# Simple On/Off timed circuit

J

#### [email protected]

Jan 1, 1970
0
I am trying to build a circuit that is able to turn a relay on and off
at specified times. I have been working with a 555 timer, and it will
do the job, but I want the circuit to be fully adjustable. I want to
be able to have on and off times of up to 20 seconds, and I want to be
able to have off times longer than on times. Can anyone point me to
the right direction?

C

#### [email protected]

Jan 1, 1970
0
I am trying to build a circuit that is able to turn a relay on and off
at specified times. I have been working with a 555 timer, and it will
do the job, but I want the circuit to be fully adjustable. I want to
be able to have on and off times of up to 20 seconds, and I want to be
able to have off times longer than on times. Can anyone point me to
the right direction?

The 555 timer can be configured so that high time and low time are
each adjusted by their own rheostat (potentiometer). The trick is to
use a diode in parallel with R2. The timing capacitor, C, is now
filled only through R1 and emptied only through R2. Check out the
following excellent explanation.

http://www.doctronics.co.uk/555.htm#more astables

J

#### John Mianowski

Jan 1, 1970
0
I am trying to build a circuit that is able to turn a relay on and off
at specified times. I have been working with a 555 timer, and it will
do the job, but I want the circuit to be fully adjustable. I want to
be able to have on and off times of up to 20 seconds, and I want to be
able to have off times longer than on times. Can anyone point me to
the right direction?

Substitute a potentiometer for a resistor in your 555 circuit.

JM

J

#### [email protected]

Jan 1, 1970
0
The 555 timer can be configured so that high time and low time are
each adjusted by their own rheostat (potentiometer). The trick is to
use a diode in parallel with R2. The timing capacitor, C, is now
filled only through R1 and emptied only through R2. Check out the
following excellent explanation.

http://www.doctronics.co.uk/555.htm#more astables

Thanks! this is what I was missing, two pots and a diode will do the
trick

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