How to build a simple time delay circuit?

[happytanker]

Hello, need helps in building a simple time delay circuit or switch.

what I need is a 3-5 sec delay in circuit when the power switch is turn on.
In other words when I turn the switch to on, there will be a 3-5 second delay before the circuit is closed.

Can anyone help? Thank you in advance!

happytanker

 

[LiquidKernel]

This can easily be done using an LM555 timer.

 

[Sebi]

Be more specific.
What do You use as switching element: relay or semiconductor?
If semiconductor, what is the load, AC or DC, inductive or resistive?

 

[Russlk]

The 555 timer will give a delay but the problem is that the output is low until the start switch closes then the output goes high for the delay time and goes low at the end of the delay time. The solution is to use a flip-flop that changes state on the falling edge of the clock. In this circuit, the output goes high 4 seconds after the start switch is closed.

 

[k7elp60]

simple time delay

Another approach would to use a N channel power MOSFET. An electrolytic capacitor + terminal to gate. - terminal to source. A resistor from gate to Vcc. Relay in Drain lead to Vcc. With a 1 meg resistor and
a 10uf capacitor the time to turn on the mosfet with Vcc of 12 volts will be
about 5 seconds. Of course the source and the - of the capacitor are connected to the 12 volt - terminal. The relay will energize when the mosfet turns on. The contact rating can be selected for the load requirements. The coil of the relay is 12VDC.

 

[ljcox]

The simplest solution I know of is to use a CMOS Schmitt Trigger such as the 74C14, 40106, etc.

Connect a capacitor from the input to gnd and a resistor from the same input to Vcc.

When the power is applied, the capacitor is discharged and starts charging.

When the capacitor voltage reaches the threshold voltage, the output of the Schmitt goes low.

The delay will be about one time constant. So for a 3 s delay, use say a 10M resistor and a 330 nF capacitor.

Len