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In article <3687@tukki.jyu.fi>, sm@tukki.jyu.fi (Seismo Malm) writes:
:      Can  anybody  help  me with  XR-2240  Timer.  The  pinout  is 
: following
: It was the only timer capable to produce delays of 100 sec 
: availlable from local electronic store and they don't have Exar
: datasheets. I guess, that I should connect pins 8&10 and put timing
: resistor between pins 13&15 and timing capacitor between pins 13&9?
: Triggering is by positive pulse to pin 11? Am I right?

One of my first electronics projects was the XR-2240!  After I found out
that a 555 isn't too good for an 8 hour delay.  See if you can find the
magazine Radio Electronics, July 1978, page 61-65.  It is on the XR2240,
XR2250, and XR2260.  Timing is done with a resister between 16 and 13,
with a cap between 13 and ground.  Trigger is positive pulse to pin 11.
In the examples, they have a 20K resister between 15 and 14, something
about a stable time base.  The output pins are open collector pull up type.
How it works is kinda as follows: you have a 555 oscillator tied to an
8 bit binary counter.  If the oscillator has a cycle time of 1 minute,
output pin 1 will have a cycle time of 1 minute, pin two 2 minutes, pin
three 4 minutes, pin four 8 minutes, up to pin 8, with a cycle time of
128 minutes.  For your delay in minutes, 'or' together the pins you
want to add up to the required delay.  Attach it to a 10K resister that
is tied to V+.  When the output line goes high, then the time delay you
want has occurred.  Notes: if you measure the output voltage, you'll see
that it increases kinda like a binary ladder, so you'll need a threshold
on the output detect circuit (something I overlooked).  Also note that
I last used this beast in 1980, so my memory is foggy at best.  I'm actually
a bit surprised I was able to find the article.  Good luck.

: Thanks.
: Seismo Malm      sm@tukki.jyv.fi 

PS: the sample circuit I have also has a 0.01 microfarad cap between pin
12 and ground.

-- 
Kenneth Ng: Post office: NJIT - CCCC, Newark New Jersey  07102
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