R26 QUESTION

SWAMPFOOT

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ok this is for the geniuses, because i'm not one.
If r26 controls the delay in the test mode and the one thats in it gives about 4 sec delay and increasing the  the value increases the delay can we put in one of those POTS (variable resistors potenometeor something like that) and change back and forth if we choose to do so.  I 'm not real familiar exactly how they work but like a volume control cant you turn up the resistance and thus change the delay time.  Im not sure what kind of range you could get from one of these things or if they can even do that.  Boy it would be nice to solder one in and be able to adjust it to say 4sec--20 secs---30 secs etc.   is it possible to do this?  Just been thinking  about it .  I  guess thats why i been smelling smoke!  Help  from the geniuses is needed here.  
 



Brian

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Yes you can use a pot in the place of the regular resistor.

There are physical limits to the value depending on the circuit.

It is always good practice to put a fixed resistor of some low value say the 4 sec time and then put a pot in line with it and adjust the value from there.  This way if you accidently turn the pot to zero resistance then you will not fry any of the electronics.  555 timers have this problem.
 

bat

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Brian, as you know I have been wanting to try a Varible Resistor on the RS Pir on the R11 Resistor....been too busy trying to find the right part.  Help me out here...given the fact that R11 @ 1800k=30 secs. I know I want to try to acheive this range (6 sec. to 2.9 minutes) This should give me a 360k-10,000k range thereabout, is that correct?  I was going to try a Pot. tonight but I saw that I probably had too small a one to use.  How do you connect the ''fixed'' resistor in relation to the Pot to stop at 4 sec.?  Thanks!
 

Brian

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You should connect the resistor in series like wfontjr says but you will have a hard time finding a pot that goes from 390K to 10M.  I am going to email you a way to get around this without using a pot.  You will have to use jumpers or switches to connect resistors in parallel to achieve the timing.  Most pots are 1M max.  You might find some that go higher but they are single turn and they are hard to set an exact resistance since they move from one resistance to another by just barely adjusting the pot.

I will get it to you today.  Let me know when you get it.

I noticed you don't have an email listed so I can't send it to you.  Email me if you want the drawing on paralleling the resistors.



(Edited by Brian at 7:51 am on Mar. 19, 2002)
 

Brian

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Its on the way.

Keep in mind that there are physical limits to how high you can go on some circuits concerning resistance.  Just because you calculate say 20M for a timing sequence the circuit may not work with this value due to its design.  So you may have to find a happy medium.  I would try the large value first and if it doesn't work back off.



(Edited by Brian at 8:20 am on Mar. 19, 2002)
 

bat

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Bryan, I got the e-mail on now....must have messed up when I fixed all that and checked the private button :surprised-purple:  I sent you an e-mail with it also.  Thanks again.
 

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