How to connect a trimpot as a variable resistor?

[rizla90]

Hello everyone,
these days i have been making this circuit shown below,
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since i dont have a solenoid right now, i am using an LED on pin 3 actually. Today i tried fitting in the variable resistor as shown in the schematic above. Actually i am using a trimpot as a variable resistor but unfortunately no luck! the variable resistor doesn't seem to work as it is supposed to do so! the LED lights up only as if the 1K ohm resistor is connected to it!
here i have posted the pictures as well as a small video showing the problem i am facing. Can anyone please tell me how do i connect this trimpot properly so it acts as a variable resistor! thanks!

here are the pictures and video,

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click on the image below to see the video otherwise click on the link at the bottom,

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thanks,
waiting for replies!

 

[ericgibbs]

hi,
The top pin of the Pot must be connected to one of the other pins.

 

[kubeek]

For starters, do you know how a potentiometer works? So why don´t you take an ohmmeter and find out which terminals are the ends and which is the viper? Then you simply connect one of the ends and the viper, and voila you get variable resistance.

 

[crutschow]

To use a trimpot as a variable resistor you make one connection to one end of the pot and the other connection to the wiper. I can't tell if that's what you did.

 

[KeepItSimpleStupid]

The first pic shows it connected to a short. In terms of the breadboard.

So, you have 3 pins. Put the pot about 75% of it's rotation. Start measuring. Suppose the pot is 1K.
Two pins will show 1K, two will show about 250 and two will show 750.

The 1K is the ends of the pot. The same as a 1K resistor. The wiper will be the common pin to 250 and 750.

It's "customary" in real circuit design that the wiper and an end be connected together when it's used as a two terminal device. This prevents some nasty things that can happen, but it's not required for breadboarding.

Put two wires into your breadboard and connect to an ohmmeter to make sure you understand how the breadboard and pot work. I believe if you did that with the way you have inserted your pot, there would be a short.

One company has now started to make the breadboards transparent.

 

[Jaguarjoe]

Do not forget to add a catch diode across your solenoid when you install it. If this is not done, the back emf from the solenoid when it de-enrgizes will destroy your 555 and LED.
At the moment that the 555 switches, it will consume a lot of current for a very short time. Make sure your 5v power supply can handle that. You may need a capacitor across the 5v supply to help.