Max038 COsc selector

[merco]

I'm using this schematic
http://www.qsl.net/ari-prato/attivita/generatore/schema.png

but i have a problem with the 4051.

I think the 4051 described above is 4051B, but i have at home only a
SN74LV4051A, so i have to power it only with +5V.

I can't see the correct sine wave signal from max038 output pin when
any output is selected by A0 A1 A2 4051 input pins.

The rest of the schematic works great (i've tried to put a 1uF
capacitor at COsc pin, and i get the max038 working correctly).

What could be the problem ?

thanks

 

[Luhan]

I think the 4051 described above is 4051B, but i have at home only a
SN74LV4051A, so i have to power it only with +5V.

You need to run the 4051 on +/- supplies because the MAX038 does and
outputs a waveform that goes +/-.

Here is how I did mine...

http://members.cox.net/berniekm/maxshemat1.gif

Luhan

 

[Winfield Hill]

merco wrote...

I'm using this schematic
http://www.qsl.net/ari-prato/attivita/generatore/schema.png
but i have a problem with the 4051.

I think the 4051 described above is 4051B, but i have at home
only a SN74LV4051A, so i have to power it only with +5V.

The drawing shows a '4051 running from +/-5V, which most
parts will do. 4051B types can run with Vcc up to 18V, but
they suffer from high Ron when operated at 5V, so a 74hc4051
or other low-voltage type is preferred. It appears 'LV4051
types don't have a -5V Vee pin (pin 7 is ground), we're sorry
to say you can't use one in this application (Philips labels
pins 7 Vee, but always shows it grounded). BTW, I assume you
noticed the schematic doesn't show the 4051's ground, pin 8.

 

[merco]

so i can't use SN74LV4051A....

and what about changing COsc with 4016 or 4066 ?
Some suggestions ?
Probably i can drive "controls" pin with my SN74LV4051A , connect the
4016 outputs to the COsc pin and the inputs to the capacitors
connected to GND...
What about Ron in the 4016 / 4066 ?

 

[Winfield Hill]

merco wrote...

so i can't use SN74LV4051A....

and what about changing COsc with 4016 or 4066 ?

Like the 74LV4051, these parts don't have a grounded
logic supply plus a split analog-switch supply. In
the logic cmos family, only the '4051 '4052 and '4053
switch variants feature that capability. These parts
also allow a wider supply-voltage range than other
low-voltage logic ICs, up to 12 or even 15V rail-to-
rail for the analog supply (i.e. up to +/-7.5 volts).
What's the problem, get one of them. 74hc4051.

 

[JLU_EE]

But I doubt that output capacity or resistance of 4051 maybe have
impact on the accuracy of the capacitor at OCSC pin.
I am not sure.
would you like to give some explanations.
Thank

 

[Chris Jones]

I'm using this schematic
http://www.qsl.net/ari-prato/attivita/generatore/schema.png

but i have a problem with the 4051.

I think the 4051 described above is 4051B, but i have at home only a
SN74LV4051A, so i have to power it only with +5V.

I can't see the correct sine wave signal from max038 output pin when
any output is selected by A0 A1 A2 4051 input pins.

The rest of the schematic works great (i've tried to put a 1uF
capacitor at COsc pin, and i get the max038 working correctly).

What could be the problem ?

thanks

I can't see your schematic, it could be my ISP. Anyway, if you don't need
to use any physically huge capacitors then you could connect one pin of
every capacitor to the Cosc pin, and then connect a switch like a FST3125
so that it will ground the other end of the selected capacitor. If you can
find a chip made from smaller FETs with less capacitance then that might be
even better. The parasitics of any kind of IC switch will affect the
maximum frequency that you can achieve and also will cause some distortion
because the capacitance of semiconductor devices is nonlinear. Of course a
mechanical switch or a relay would give better performance but is more
expensive and bigger.

Chris

 

[joseph2k]

I'm using this schematic
http://www.qsl.net/ari-prato/attivita/generatore/schema.png

but i have a problem with the 4051.

I think the 4051 described above is 4051B, but i have at home only a
SN74LV4051A, so i have to power it only with +5V.

I can't see the correct sine wave signal from max038 output pin when
any output is selected by A0 A1 A2 4051 input pins.

The rest of the schematic works great (i've tried to put a 1uF
capacitor at COsc pin, and i get the max038 working correctly).

What could be the problem ?

thanks

Gotta use a cmos 4051, with the negative supply.

 

[merco]

i have now a cmos 4051. I give it +5 and -5 volt supply.

The problem is that the output waveform is very distorced.
look:
without 4051 : http://i1.tinypic.com/xfvluw.jpg
with 4051 http://i1.tinypic.com/xfvlzr.jpg

is there any way to change this ?

thank you !