PLUS+1 Hardware > I/O Modules

Analog Output

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paterianus:
I need a 0-5VDC analog output.  It appears that the only way to do this is to put a load resistor accross a PWM output.  Has anyone done this and how did you configure it?  Do I need a filtering capacitor?

240glt:
Hi. I did this on a MC090-010, with a PWM output (c1p29).
PinConfig: 3
DitherAmp: 0
ReqFreq:1000

A made a low-pass filter, with two zener diodes (for safety).
I controlled a charger, with a 0-5V input to control the charging current. In my case, I didn't need to change the signal fast. I was more interested in having a smooth voltage. I made a small PCB with three connectors (there are two chargers to control).

The first resistor and zener diode limits the PWM signal to 5,6V peak. Then we have a lowpass filter, with a cutoff frequency of 16Hz. After that a zener diode again, to limit the maximum voltage to 5,1V. I did this for a few years ago, so I don't remember if the output are linear. If you want to try it, you have to do some tests to see if it is smooth enough, if the response to a changing voltage are quick enough, and to see how a certain PWM dutycycle corresponds to a certain voltage.

paterianus:
Thanks, I'll give this a try.  It looks exactly like what I'm looking for.

jsaluk:
I have used a simple PWM output.  I compared 5 vdc to the supply power to establish the max PWM % and then the command was a percentage of that maximum.  I used an MFOut with 4000 Hz frequency.  The valve being controlled seemed quite happy with this command. 

jhorn22:
I need a much quicker response so I just tweaked the RC time constant, but I have another question.  In the IOX012-010 short data sheet it says under the PWM output section "Analog voltage: open loop PWM at 4000 Hz."  Is that just saying that I should set my PWM to 4k and use an RC filter or is there another way to filter this better?

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