# Possible use of 555 timer

Discussion in 'The Projects Forum' started by trickyrick, May 12, 2016.

1. ### trickyrick Thread Starter New Member

Sep 18, 2013
18
1
I have a dial off an old rotary phone. When I dial a number all the pulses are the same except for the first one. The first one is on for the time it takes your finger to rotate the dial to the finger stop. The rest of the pulses are very quick as the dial returns to its original possition. I need to clean them up some how so there all the same. Was wondering if I could use a 555 timer to do that.
Or some other suggestion
Thanks
Rick

2. ### shortbus AAC Fanatic!

Sep 30, 2009
4,086
1,664
You may be thinking about this 'dial' wrong. It's not the "time" it takes to dial the numbers, it's the number of pulses that are made when the dial returns to the rest position. If they were all the same, there would be no different numbers recorded when you dial. What are you really trying to do?

3. ### crutschow Expert

Mar 14, 2008
13,469
3,356
Does the #1 not put out 1 pulse when you release the dial?

Jul 18, 2013
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The pulse contact is always on or N/C until the dial is rotated and then released, the contacts then OPEN = to the number on the dial.
Contact opens 1 to 10 times = to dial 1 to 0.
Max.

Last edited: May 12, 2016
5. ### trickyrick Thread Starter New Member

Sep 18, 2013
18
1
This is how my dial works
At rest dial is open.
As soon as you start to dial its closed until you reach the finger stop, when the dial starts to return it opens, then it closes and opens very fast according to the number you dialed.
So the first close or pulse is alot longer then all the others. Dialing a 0 the pulse is the longest becasue contacts are closed as soon as you start to dail until you reach the finger stop and let go then you get a series of 9 more very fast pulses.
I need all the pulses to be closer together. Im using the dial as an input to a Arduino board be be used as a score board for a suflboard score counter.

Jul 18, 2013
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That definitely does not conform to the rotary dial standard, or there is a defect, if the first pulse is a result of just moving the dial, then it does not conform to the normal 100ms/ 150Ms between pulses.
Also the standard is an open contact on pulse.
Max.

7. ### trickyrick Thread Starter New Member

Sep 18, 2013
18
1
I have several dials made by Nortel. They hve two sets of contacts on them. The first one is open when dial is at rest when dial is in motion contacts are closed all the time (no pules) until it returns to rest. Second set of contacts are closed at rest and even in motion then pulses when dial returns to rest. So if I wire those two sets of contacts in series thats how I get my situation above.

Jul 18, 2013
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You might this type. Dialing a 4 is four low going pulses, as normal.
The circuit is energized as soon as the rec is picked up.
Max.

9. ### trickyrick Thread Starter New Member

Sep 18, 2013
18
1
Are you saying that i should be looking for the open not the close
(the dial is not with the rest of the phone))

Jul 18, 2013
10,826
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Yes, this would be the normal switching, if the contact initially goes hi you could use a logic gate such as a J-K flip flop etc to detect just the neg or pos going edges?
What is your intended end use?
Max.

Last edited: May 12, 2016
11. ### trickyrick Thread Starter New Member

Sep 18, 2013
18
1
as an input to ardunio
2 dials to 2 input pins on the arduino
there will be 2 sets of 21 output pins controling 2 groups of 21 leds each
so when I dial a 5 the 5th led should light up in one of the groups when I dial 3 then the 8th led will light
Its for a score board for a suffleboard table

Jul 18, 2013
10,826
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I would have thought a small key pad would have been better, I have not used Arduino, I use a pic has capture input where you can select every falling edge which if the Arduino has a similar feature would be an answer.
Either that or detect the first contact closure and after that count the lows or 1 to 0 transitions.
Allowing a total time of around 2sec. would cover the max count time.
By using a pull up resistor on the input to the N/C contact you can make this a o to 1 transition when the contact opens if it switches to gnd.
Max.

Last edited: May 12, 2016
13. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,956
1,131
All you need to do is count the number of times the contacts open. The Arduino should be looking for pulse rising edges.