Propeller Audio Out & Analog In - Circuits & Questions

Cluso99

Referring to the attached circuits...

Audio Out

This circuit has a cutoff frequency of
fo = 1 / ( 2 * PI * R * C )
so, for R1 = 680 ohms and C1 = 10nF the cutoff frequency is 23.4KHz.

Obviously this circuit will only drive headphones or an amplified speaker.

Typically C2 would be an electrolytic of 4.7uF - 10uF.
Would a 1uF mono be suitable???
How is this determined?

Analog In

This circuit uses the Sigma-delta method for analog to digital conversion (see Parallax Semiconductor App Note AN008).

I just though I would include it in my post.

Mike Green

For the Audio Out circuit, C2 would affect the low frequency roll-off of the circuit since, for charging C1, C1 and C2 are in series.

Cluso99

Thanks Mike.

So the low frequency cutoff is approximately...

fo = 1 / ( 2 * pi * R1 * C2 ) since C2 >> C1

So for C2 = 10uF fo = 23 Hz; 4.7uF 50Hz; 3.3uF 70Hz; 2.2uF 106Hz; 1uF 234 Hz;

I can buy 3.3uF and 4.7uF 10V 10% mono X5R in smt 0805.

tdlivings

The low freq corner is
2 /( 2 * pi *( R1+Zin) * C2)

Zin is impedence to ground at pc in your drawing.
50 to 100k say for an amplifier input, depends on the amp.
If it is an op amp circuit where someone wants to keep the resistor
values under 10k for wide bandwidth and low noise then it could be
in the 10K range.

Tom