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Modifying The Design?

R

Ron Hubbard

Jan 1, 1970
0
I found a great circuit for a variable frequency strobe light at
http://sound.westhost.com/project65.htm but I think it could be made a little bit
better by replacing the 555 in the trigger oscillator with an XR2206 wave
generator producing a square wave. The 2206 can be more easily frequency
calibrated than the 555 but the pulse width from the
2206 is by it's very nature, fixed.

If I used the XR2206 would the fixed pulse width cause
any problems?

Ron
 
J

John Popelish

Jan 1, 1970
0
Ron said:
I found a great circuit for a variable frequency strobe light at
http://sound.westhost.com/project65.htm but I think it could be made a little bit
better by replacing the 555 in the trigger oscillator with an XR2206 wave
generator producing a square wave. The 2206 can be more easily frequency
calibrated than the 555 but the pulse width from the
2206 is by it's very nature, fixed.

If I used the XR2206 would the fixed pulse width cause
any problems?

I am not at all sure that duty cycle is your only problem using the
XR2206 as a replacement for the 555 in this circuit. The square wave
output is specified for saturation voltage at only 2 mA, and I don't
see an absolute maximum on the current from this pin.

But, I think you can get other duty cycles than 50% by replacing the
single timing capacitor connected pin 5 to 6 with a pair of unequal
capacitors connected between ground and 5 or 6. This trick works for
the CMOS CD4067, but I can't unravel the schematic of this chip enough
to tell if it will work as well, here. The other tack would be to
have the FSK switch take place at each half cycle, switching timing
resistors for the positive and negative half cycles.

But I don't see your problem with the 555, to begin with. It is
pretty predictable. Do you want a calibrated speed dial on the timing
resistor? I think that the typical adjustable resistor is less
predictable than the 555.
 
R

Ron Hubbard

Jan 1, 1970
0
John Popelish said:
I am not at all sure that duty cycle is your only problem using the
XR2206 as a replacement for the 555 in this circuit. The square wave
output is specified for saturation voltage at only 2 mA, and I don't
see an absolute maximum on the current from this pin.

But, I think you can get other duty cycles than 50% by replacing the
single timing capacitor connected pin 5 to 6 with a pair of unequal
capacitors connected between ground and 5 or 6. This trick works for
the CMOS CD4067, but I can't unravel the schematic of this chip enough
to tell if it will work as well, here. The other tack would be to
have the FSK switch take place at each half cycle, switching timing
resistors for the positive and negative half cycles.

But I don't see your problem with the 555, to begin with. It is
pretty predictable. Do you want a calibrated speed dial on the timing
resistor? I think that the typical adjustable resistor is less
predictable than the 555.

It would be nice to replace the pot on the 555 with a rotary switch and individual
resistors to get certain frequencies. With the XR 2206 the formula is simple and
very accurate;
I can't say that for timing resistors on the 555; it's usually more of pulling out
the multi-meter and doing it by trial
and error.

Ron
 
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