# Timer Circuit Problem

Discussion in 'The Projects Forum' started by kauffjd3, May 3, 2009.

1. ### kauffjd3 Thread Starter Member

May 3, 2009
15
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First off hello all! I'm a computer programmer and am new to electrical circuit board development. I have been searching google and playing around with a bread board for a few days now and need some help.

Project:
Temperature driven motor

Example:
Set temperature to 60 degrees

1. If temperature is below 60 degrees run the motor clockwise for 1 second.

2. If the temperature is above 60 degrees run the motor counter clockwise for 1 second.

I didn't do anything with the temperature yet because I may just order a kit.

Anyway I currently have a 556 timer ic setup i monostable mode like this (this is for either clockwise or counter clockwise then the second time will be for the opposite direction):
http://www.eleinmec.com/figures/004_02.gif

I plugged in a 12v blue bulb to the output and hooked up a 9v battery to test it. Nothing happened but then I realized I needed to trigger it.

So I gave the trigger wire 9v power and nothing. So I grounded it and to my surprise it worked. When I quickly touched the trigger wire to the ground and removed it the blue light would stay on for a split second after I ungrounded the trigger wire. Hence the 1 second.

Finally my question:
My temperature kit is going to power all the time so how am I suppose to hook it up to my trigger? Currently if I keep the trigger wire grounded the light stays on.

Thanks in advance for all your help! And if there is an easier way of doing this I am all ears.

Justin

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Where are the specifications of the kit?

May 3, 2009
15
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4. ### mik3 Senior Member

Feb 4, 2008
4,846
63
First note that the kit is not able to measure 60 degrees celcious (5-30).

If you hold the trigger of the 555 always pressed then the 555 will re-trigger and the output will be always high. You need to depress the trigger switch before the timing cycle ends.

To solve the problem replace the trigger switch with a 100nF capacitor and a 10K resistor in parallel with it and use the output relay of the kit to power the whole 555.

5. ### kauffjd3 Thread Starter Member

May 3, 2009
15
0
60 degrees F.

So I removed the battery from the 555 and hook the output of the kit into where I removed the battery? What do I use to trigger the timer?

6. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Leave the battery which powers the 555 and use the relay output of the kit to switch the 555 on/off. To trigger it replace the trigger push button with a 100nF capacitor in parallel with a 10K resistor.

7. ### kauffjd3 Thread Starter Member

May 3, 2009
15
0
thanks for your help Mik3. I'm still confused.

If I run a 100nF capacitor and a 10k resistor from pin 2 on the 555 where does the other end go? ground?

When you say use the relay to switch the 555 on/off where do I feed it if I leave the battery?

Sorry I'm such a newbie. I can program all day but I have a lot more learning to do for this stuff.

8. ### mik3 Senior Member

Feb 4, 2008
4,846
63
The other end goes to ground.

Connect the relay common (C) and normally open (NO) between the batteries positive and pin 8 of the 555.

9. ### kauffjd3 Thread Starter Member

May 3, 2009
15
0
for the time being since i dont have the thermostat kit, I added one end of a 10k resistor to pin 2. Then the other end into a blank spot in the bread board. Hooked the 100nF capacitor from the end of the resistor and the other end to ground. When I give it power the blue light just stays on. Did I do something wrong?

10. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Connect the capacitor between pin 2 and ground, connect a 10K resistor between pin 2 and Vcc (positive supply) and finally connect another 10K resistor between pin 2 and ground.

11. ### kauffjd3 Thread Starter Member

May 3, 2009
15
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with them all hooked the blue light doesn't turn on. removed the resistor from pin 2 to the powersupply and the blue light just stays on again.

12. ### kauffjd3 Thread Starter Member

May 3, 2009
15
0
double post

Last edited: May 3, 2009
13. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Use a bigger capacitor, like 10 uF.

14. ### kauffjd3 Thread Starter Member

May 3, 2009
15
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I don't have anything that big here at the house. I will pick some up and give them a try. Thanks for all the help Mik3! Can you explain what this is actually doing or trying to do so I understand?

Thanks again!

15. ### mik3 Senior Member

Feb 4, 2008
4,846
63
The capacitor will be uncharged. When you power the 555 pin 2 will see 0V and will trigger the 555. After a few ms the voltage across the capacitor will rise at Vcc/2 (pin 2 will be at the same voltage too) and the 555 will not trigger again.

Try more than one capacitor in parallel for now to see if it works.

16. ### kauffjd3 Thread Starter Member

May 3, 2009
15
0
I have 2 .1uF capacitors 1 10k resistor going from pin 2 to ground. And 1 10k resistor going from pin 2 to power source. The blue light doesn't come on.

When I remove the 10k resistor from pin 2 to power source the light comes back on but stays on...

17. ### kauffjd3 Thread Starter Member

May 3, 2009
15
0
just hooked up a 1uF capacitor from pin 2 to ground also same thing light just stays on.

18. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Do you have a resistor from Vcc (positive supply line) to pin 2?

What is the voltage on pin 2 after 1 sec?

19. ### kauffjd3 Thread Starter Member

May 3, 2009
15
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Yeah I have the resistor from pin 2 to positive. Looks like 9.3v at pin 2 when I hook the battery up.

May 3, 2009
15
0