555 square pulse: Adjust Freq and Duty independently?

I am in the process of building several test equipment devices as it is a lot more convenient to work on projects at home, as opposed to running to the lab every time I need something: psu, function gen, etc...

I am on the function generator and have downgraded to a square pulse generator as I have yet to find any of the available chips I have researched that I thought would be great: MAX038 - discontinued, xr2206 - rare (well, I found it but they are in Australia), and the irl8308 (NTE864) but the chip is $50.00. Also, the square wave pulse is absolutely crucial for uC's, and I really don't need the other wave forms.

My minimum requirements for the square pulse generator are:
1. Adj. Frequency: 1Hz to 10Khz (1Mhz would be great though)*
2. Adj. Duty Cycle *
3. Adj. Amplitude
(*with the Freq. and Duty independent, and also where the problem lies with simple 555's, I think)


SO I was wondering, is it possible to adj. both the frequency and duty on a 555 timer? If so, will one affect the other? It was my understanding that when using a simple 555 for this idea, if I adj. the frequency, it would affect the duty?


Do you think I can accomplish my goal with this circuit?
square wave gen

Otherwise I guess I will just figure out how to make an adjustable square wave pulse generator using an MSP4302012.

Any ideas? Any other function generator chips like the MAX038, or especially the XR2206, that you know of would be great.

hi Phil,

This image is part of a circuit I use for the variable mark/space 555.

Vary the pots values and Ct to suit your freq/mark ranges.

EDIT: added the timing equations image.

PhillDubya said:

I am on the function generator and have downgraded to a square pulse generator as I have yet to find any of the available chips I have researched that I thought would be great: MAX038 - discontinued, xr2206 -

Click to expand...

I have 2ea of the XR2206 new IC's in my stock. Send me a PM if you would like to purchase them for a reasonable amount.

k7elp60 said:

I have 2ea of the XR2206 new IC's in my stock. Send me a PM if you would like to purchase them for a reasonable amount.

Click to expand...

Actually I just found 2 at Mouser.com thanks a lot for the offer though.

Thanks guys for the help, I think I will just order the XR2206 and go with that.

The XR2206 should be a lot more stable and accurate than a 555 correct? Or, if I am just using this for general testing and uContoller stuff, do you think that the 555 timer circuit will do just fine?

However, the 555 timer doesn't actually produce TTL square waves does it?

PhillDubya said:

However, the 555 timer doesn't actually produce TTL square waves does it?

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hi,
The 555 can produce quite good square waves at TTL levels if required.

BTW: if you wanted to have the frequency control independent from the mark/space ratio control, use two 555's or a dual.

The 1st 555 as the astable with its output triggering the 2nd 555 as a monostable.

PhillDubya said:

xr2206 - rare (well, I found it but they are in Australia)

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XR2206 rare? I don't think so: Jameco Electronics, $3.59 ea, in stock.

Jameco Electronics ICs & Semiconductors: EXAR CORPORATION : XR2206

saturn1bguy said:

XR2206 rare? I don't think so: Jameco Electronics, $3.59 ea, in stock.

Jameco Electronics ICs & Semiconductors: EXAR CORPORATION : XR2206

Click to expand...

me said:

Actually I just found 2 at Mouser.com thanks a lot for the offer though.

Thanks guys for the help, I think I will just order the XR2206 and go with that.

Click to expand...

Resolved, earlier...read post........

PhillDubya said:

Resolved, earlier...read post........

Click to expand...

Resolved better, read price....

saturn1bguy said:

Resolved better, read price....

Click to expand...

Lol...

You got me there, Saturn1b. Nice find.

The XR part is the way to go. Real versatile. I am a big XR fan. Makes a perfect function gen at a low low price. Add a Pic to it and you have a nice piece of gear.