Analog output from BasicStamp? (Replacing an analog pot with control from BS2)

TonyA

Hi,

I am trying to achieve an analog output from the BS2. I 've read that you can simulate analog output using PWM.

Is there a way you can get a resistance output from the BS2?

What I'd like to do is replace an analog potentiometer on a certain device with control by way of the BS2.

Would a digital pot chip come into this? Or a digital to analog chip?

Thanks for any help, I appreciate it.

Tony

Beau Schwabe

There are several application notes on how to do this... My favorite chips for doing this·are the DS1267 (Dual Pot) and the AD8803 (Octal Pot).
Here is an example that I did a few years ago...

http://webpages.charter.net/schwabelove/BasicStamp/

...See:
"AD8803 Octal Digital POT interface"
"DS1267 Dual Digital Resistor Interface"
"Radio Control Electronic Speed Controller using a Stamp1" for code and schematics.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 8/19/2005 7:22:34 PM GMT

TonyA

Hi Beau,

Thanks for your help. Interesting projects there.

If I wanted just one pot control would the ad5220 work for controlling a simple analog oscillator?

(I noticed something on your site that gave me an idea. How could I go about getting a control voltage (CV out) output from the BS2?)

Thanks again,
Tony

Post Edited (TonyA) : 8/19/2005 7:30:40 PM GMT

Beau Schwabe

I think it might help if we knew more of what you were trying to do in order for us to optimize the solution.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

TonyA

Beau,

I want to control a simple oscillator with the BS2. replace the oscillator's analog pot (used to control the oscillator) with control via the BS2.

Thanks,
Tony

Beau Schwabe

What does the schematic of your oscillator look like? If the pot has a common node to power or gnd, then you may not need a digital pot at all.
You might be able to get away with using the PWM command with an OpAmp set as a voltage follower.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

TonyA

Hi,

I am looking into the possibilities of using the BS2 to control very simple oscillators (sound effects). The types of oscillators
you could make from a 555 timer chip and the chip in the attached schematic.

Also, how I might make a simple control voltage output. The type of CV used for analog musical synthesizers/oscillators. (I don't know too much about this stuff, so sorry if I am using the wrong terminology). The CV output would be used so that you could plug into an analog synth and control it.

These are my 2 objectives. I am interested in applications that involve sound manipulation and control. I have already worked somewhat with midi.

Thanks again for your help, I really appreciate anything you can impart to me.

Tony

The attached schem is from a kit available from electronicgoldmine.com *I want to be able to replace the cds cell with controll fron the BS2.

Post Edited (TonyA) : 8/19/2005 7:58:23 PM GMT

Beau Schwabe

Tony said...
how I might make a simple control voltage output

There are a couple of ways... One is to use a DAC (digital to analog converter) IC.
Another is to use the PWM command in combination with an OpAmp configured as
a voltage follower. (See attached schematic)

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

TonyA

Thank you for your help. I will give this a try.

Tony