Max038 COsc selector

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

Here is how I did mine...

Luhan

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.

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 Thanks,
    - Win

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 ?

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.

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 Thanks,
    - Win

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

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

Gotta use a cmos 4051, with the negative supply.

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JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.  
--Schiller

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 :

with 4051

is there any way to change this ?

thank you !