# help in time interval cutout circuit

Discussion in 'The Projects Forum' started by amankarwasra, Aug 1, 2010.

1. ### amankarwasra Thread Starter New Member

Jul 30, 2010
3
0

i need help in makking a circuit which:

run a 1 HP water moter for 2 mins and then stop water moter and run 8 fans for 10 mins................and thus making a loop of------------- water moter 2 min--------------fans 10 mins ---------water motor 2 mins--------- fans 10 mins --------and on and on

but they both can't be on at a given piont of timeonly any one of them

2. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,575
230
I think this should do what you want. The fan and pump motor can never be on at the same time. Since there in interaction between the two time adjustments, set R3 first for 600 sec (10 Min) and then R2 for 120 sec (2 min). The 12V supply can be a 120VAC to 12VDC/500mA "regulated" wall wart or equivalent.

ken

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3. ### amankarwasra Thread Starter New Member

Jul 30, 2010
3
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hi how do you set R3 and R2 and do we need a 12V battery extra for it or we connect the 12 to the main wires actually am all new to this so please explain in details and yes thanks for your time dear

are there 2 transistors and what is regulated wall wart

Last edited: Aug 1, 2010
4. ### tom66 Senior Member

May 9, 2009
2,613
214
@OP: A regulated wall wart supplies a fairly constant DC voltage. You can pick them up for a few dollars, or use a spare one you have. It must be DC, and it should be regulated. You could also use a car battery, but it would be overkill.

The schematic shows R2 and R3 as potentiometers, i.e. adjustable voltage dividers or a pair of complementary variable resistors. These adjust the on/off time, by turning the pots (potentiometers) you can get your desired settings. You MUST use a CMOS 555 with this (such as the LMC555 as spec'd), you cannot use any other type, because the resistors are too large for another type.

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5. ### amankarwasra Thread Starter New Member

Jul 30, 2010
3
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but when i am using it with all AC equipments do i need the car battery etc. and actually i meant by setting potentiometer that do we have to just guess by turning the know or they come with any marking like our fan regulators

6. ### tom66 Senior Member

May 9, 2009
2,613
214
There's a formula for it.

The on time of any 555 astable is, in seconds:

$t_{on} = 0.693 \times (R_1 + R_2) \times C$

The off time is:

$t_{off} = 0.693 \times R_2 \times C$

And from these the frequency in Hz is:

$f = \frac{1}{t_{on}+t_{off}}$

You can measure the resistance with an ohmmeter and capacitance is usually printed on the side of a capacitor, or in this case is specified in the schematic. Remember to normalize all your values, i.e. 470 µF becomes 0.00047 and 1Mohm becomes 1,000,000.

And yes, the circuit posted will need a DC supply, you cannot run it off AC, you will damage the 555 timer. Since it's a CMOS timer, the current consumption is very low, you only need to know about the relay current, which should be no more than about 200mA.

7. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,575
230
R2 in tom's calculations is R2+R3 on my schematic, and R1 is R1+R2 on the schematic.
The nominal values for 2 minutes and 10 minutes are R1+R2=1.5M and R2+R3=390K.
Once you've set those resistances with an Ohmmeter, tweak R3 first to get the 2 minutes and then R2 to get 10 minutes.

This is a handy calculator to get the values and timing: url]http://home.cogeco.ca/~rpaisley4/LM555.html#3[/url]

Ken