555 used as a delayed pulse generator?

Aug 23, 2005 10 Replies

I'm looking to set us a simple way to turn something on after 10 seconds. The resulting output after the end of the 10 seconds needs to be a momentary pulse and not stay in a closed position.


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Like this.



Circuit is started with a momentary contact switch. After 10 seconds (exact time isn't critical here +, - a second or two is fine) the circuit momentarily outputs a pulse. I thought I'd feed the pulse into a switching transistor to make it operate as a momentary contact switch.


Thanks in advance!



Lawrence



time

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Here's one that gives about 1 second delay, 1 second pulse. Could also use one 556 instead of 2 555s. Delay/pulse is 1.1RC where R is the 22K resistors and C is the 47 uF capacitors. "Sic hoc legere scis nimium eruditionis habes." (If you can read this, you're overeducated.)

begin 644 555delayed pulse.gif M1TE&.#=A5`+7`-,`````````J@"J``"JJJH``*H`JJI5`*JJJE555555_U7_ M557___]55?]5____5?___RP`````5`+7``,$__#)2:N]..O-N_]@*(YD:9YH MJJYLZ[YP+,]T;=]XKN]\\[__`H'!(+!J/R*1RR6PZG]"H=$JM6J_8K';+[7J_ MX+!X3"Z;S^BT>LUNN]_PN'Q.K]OO^+Q^S^_[_Q8`&`"$A"F"$H6&%X@/C12+ M@)*3E$F/C)HJ!)T$S8H+F;NWTQ,^AX6W(9R[]Q:6? MFX(J"NF%2&T&4#K)-$6I4U>.%I6D@#(:!J?'G(-C9'5F6.:2(1X92*A8#M3% M2E\\"(R"NN)AI9&M[7=?EJX5>6JJ&3+5"H*N^WH*I_UZ(6L5LL^L$BEDFN5J& MK9)5N$.ML9UXBTZ!+\\C?#$-80Q_>$'PT+"+3=JBZH,"0#$*,6A(+N(1]I,*&(C0A$YEP MNQ__QK"!2#PA#YU@1>4%P8*U6B$9C70?T_4816/",=U97&):FPB"MMX MJC>F\\(I*W*,+P[B_.W*KA%QD8Q"_^$(I$E&.04,D#F5H2/+APC$BUL/P#;;WA1FEY;OMBOS)`Q9HVG5S0F.`Z;:Q9-;VR% MWOZ5MV0C+#-^>Z8C(WC'?.!PX91L"^&N&(%.AFT^AGS:*4(VN_6]LGS42Q!= M&,+*R$WQ"*-T-:4]&7U#-C.1,6Q.RK!Y:I$-LU,I2MXQ)YAOV-+?>/J2(^X?9S:6 M8Z;SC0/4F6`%]]77^EV^4U[,?R_-6WPZ/GF6]_)Y$4];S$=0\\XV?`]'L MWJUE^W;TN4[\\W)4UD(Y1&`ZK7WOK66SXK/M3MXJ_/*PS_/E@3U[TT;@2K[G= M]];FO?B&"_U##T]Z\\[K=ZT#VO+-'IUF#/,GUZK4ON[J_ONGFCZ[;V6V' MW'/>$K`8Y_>[SR0N+R[2VEW_\\9'^_/]_G>W^9)=_[?=_,X-_M95W+O5UQ'`2EA] M[(1H.E&8F9U\\N%Z':A\\7PB#FB*'/EATQK9AOT)B'&B\\+#&C-%H'1$B)[/@6)0>@.XI1/=3/&>)VFD#(BD.-EZ2DJD4!JE>/D&)5H153JA4IJE6KJE7-JE7OJE8!JF J8CJF9%JF9GJF:)JF:KJF;-JF;OJF)JGDA`!```[ ` end

time

This does what I think you want:

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Terry Pinnell Hobbyist, West Sussex, UK

This looks easy Terry, I tried Johns circuit on a breadboard last night. I'll give this a try too.

Thanks, Lawrence

BTW, nice website you have there.

pulse

time

pulse

That's what my circuit does.

Terry Pinnell Hobbyist, West Sussex, UK

Hi Terry, It's probably me but I couldn't get it to work, I used a pnp 2N3906. I tried various combinations of caps and resistors but no luck.

Any ideas?

In

Without more information, not really. Best guess would be that you've made a wiring error. As you see from the simulation - the circuit does what it's supposed to do.

How are you testing it? 'Scope, DMM...?

Is the mono working? If not, then obviously the brief pulse won't be generated.

Terry Pinnell Hobbyist, West Sussex, UK

set up the 555 as a monostable and use a capicitor in series with the output to pulse the transistor's base when the output changes state after the 10 seconds have elapsed. (there'll bve a pulse to the transistor when it starts too but it'll be the wrong polarity and the transistor will ignore it)

Bye. Jasen

Hi Terry, I gave it another try and Success this time!

Thanks again,

Lawrence

2N3906.

Good - thanks for letting us know.

BTW, *bottom* posting is the favoured standard here.

Terry Pinnell Hobbyist, West Sussex, UK

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