[Paul Horwood]

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
40khz and the other has to work the opposit way to give 80khz to 20khz.

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

Thanks...

 

[martin griffith]

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
40khz and the other has to work the opposit way to give 80khz to 20khz.

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)

 

[Paul Horwood]

Ok Martin,

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

Paul..

 

[Winfield Hill]

martin griffith wrote...

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

Good advice. Intersil's ICL8038 was a great chip, but sadly it
was discontinued recently. The MAX038 is a low-voltage power hog
by comparison, so it's nice to see Exar still makes the 2nd-source
XR-8038A, see http://www.exar.com/product.php?ProdNumber=XR8038A
Mouser has the NTE864 renamed part in stock for $7.58 each.

Exar's XR-2206 is another nice audio oscillator chip to consider.
http://www.exar.com/product.php?ProdNumber=XR2206 Available
from Exar's reps, http://www.exar.com/page.php?contentID=5

 

[martin griffith]

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)

 

[martin griffith]

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

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)

 

[Joerg]

Hello Winfield,

Good advice. Intersil's ICL8038 was a great chip, but sadly it
was discontinued recently. The MAX038 is a low-voltage power hog
by comparison, so it's nice to see Exar still makes the 2nd-source
XR-8038A, see http://www.exar.com/product.php?ProdNumber=XR8038A
Mouser has the NTE864 renamed part in stock for $7.58 each.

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

 

[Ken Smith]

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
40khz and the other has to work the opposit way to give 80khz to 20khz.

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

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
50:50 square wave output

 

[Ron Hubbard]

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
40khz and the other has to work the opposit way to give 80khz to 20khz.

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

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

Ron

 

[Winfield Hill]

Ron Hubbard wrote...

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

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, http://www.donberg.ie/index.html

 

[Bob Monsen]

Ron Hubbard wrote...

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

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, http://www.donberg.ie/index.html

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

http://www.futurlec.com/ICHarris.shtml

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

Regards,
Bob Monsen

 

[Ron Hubbard]

Ron Hubbard wrote...

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

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, http://www.donberg.ie/index.html

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

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

Ron

 

[dB]

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
40khz and the other has to work the opposit way to give 80khz to 20khz.

Since the XR2206 hs been mentioned in subsequent posts, have a look at this
http://www.davidbridgen.com/swpgen.htm