would like to give this a try too. Can you direct me to an available circuit and code?

Here is a related video, but no details.

Martin King

I have tried this in MultiSim, but can't get the RC filter to work. Whatever I do, it just flat-lines the sim.

Martin King

Do you have LT Spice? I could whip up the sim to get you started.

I never much liked MultiSim. LT Spice is great. And free.

with an Xor gate you can convert the 4060 output into a staircase

another option would be a cheap microcontroller (PIC10?) producing a PWM or "magic" sine followed by a low-pass filter.

Can't you just CALCULATE it ?>:-} ...Jim Thompson