# Automatic On/OFF Timer Circuit Required

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#### mahesh_jo

##### New Member
Dear Friends
I need an automatic On/Off timer circuit to drive a water cooler (220V, 5 Amp). The circuit should have two knobs for setting the on time and another for off time. Setting the on time to say 5 minuites and Off time to 10 minutes should keep the cooler on for 5 minutes and shutdown for 10 minutes. The cycle should loop until we dont disconnect both of them from mains.

Thanks.

#### zachtheterrible

##### Active Member
You can buy a very simple timer just about anywhere that you plug into the wall and then plug the device into it. I'm sure that you can set a 10 minute delay

#### mstechca

##### New Member
A two-transistor astable multivibrator is what you need to search for.

It describes exactly what you want. In fact, you can play with the resistors and capacitors in it to get the time you want.

for 230V, you need powerful transistors. I don't think a tip-31 NPN will work for you.

#### audioguru

##### Well-Known Member
Mstechca,
Transistors work with a DC supply, don't you think his 220V cooler is AC?

Have you ever made an astable multivibrator oscillator with a cycle time of fifteen minutes? Not enough base current for the transistors from the extremely high value of their base/timing resistors. Too much leakage current in the extremely high value timing capacitors.

#### Nigel Goodwin

##### Super Moderator
I've been trying NOT to suggest a PIC, but it would make short work of these requirements!.

#### audioguru

##### Well-Known Member
A couple of CD4541 Cmos oscillator/counter timer IC's will also do it easily. They even have an automatic reset when their power is turned-on.

#### bryan1

Why even bother with a dedicated circuit to control on-off times with 220 volts when at any local store you can pick up a ready made 24 hour on-off timer for about $10. I bought an arlec one for my lead acid battery charger so if I'm working away my wife can safely charge flat batteries. ( you guy's know women can be forgetfull) :wink: #### audioguru ##### Well-Known Member Most Helpful Member bryan1 said: Why even bother with a dedicated circuit to control on-off times with 220 volts when at any local store you can pick up a ready made 24 hour on-off timer for about$10.
Because we like designing and making electronic stuff. Your idea spoils half the fun.
The enjoyment it doesn't spoil is designing and making the variable-frequency high voltage power oscillator it needs to control with pots its on and off times. :lol:

#### pravpa

##### New Member
Dear Friends
I need an automatic On/Off timer circuit to drive a water cooler (220V, 5 Amp). The circuit should have two knobs for setting the on time and another for off time. Setting the on time to say 5 minuites and Off time to 10 minutes should keep the cooler on for 5 minutes and shutdown for 10 minutes. The cycle should loop until we dont disconnect both of them from mains.

Thanks.

Hi Mahesh,

hey I was also looking for the same timer schematic..Do you it with any of the timer which has auto ON or OFF

thnx
Pravpa

#### colin55

##### Well-Known Member
You can buy a timer for $5.00 (two for$10.00 in a pack). Why re-invent the wheel for \$5.00?