There is a terrible lot of confusion about CV and expression pedals, because different manufacturers mean different things by the same names.
A "CV" input SHOULD mean, control voltage, and you would hope that it just means, put a varying voltage here (eg from a pot across a battery, or from a LFO in an analog synth).
BUT, not always so!! Sometimes it means, connect a tip/ring/sleeve plug here & go to a pot in a rocker pedal, so the unit being controlled sends out (say) 10V and the pot in the rockler pedal sends back 0 to 10.
OR, it could be that you have a mono plug connecting, and the pot is wired as a varying resistor.
Ray's one is expecting a genuine voltage.
I expect a 9v battey across a pot (anywhere from 10K to a 100K pot), preferably linear pot, would do fine.
Just run the voltage from the wiper arm. If the pedal seems to go the 'wrong way', reverse the battery.
To vary range, chang ethe resistor on ray's filter where the CV goes in.