Sweep generators with a 555 chip?

Hi all,

How easy would it be to build a sweep generator using 555 timer chips or even a 556? The frequency coverage has to be 20khz to 80khz.

I need three, one has to go from 20khz to 80Khz, one has to go from 20khz to

Any ideas for circuit diagrams would be very helpfull when you have the time...

Thanks...

I would use a 8038 or a max038, not a 555. It would be easier to control, but more expensive

martin

After the first death, there is no other. (Dylan Thomas)

Ok Martin,

Where can I find a circuit diagram for a sweep generator based on the 8038 or the MAX038?

Paul..

google ne555 linear ramp or howland current pump

You can use a 555 multivib to drive the howland which again may be more controlable than using a 555 as a linear ramp, but more complicated.

before some suggests it, you dont need a PIC

martin

After the first death, there is no other. (Dylan Thomas)

I meant to say that you drive the howland output into a C which generates a linear ramp. You will need a fet or CMOS analog switch across the C to discharge it at the end of the ramp

martin

After the first death, there is no other. (Dylan Thomas)

Hello Winfield,

That's more than what a six pack of the good stuff costs.

An alternative might be to check out and adapt a VCO design from app notes. National's AN-74 has one in there, built around a quad LM339 (figure 17). That chip is under 50c single qty, or under 20c in large qty. Of course, this doesn't generate a sine wave but then again neither would the 555.

Regards, Joerg

or

the

The XR2206 costs less than $5.00 retail; cheaper at Digi-Key or Mouser, and makes a great [sine] wave sweep generator.

Ron

How about these ideas:

(1) Use a 74HC4046 and a CD4060 or other longish divide by 2 chain.

A binary weighted string of resistors plus a smoothing capacitor can make a fairly good ramp to feed the VCO's input. This gives a linear sweep.

(2) Use the VCO in the above to clock the CD4060 to make a exp() type of ramp.

(3) If you just have to use LM555:

First you need a sweep controlling voltage:

VCC ! / \\ / \\ ! C(large) +----!!------ ! ! / ! \\ ! / ! \\ ! ! +---- V(sweep) +---+---!+\\ ! ! ! ! >-+ --- ! -!-/ ! --- ! ! ! ! ! ------+------ Pins 2,6 ! ! GND -----/\\/\\-- Pin 7

Buffering as shown, means you can use a JFET op-amp to let you use large impedances in the RC circuit.

Next you need a VCO circuit:

R1 GND-/\\/\\--- R2 ! R3 V(sweep) -+--\\/\\/\\-++--/\\/\\-- ! ! ! \\ ! ! / ! ! \\R4 ! ! / --!-\\ ! R8 ! (A) ! >--+-/\\/\\/-+-- Pin 2,6 +--+-/\\/\\-+--!+/ ! ! ! R5 ! ! \\ ! ! ! / Pin7 ----/\\/\\/-------+ R6\\ R7 ! / --- C1 ! --- GND ! GND

If you have a spare op-amp buffer the signal at (A)

R3 = R7

R5 = R1//R2

R4 = R6 and much less than R5 unless you buffer

R1 = 3*R2

This circuit (unless I messed up) makes the 2nd LM555 give you a near

I agree the XR-2206 is an excellent chip for the job, and I also mentioned it. But I suggested one might have to get it from Exar's sales reps, because I couldn't find it at either DigiKey or Mouser. AHAH! Jameco stocks it, $3.29 qty 10, but you have to leave out the dash when searching their site. Donberg also has it,

BTW, the intersil 8038 is still in stock, here:

However, two months ago, it was $4; now, it's $14.90!

Regards, Bob Monsen

Having used them both, I find that I just like the 2206 a whole lot better.

Ron

Since the XR2206 hs been mentioned in subsequent posts, have a look at this