How to trigger a 5 sec delay without using 555 ic

Discussion in 'General Electronics Chat' started by tpny, Oct 15, 2012.

May 6, 2012
216
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I want a pushbutton when pressed and released to trigger a 5 second (or x seconds whatever) voltage level change (high to low or low to high doesn't matter) without using a timer ic. Any guidelines? Thanks!

2. RRITESH KAKKAR Senior Member

Jun 29, 2010
2,823
91
You can use a relay timed by a charged capacitor or in place of relay you can use transistor..

May 6, 2012
216
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Yes, I knew I had to have a cap in there, just didn't know how to put it in a circuit to serve this purpose. Do you have a drawing? Thanks!!

4. crutschow Expert

Mar 14, 2008
21,121
6,010
What voltage(s) do you have for power?

May 6, 2012
216
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between 14~16Vdc

Apr 30, 2011
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You might be able to use a three inverter oscillator and a counter.

7. ScottWang Moderator

Aug 23, 2012
6,553
1,009
You can use two NPN transistors connect them similar as darlington, but the each C of two NPN connecting a 10K to +V.

The circuit as this:
+V → Start Key → 1K → Cap([-] toGND) [+] → 1M Ω → two BJT → C output of second NPN.

The similar as darlington driver on the top of right side of page 2.
Take off the Rbe,Re resistors from the first NPN Tr1.
http://panasonic-denko.co.jp/ac/e_d.../common/catalog/mech_eng_cau_appli.pdf?via=ok

8. crutschow Expert

Mar 14, 2008
21,121
6,010
You could use a single MOSFET which has the advantage of a very high input impedance, allowing a larger value of resistance and a smaller value of capacitance then a BJT.

The circuit would be +V$\rightarrow$Start Key$\rightarrow$capacitor$\rightarrow$MOSFET gate & resistor with resistor$\rightarrow$ground. Connect the MOSFET source to ground and the drain through a resistor to +V (resistor value determined by load). This will cause the MOSFET drain output to go momentarily low and then back high when the Start Key is pressed. Try R = 10MΩ and C = 0.5μF to start.

To reset the capacitor you will need to add a resistor, 1MΩ or less, from the switch output to ground.

9. Dodgydave AAC Fanatic!

Jun 22, 2012
7,723
1,281
The relay will operate immediately the push switch is pressed, and stay operated until the capacitor discharges,time depends on coil resistance and capacitor value, bigger values = longer time delay.

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