Hello everyone,

This is my first post and i am not an electrical/tronics engineer but rather into another industry.

Problem: How to turn off a simple circuit after a 1 min in the following situation.

I have a water tank which fills up in the morning when we get water from a source everyday. It directly pours into tank and valve is manual. (No pumps etc involved). Problem is overflow.
So I made a simple plastic bottle float and using aluminum foil i managed to create a kind of a float switch. I have a 9V battery connected to a simple 9V buzzer via the float switch.
All is working fine. When tank reaches the level i desire, i get the buzz. Thing is, after i hear the buzz, i manually shut the water valve to avoid overflow. But buzzer won't go off (Level in tank is same) and drains battery and is irritating. As a result now i have an extra job. I open taps and remove some water until buzzer stops. I can use a board and can manage to solder few components.

It should turn off after a minute automatically.(not 60.00 seconds of accuracy..a min or 2 in short is fine - need minimum components). As of now i added a manual switch in series just after the float switch and i simply turn it off. I sometimes forget to turn it on again in evening and next morning never get an alert with water overflowing.

Thank you.

 

If your buzzer needs less than 100mA then this timer module will do the job.
http://www.ebay.co.uk/itm/Programma...hash=item33a6b466ad:m:mrZ2BmvNkMH0HKjmNUZaUug

 

When the float switch is in the off position (low water level), Q1 is in full conduction, keeping Q2 in its off condition. The buzzer is off. When the switch is in closed position, (overflow level), the capacitor C1 charges up through R1, causing Q1 to turn off for a time period, this allows Q2 to turn on in turn the buzzer comes on., After the cap C1 charges up, then Q1 turns back on turning off Q2, and the buzzer turns off. Extra circuitry can be added for discharge of C1 if needed for additional times to use it over again.

 

Extra circuitry can be added for discharge of C1 if needed for additional times to use it over again.

A resistor from the left hand end of C1 to the positive supply will give longer times for smaller values of C1 and will also mean that the circuit is ready for the next operation.

 

I am planning to remove buzzer and add

A resistor from the left hand end of C1 to the positive supply will give longer times for smaller values of C1 and will also mean that the circuit is ready for the next operation.

a 9V relay to do another job for the pump soon.

A resistor from the left hand end of C1 to the positive supply will give longer times for smaller values of C1 and will also mean that the circuit is ready for the next operation.

 

What are the values of R and C and Q (9V transistor battery / DC 9V adapter as power). I will buy them from store and give it a try tomorrow.

 

Hello everyone,

This is my first post and i am not an electrical/tronics engineer but rather into another industry.

Problem: How to turn off a simple circuit after a 1 min in the following situation.

I have a water tank which fills up in the morning when we get water from a source everyday. It directly pours into tank and valve is manual. (No pumps etc involved). Problem is overflow.
So I made a simple plastic bottle float and using aluminum foil i managed to create a kind of a float switch. I have a 9V battery connected to a simple 9V buzzer via the float switch.
All is working fine. When tank reaches the level i desire, i get the buzz. Thing is, after i hear the buzz, i manually shut the water valve to avoid overflow. But buzzer won't go off (Level in tank is same) and drains battery and is irritating. As a result now i have an extra job. I open taps and remove some water until buzzer stops. I can use a board and can manage to solder few components.

It should turn off after a minute automatically.(not 60.00 seconds of accuracy..a min or 2 in short is fine - need minimum components). As of now i added a manual switch in series just after the float switch and i simply turn it off. I sometimes forget to turn it on again in evening and next morning never get an alert with water overflowing.

Thank you.

Why not just put an on / off switch on the buzzer? You have to be there to turn the valve on and off.

 

I built in on a breadboard, using around 9v supply, The buzzer I used was a 1.5 to 3v radio shack type DC buzzer.

R1 is 150K ohms, and R2 is 15K ohms. The transistors are any NPN general purpose transistors. C1 could be in the 3000 uf to 4000 uf range.

I'll explain a little theory on what components to use.

In theory the time costant for the circuit would be (T = R1 x C1) in sec. It only takes around one time constant before Q1 starts conducting again, turning off the buzzer transistor Q2.

But in actuallity after building the circuit I found that due to the low collector resistance R2 with respect to R1, that the time constant is very short, so in order to get a close value for the time duration to keep longer, I rearranged the equation to be used as this (T= R2 x C1), then I was able to get a long delay, before the buzzer turned off.

I took (60 sec. / 15K ohms) which is around 4000 uf capacitor range.

So you can adjust your time delay by using that equation. That way you can work back and forth with the resistor and capacitor value to get a Time delay you would be satisfied with.

The reason for the R1 value being large is to cut down on some of the battery power that will be constantly used up across it.

If you want the circuit to work at the lowest possible current drain possible, then all the resistor and cap. values would need to be recalculated.

As Alberthall mentioned, you will need to put a discharge resistor on the capacitor or else the circuit won't be ready the next time its needed. The value of the resistor needs to be large enough to not have any ill effect on the supply as it will be across the supply when the float switch is closed.

The discharge time of the capacitor would be (Td = C1 x Rd) this is one time constant, so it takes around 5 time constants to have a closely full discharged capacitor.

So you could determine the amount of time it would be to use the circuit again, then choose a TC, that would work for that, then use the equation to determine the resistor value needed.



Hope this helps.