From the digital designer’s perspective, it’s unfortunate that the real world is ana-
log. While many low-cost microprocessors (uP) have A/D (Analog-to-Digital)
inputs, I am not aware of any common and inexpensive uPs that have real D/A
(Digital-to-Analog) outputs, although the Microchip PIC 1400 does have two crude
4-5 bit analog outputs. Naturally, this shortcoming is sorely missed when creating
any type of analog control application, as well as many other applications.
There are two different means of simply and easily generating quality analog sig-
nals from digital signals. One method generates DC and low frequency (a few Hz)
analog outputs. The other creates AC signals into the high audio-frequency range.
Both methods can provide up to 10 or more bits of resolution and noise that’s 60 dB
or more below full-scale. The DC/low frequency approach uses two capacitors, two
resistors, and a diode. The high-frequency circuit requires only two resistors and two
capacitors.
It’s important to note that the circuits provided are basic approaches. You can
experiment and modify them for your own application. In addition, these procedures
can employ circuits that can be changed dynamically by the uP, as required.
