The DS1802 is the dual audio 45kOhm (typically) pot with 65 steps
(64x1dB and mute), known around for its possibility to be controlled by
its own pushbuttons instead of, usually needed, certain logic circuitry.
It is available in DIP package and hence seems very appealing for DIY.
Most of the digital potentiometers (there are exceptions like WM8816 and
X9312) can not accept signals much beyond their supply voltages. For
DS1802, 0.5V below the potential at its Gnd pin is the bottom, and 0.5V
above the Vcc (whose safe maximum is 5.5V above the Gnd pin) is the
upper limit. There are a few ways to center the signal inside these
boundaries and Dallas recommends Wheatstone Bridge circuit (see App Note
161). I decided to shift the supply rather than signal, thus with one
more regulator I could keep the signal path clean. So, DS1802’s Gnd pin
went down to -2.5V and all the other pins of DS that normally should go
to ground went to this pin: Agnd, Zero-Crossing (enabled) and Mode
(stereo), as well as the Up/Down buttons. Resistive networks themselves
are connected straightforward. The DS1802’s pin layout appeared almost
ideal for such application.
Post a Comment