Replacement parts...

[LabRat]

I've been rummaging my parts stockpile looking for 1n5239 (9.1v zener diodes),
and found 1n5240 (10v zener diodes).

I'm building up the Simple REN16, and was wonder if people think that this part could be used as a replacement? (Because my mouser order *STILL* hasn't arrived (if not tomorrow, I'm calling to get it tracked)).

[P. Short]

That part is used to limit the voltage on the RS485 chip when you are using RS232 on the link from the PC to the first controller. With a 10V zener the input to the RS485 chip can go to about 11V (10V + 0.7V + tolerance).

[LabRat]

That part is used to limit the voltage on the RS485 chip when you are using RS232 on the link from the PC to the first controller. With a 10V zener the input to the RS485 chip can go to about 11V (10V + 0.7V + tolerance).

So my understanding is that RS232 uses +12v, so with a 10V zener, does this mean that make the "signal" to the RS485 would be in the 0-2v range? (ie. getting close to the "not registering as a valid signal" on the RS485?)

I read the description on how the two diodes were working on the RENs from the Wiki.. and was thoroughly confused about how having those two zener's back to back, was able to accomplish anything.

[P. Short]

In the original design the voltages on the RS485 chip are limited to +9.8 (9.1V for the reverse voltage on the 1N5239 plus the 0.7V forward voltage on the 1N5229) and -5V (4.3V for the reverse voltage on the 1N5229 and 0.7V for the forward voltage on the 1N5238). This, of course, ignores the 5% tolerance on the zener diodes...

If the incoming signal voltage is outside of these limits, the excess voltage is seen across the 1K series resistors.