555 timer problem

[RKovach]

I am trying to use two 555 timers to drive automotive ignition coils for
testing and am having problems. I want to use 1 timer in monostable mode to
run the second timer in astable mode to send the ground signal to fire the
coil. I have tested the timers in a breadboard circuit and they each work as
expected individually. The problem I am having is when I try to connect the
output from the first timer to the second timer,(pin #3 on first to pin #4
of the second) the first one will not have the correct pulse duration. It
will only have the output if pin #2 remains grounded. I have also noticed
that I have the same problem with the first timer when I have my scope probe
connected to the output of the second timer, even if they are not connected
to eachother except for the same power and ground. Also, if I do get these
timers to work together, what would be the best transistor to use at the
output of #2 timer to gound the ignition coil?

 

[John Crighton]

On Wed, 20 Oct 2004 00:56:52 -0500, "RKovach" <rkovach@execpc.com>
wrote:

I am trying to use two 555 timers to drive automotive ignition coils for
testing and am having problems. I want to use 1 timer in monostable mode to
run the second timer in astable mode to send the ground signal to fire the
coil. I have tested the timers in a breadboard circuit and they each work as
expected individually. The problem I am having is when I try to connect the
output from the first timer to the second timer,(pin #3 on first to pin #4
of the second) the first one will not have the correct pulse duration. It
will only have the output if pin #2 remains grounded. I have also noticed
that I have the same problem with the first timer when I have my scope probe
connected to the output of the second timer, even if they are not connected
to eachother except for the same power and ground. Also, if I do get these
timers to work together, what would be the best transistor to use at the
output of #2 timer to gound the ignition coil?

Hello R Kovach,
have a look at this article headed "the time machine"
and the following article on the electric fence using an
automotive ignition coil.
http://www.homepower.com/files/electricfence.pdf

This circuit, works the other way round, to the way you
want, the astable then the monostable but it might still
be worth a read through and you might get some ideas.

Regards,
John Crighton
Sydney

 

[Terry Pinnell]

"RKovach" <rkovach@execpc.com> wrote:

I am trying to use two 555 timers to drive automotive ignition coils for
testing and am having problems. I want to use 1 timer in monostable mode to
run the second timer in astable mode to send the ground signal to fire the
coil. I have tested the timers in a breadboard circuit and they each work as
expected individually. The problem I am having is when I try to connect the
output from the first timer to the second timer,(pin #3 on first to pin #4
of the second) the first one will not have the correct pulse duration. It
will only have the output if pin #2 remains grounded. I have also noticed
that I have the same problem with the first timer when I have my scope probe
connected to the output of the second timer, even if they are not connected
to eachother except for the same power and ground. Also, if I do get these
timers to work together, what would be the best transistor to use at the
output of #2 timer to gound the ignition coil?

Assuming you have it configured correctly, it should work OK, as you
see here:
http://www.terrypin.dial.pipex.com/Images/555GatedMono.gif

You've given no details of the coils' specs, so I've simulated that
only simplistically.

--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[Fred Bloggs]

Terry Pinnell wrote:

"RKovach" <rkovach@execpc.com> wrote:


I am trying to use two 555 timers to drive automotive ignition coils for
testing and am having problems. I want to use 1 timer in monostable mode to
run the second timer in astable mode to send the ground signal to fire the
coil. I have tested the timers in a breadboard circuit and they each work as
expected individually. The problem I am having is when I try to connect the
output from the first timer to the second timer,(pin #3 on first to pin #4
of the second) the first one will not have the correct pulse duration. It
will only have the output if pin #2 remains grounded. I have also noticed
that I have the same problem with the first timer when I have my scope probe
connected to the output of the second timer, even if they are not connected
to eachother except for the same power and ground. Also, if I do get these
timers to work together, what would be the best transistor to use at the
output of #2 timer to gound the ignition coil?



Assuming you have it configured correctly, it should work OK, as you
see here:
http://www.terrypin.dial.pipex.com/Images/555GatedMono.gif

You've given no details of the coils' specs, so I've simulated that
only simplistically.

That OP is a troll.

 

[John Crighton]

On Wed, 20 Oct 2004 14:49:03 +0100, Terry Pinnell
<terrypinDELETE@THESEdial.pipex.com> wrote:

<snip>

Assuming you have it configured correctly, it should work OK, as you
see here:
http://www.terrypin.dial.pipex.com/Images/555GatedMono.gif

You've given no details of the coils' specs, so I've simulated that
only simplistically.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Hello Terry,
on your simulator, just for fun,
what happens to the yellow waveform if you
hold the push button switch closed for a longer
time period, say 0.1second or longer.

I seem to remember seeing the monostable start
when the push to close button was released. I was
messing around a while ago with a similar circuit,
not a computer simulator, just using components
on a breadboard. I am just curious to know what
your simulator does.

Regards,
John Crighton
another hobbyist, Sydney

 

[RKovach]

I did not have the 47uF cap (C3) in my circuit. I have added this and now it
works fine.
Thanks for the help.
I have one more question. I have noticed that in all circuits that drive a
relay or coil, diodes are used at the end to protect the circuit. I plan on
using an IRF510 power MOSFET to ground the coil. The specs on this are 100V
max. Do I need the diodes for protection on this circuit? If I do, will this
affect the output of the coil? The purpose of this project is to view the
coil waveform with a scope.
"Fred Bloggs" <nospam@nospam.com> wrote in message
news:4176745D.4080202@nospam.com...

Terry Pinnell wrote:
"RKovach" <rkovach@execpc.com> wrote:


I am trying to use two 555 timers to drive automotive ignition coils for
testing and am having problems. I want to use 1 timer in monostable mode
to
run the second timer in astable mode to send the ground signal to fire
the
coil. I have tested the timers in a breadboard circuit and they each
work as
expected individually. The problem I am having is when I try to connect
the
output from the first timer to the second timer,(pin #3 on first to pin
#4
of the second) the first one will not have the correct pulse duration.
It
will only have the output if pin #2 remains grounded. I have also
noticed
that I have the same problem with the first timer when I have my scope
probe
connected to the output of the second timer, even if they are not
connected
to eachother except for the same power and ground. Also, if I do get
these
timers to work together, what would be the best transistor to use at the
output of #2 timer to gound the ignition coil?



Assuming you have it configured correctly, it should work OK, as you
see here:
http://www.terrypin.dial.pipex.com/Images/555GatedMono.gif

You've given no details of the coils' specs, so I've simulated that
only simplistically.


That OP is a troll.