RS232 Break to Toggled relay circuit

[David Wilbourn]

Help Wanted!
Though competent with a soldering iron, I remember just enough electronics
from college to know I would be dangerous designing a circuit myself.....
I need a simple circuit that can monitor the RS232 output from a Palm PDA
for Break signals. When a break is detected a small signal relay will be
toggled. The relay will be used to switch the connection between 2 serial
devices connected to the Palm. It needs to run of 5v.
I have found the ELM626 IC (from www.elmelectronics.com) that detects the
Break signal but I need to convert that to the toggled signal. Can anyone
help me with a simple drawing and component list?

Thanks in advance for any help.
D. Wilbourn

 

[Ken Smith]

Help Wanted!
Though competent with a soldering iron, I remember just enough electronics
from college to know I would be dangerous designing a circuit myself.....
I need a simple circuit that can monitor the RS232 output from a Palm PDA
for Break signals. When a break is detected a small signal relay will be
toggled. The relay will be used to switch the connection between 2 serial
devices connected to the Palm. It needs to run of 5v.
I have found the ELM626 IC (from www.elmelectronics.com) that detects the
Break signal but I need to convert that to the toggled signal. Can anyone
help me with a simple drawing and component list?

I'm not sure I understand what you really want but I'm going to make some
guesses and suggest some circuits. Others are sure to jump in with
improvements.



A break on RS232 usually means "above ground for a long time" I will go
with that and suggest this to detect the break:

+5V +5V
! !
--- 1N914 \
^ / 100K
IN 10K ! 1/4 LM339 \
-----/\/\/\---++----------------!+\ !
! ! >------++---- V1
--- GND----!-/ !
^ 1N914 --- 0.1uF
! ---
GND !
GND

With the components shown, V1 will follow:

5V * (1- exp(-t/(100K*0.1uF)) )

V1 will hit 2.5V if the input stays high for about 7mS. Any time IN goes
below ground, the LM339 will fairly quickly pull its output down to
ground.

1/4 LM339
V1 ----------------!-\
! >------ ?????
+5V ---/\/\/\---+--!+/
10K !
/
\ 10K
/
!
GND

The ????? output will go low when there is a break signal. Now here's
where you can help. Exactly what do you want to have happen when a break
happens. Do you want to make a realy open one time and close the next?

 

[Terry Pinnell]

Help Wanted!
Though competent with a soldering iron, I remember just enough electronics
from college to know I would be dangerous designing a circuit myself.....
I need a simple circuit that can monitor the RS232 output from a Palm PDA
for Break signals. When a break is detected a small signal relay will be
toggled. The relay will be used to switch the connection between 2 serial
devices connected to the Palm. It needs to run of 5v.
I have found the ELM626 IC (from www.elmelectronics.com) that detects the
Break signal but I need to convert that to the toggled signal. Can anyone
help me with a simple drawing and component list?

Thanks in advance for any help.
D. Wilbourn

This should do it:
http://www.terrypin.dial.pipex.com/Images/RelayToggling.gif