Maker Pro
Maker Pro

555 timer delay design

T

Tater Schuld

Jan 1, 1970
0
well did a couple of delay circuits as per plans on the web and have
some problems. most of those designs the output goes high *for* a
specified period of time. what i would like to happen is to have the
output go high *after* a specified period of time.

I tired hooking up the RC charge circuit to just the threshold and
trigger, and use the discharge as an event starter. when the discharge
is tied to the RC the voltage should discharge down to 1/3v and then
cause the output to go up. am i right on this theory?

I guess it is time to go tinker
 
M

Michael

Jan 1, 1970
0
Tater said:
well did a couple of delay circuits as per plans on the web and have
some problems. most of those designs the output goes high *for* a
specified period of time. what i would like to happen is to have the
output go high *after* a specified period of time.

I tired hooking up the RC charge circuit to just the threshold and
trigger, and use the discharge as an event starter. when the discharge
is tied to the RC the voltage should discharge down to 1/3v and then
cause the output to go up. am i right on this theory?

I guess it is time to go tinker


Use two 555's, one feeding the other, the two capacitively coupled (a
..01uf should work OK). Program the first 555 with your delay value, the
second 555 with your pulse length.
 
T

Terry Pinnell

Jan 1, 1970
0
well did a couple of delay circuits as per plans on the web and have
some problems. most of those designs the output goes high *for* a
specified period of time. what i would like to happen is to have the
output go high *after* a specified period of time.

A specified time after what? Powering up the circuit? Pressing a
button? Using your next capital letter?
I tired hooking up the RC charge circuit to just the threshold and
trigger, and use the discharge as an event starter. when the discharge
is tied to the RC the voltage should discharge down to 1/3v and then
cause the output to go up. am i right on this theory?

I guess it is time to go tinker
Assuming for the moment that you want to trigger at power-up, you
could adapt this:
http://www.terrypin.dial.pipex.com/Images/555MonoByPU.gif
 
R

Rob Paisley

Jan 1, 1970
0
well did a couple of delay circuits as per plans on the web and have
some problems. most of those designs the output goes high *for* a
specified period of time. what i would like to happen is to have the
output go high *after* a specified period of time.

Use two timers and slave the second to the output of the first.

That is, tie the TRIGGER and THRESHOLD of the second timer to the
OUTPUT of the first through a 10k resistor.

The output of the second timer will be the opposite of the first.


I tired hooking up the RC charge circuit to just the threshold and
trigger, and use the discharge as an event starter. when the discharge
is tied to the RC the voltage should discharge down to 1/3v and then
cause the output to go up. am i right on this theory?

Is the timer being used in an Astable or Monostable configuration?

If the DISCHARGE terminal is not used in the RC circuit the voltage
across the capacitor will increase to slightly above 2/3 of the supply
voltage and stop. The OUTPUT will go LOW and stay there.

You could use the DISCHARGE as the 'event starter' by adding a diode
to the circuit so that voltage from the 'event' is not fed into the RC
circuit. The timing of the circuit will be changed slightly.

But the DISCHARGE terminal will give a LOW output and not the HIGH
output that you want.

Rob.
 
T

Tater Schuld

Jan 1, 1970
0
Terry Pinnell said:
A specified time after what? Powering up the circuit? Pressing a
button? Using your next capital letter?

preferably after opening a switch, as if we waited for me to use
capital letters we would easily drain the battery.

Assuming for the moment that you want to trigger at power-up, you
could adapt this:
http://www.terrypin.dial.pipex.com/Images/555MonoByPU.gif

Will look into it. any suggestions for a breakwire situation?
 
T

Terry Pinnell

Jan 1, 1970
0
preferably after opening a switch, as if we waited for me to use
capital letters we would easily drain the battery.

As you see, that's what the circuit below does
Will look into it.

Not a lot to look into really! It's just a matter of altering the RC
values to suit your 'specified period of time'.
any suggestions for a breakwire situation?

Yes. How about explaining what you mean by it? <g>.
 
Top