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Hi PICsters,

Lots of people have asked for it so here it is, a little analog output
circuit for microcontrollers that covers the common voltage and
current ranges used in instrumentation. Apologies for the hand
drawn circuit.

The input can be, for example, 0-5V analog from a DAC, or direct
from a PWM output pin. The 1uF capacitor filters the PWM
signal to make it smooth DC. With J3 ON the input becomes 1-5V
to produce the offset zero ranges.

The first op amp is the output driver, and its feedback path can
either be voltage (J2 ON) or current (J4 ON). With J1 OFF the op
amp gives a gain of 1, and with J1 ON it gives a gain of 2.

With J4 ON, the second op amp provides current feedback for the
first op amp. It acts as a differential amplifier, using the 100R
resistor as a current sensing element. The 47R resistor does
nothing except fix a linearity problem the circuit had at low outputs.
Two 10k resistors were used in series just because 20k was not
available.

The jumper settings indicate how to select the desired voltage and
current ranges. Hope the ideas in this circuit are helpful to you all.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile: 025 334 069
eMail:  brent.brown@clear.net.nz

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