no reading

That's because you're the first person to try the Mighty Ohm counter via serial mode and report that it doesn't work... I looked into the serial data format
http://mightyohm.com/blog/2012/02/tutorial-geiger-counter-data-logging/
and its the extra information contained on each line that is confusing things. RadLog just expects the CPM number to be sent, without the other stuff.
Compatibility with MightyOhm serial data will have to be added to RadLog v0.42

In the meantime, you can use the pulse output of the counter into the line in or mic in audio input of your computer and put RadLog into audio mode.

Ok, there will be two reasons the audio pulse isn't counted - either the amplitude or the pulse width is too small.

0. Stop RadLog. put into audio mode and set the input device. Click Start.
1. Untick Zoom into last pulse
2. Untick Trigger plot on detect. The envelope graph should now be continuously updating.
3. Adjust input volume on line in or mic so that the pulses are seen on the display and the peak amplitude of the pulse is much greater than the detect threshold and background noise is below the detect threshold.
4. Adjust the minimum pulse width to, say 0.1ms. The default setting of 5ms is very wide, that just happens to suit the wide audio pulse width of one of my simple Geiger counters.
5. RadLog should now be picking up pulses. Tick trigger plot on detect and Zoom into last pulse.
6. Adjust the minimum pulse width and dead time to suit the shape of your pulse
7. Readjust the input volume and the detect level to provide immunity from counting other noise sources, e.g. lights and electrical motor interference.

If the pulses are still not picked up, please record an mp3 and upload it to the forum. I can then feed it into RadLog here and see what has gone wrong.

I've just had a thought - there is some filtering being applied to the input waveform to obtain the envelope. If your audio pulses are too fast, they may not appear on the envelope plot. If you can clearly hear the clicks when recording, but not see them on the graph in radlog and can only see background noise then this could be the problem. It would be great if you could give me some further information so I can solve the problem.

Note to self: -Add user adjustments to audio filtering