10 second timer

Thread Starter

markosillypig

Joined Jul 21, 2008
188
hi all again i have got this circuit and i want to use it but i have a little problem
i would like it to work for about 5 seconds to 15 seconds can anyone help with the modification required
many thanks
all
 

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Thread Starter

markosillypig

Joined Jul 21, 2008
188
i thought this circuit just fitted the bill
and i dont have a circuit for the ne555 timer that fits the bill
it has to drive a 20amp relay for a duration of 5 to 10 seconds
 

hgmjr

Joined Jan 28, 2005
9,027
It may be that all you need to do is scale the oscillator by a factor 100 to 1. You should be able to do that by using a 0.1uFd capacitor for C3.

hgmjr
 

iONic

Joined Nov 16, 2007
1,662
How is the timer to be triggered, manually when needed, when a input signal from another devices goes logic High/Low?...

Using a 555 R1=100K Pot, C1=200uF will give you from 0 - 22 seconds, aprox.
The output would be high for this time period.
 

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Thread Starter

markosillypig

Joined Jul 21, 2008
188
it wants to be opporeted by a remote push to make switch momentary
then the relay wants to be triggered for aprox 10 seconds or more
 

Thread Starter

markosillypig

Joined Jul 21, 2008
188
How is the timer to be triggered, manually when needed, when a input signal from another devices goes logic High/Low?...

Using a 555 R1=100K Pot, C1=200uF will give you from 0 - 22 seconds, aprox.
The output would be high for this time period.
what is the Q1 ??
a 2n222 or a 2n7000 ??
 

iONic

Joined Nov 16, 2007
1,662
what is the Q1 ??
a 2n222 or a 2n7000 ??
A general purpose NPN, 2N2222, 2N3904...

You will have to choose a relay that meets your 20A contact rating and one that can be triggered at your 555 supply voltage.
The absolute max voltage for the LM555 is +18V.
 
Last edited:

Thread Starter

markosillypig

Joined Jul 21, 2008
188
How is the timer to be triggered, manually when needed, when a input signal from another devices goes logic High/Low?...

Using a 555 R1=100K Pot, C1=200uF will give you from 0 - 22 seconds, aprox.
The output would be high for this time period.
is the 200uf a ceramic or electrolytic as i can not find any ceramic on ebay ?
 

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mik3

Joined Feb 4, 2008
4,843
In the schematic it is not polarized but because you will use an electrolytic one you have to take care of the polarity. Also, you need to put a resistor between the base of the transistor and the output of the 555. Its value depends upon the supply voltage (it should equal the relays coil voltage but be less than 15 volts), the current the relay needs and the gain of the transistor.
 
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