My XR2206 Function Generator

[Lighty]

Hi All

I'm busy building a function generator using a XR2206 IC, I've downloaded the datasheet for it and a couple circuits off the net and used them to compile my schematic.

However there are a couple areas I would appreciate some help on.

1 - Is the use of the 5k POT connected to SV5 correct, I found it on a circuit off the web stating it would set the offset?, but it doesn't illustrate this in the datasheet, but rather a voltage diver using 2 x 5.1k resistors between +12V and 0V.

2 - Pin9 must have an internal pullup resister, as if left open it defaults to its "high" logic function. To change the function you need to pull it low, so the FSK Sw con would work fine, however, if an external trigger is used, what if the input voltage exceeds 5V? Do I need to use a Zener diode to protect against overvoltage?

3 - As the XR2206 can produce a sawtooth wave if the FSK (pin9) is connected to the sync output, so I've wired it up through the rotary swich so that if its turn to the sawtooth position, it will then do so, and in such a way that one could not sort the sync output to ground if the FSK switch is closed. I've added diodes (D1, D2) to the FSK connection, to prevent any applied voltage (say from a 555) to the EXT FSK trigger from being shorted if the FSK Switch is closed. Is this correct? hope that makes sense!

4 - I'm wanting an offset function (if point 1 indeed doesn't work), would it be best to use an output buffer opamp on the outputs and one could incorporate the offset into this?

5 - Are there any other recommendations that would make this circuit better.

Thanks in advance!

 

[KJ6EAD]

Consider including an output buffer/attenuator system to keep the amplitude reasonably flat across the range of frequencies and wave shapes. You could just use an extra rotary switch deck to change attenuators as you do frequency range/wave shape and combine that with a fixed gain output buffer.

 

[Lighty]

Thanks KJ6EAD,

Not to concerned about the difference in amplitude between waves, but will look into it!

Aslo makes sense to buffer the output to protect the XR2206 against overloading or shorts.

 

[bryan]

I thought the XR2206 was discontinued and no longer available?

 

[Lighty]

I've ordered from a supplier on Ebay so not sure, but there are plenty kits available with the XR2206, so I would image there are some around?

 

[audioguru]

Some people HOARD popular ICs then sell them at a high price when they become obsolete.

 

[dr pepper]

The '2206 is still around, I got a couple recently.
Use a seperate op amp for offset, the offset provided only has a small range.
The sawtooth o/p connects the square wave o/p designed for a pll back to one of the freq i/ps I found it doesnt work that well, but it does work.
This circuit and the '8038 have largely been replaced by the likes of ad9850 dds circuits and similar.
The '2206 does give a good sine o/p.