This is what I've found.

seems that I really need to build a Scope or logic probe. Do you have a recommendation / link for that?

 

This is what I've found.

seems that I really need to build a Scope or logic probe. Do you have a recommendation / link for that?

Build a scope! Now that's a very ambitious project but it's about as unrealistic as building your very own space ship.

The Piezo element won't tell us much but if there is activity on the TXD pin you should be able to hear buzzing when connected between GND and the TXD pin when data on the displays change..

One of our senior members posted his Logic Probe design, that used a 7 segment LED display but I don't remember who.... I'm OLD!

 

I did a search and found many simple USB Oscilloscopes to build. therefore I sounded about building a one.

you mean probably this: http://forum.allaboutcircuits.com/showthread.php?t=22078

anyway, I have ordered a Siemens Logic Probe as I don't want to waste more time and also concentrate myself on Reflow Station instead of building other devices and spend time in debugging them.

I will inform you as soon as I have the logic probe.

many thanks.

 

Yes, Bertus!

Edit: I have no idea why I posted this or what it refers to, since I don't see Bertus anywhere in this thread. Sometimes I'm answering multiple topics simultaneously, so my guess is that this was a senior moment.

 

Attached is an Opto-Isolator circuit that should switch those two points to ground. No power is needed and it provides a high degree of isolation between the PC and your Reflow station.

is it possible to combine this circuit with a temperature measurement circuit like PT1000 to receive temp. information from RS232 and send the switch commands to this Opto-Isolator?

 

The resulting output (analog) from the PT1000 would have to be fed to an ADC input of a uC. The uC would then convert the values to serial data and send it to the PC.