Will this timer work?

On Thu, 26 Mar 2015 20:47:03 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Wed, 25 Mar 2015 12:53:38 -0700, etpm@whidbey.com wrote:

On Mon, 23 Mar 2015 14:55:12 -0500, John Fields
jfields@austininstruments.com> wrote:

On Thu, 19 Mar 2015 10:43:58 -0700, etpm@whidbey.com wrote:

Greetings All,
I have a wire feed welder that I would like to add a stich timer to.
The way it works is when the trigger on the welding gun pressed the
welder turns on for a short time, then turns off for a short time, and
so on until the trigger is released. So I thought I would use a 556
timer because I want to be able to adjust each interval independently.
The intervals are pretty short, from maybe a half second to a few
seconds. I first thought a 555 would work but it seems to me a 556 is
better for adjusting the intervals independently. There used to be a
circuit board available as an option for this welder but it no longer
is. I have the schematic for that board and it used a programmable
timer, the 4536B, and an LM2901 quad comparator, along with a bunch of
other components. Such a complex circuit compared to one using a 556
and a solid state relay makes me wonder if the 556 circuit is
appropriate.
Thanks,
Eric

---
Trying to do the whole thing with a single 555 is pretty nasty since
even with a variable duty cycle used to control the weld time, as
far as I know there's no easy way to change the frequency without
causing interaction with the pulse width.

Using a pair of 555s or a 556, both in monostable mode, would be
appropriate, since you'd use one to determine the time between
stitch welds and the other to determine the weld time.

In use, what you'd do would be to start one of the one-shots when
the trigger was pulled, and then, when that one-shot timed out it'd
trigger the other one which, at the end of its cycle, would start
the cycle anew, generating another round, forever, until the trigger
was released.

Would you like a schematic?

John Fields
Greetings John,
I though I posted a reply to your message above but when looking for
it I don't see it. So, yes please I would love a schematic since it
looks from your post that you are describing what I want. I think.
Thanks,
Eric

---
Here's a link

https://www.dropbox.com/sh/yikxzbjuncr1v6l/AACoSK5d_R2YsKxZTIPGBY4Oa?dl=0

to a schematic and to the .asc file that'll let you run an LTspice
simulation, if you care to.

I opted for a single 555 running as an astable because Tim Wescott
was right; my original dual one-shot circuit could have entered a
hang state with no output without a manual re-start, while this one
is inherently unstable and _MUST_ run, barring some major disaster.

One caveat is that its first output pulse will be about twice as
long as the others, and another is that there's a very slight amount
of interaction between the times when they're being set.

That is, if you set the weld ON time for, say, 100ms and then the
OFF time for 1 second, the ON time will change a tiny bit. Less than
1% as I recall, but you can see it for yourself if you run the sim.

If you decide to use the circuit, make sure that C2 is wired right
at the package, directly across pins 1 and 8.

John Fields

Greetings John,
Thanks for posting the schematic. At first I thought it wouldn't work
for me but I just now realized that the first pulse could be the
non-welding pulse. The reason for the pulsing is to avoid warping of
the metal and a welding pulse twice as long would put too much heat
into the work. But if I use the first pulse as the off weld pulse it
just means a slight delay every time I pull the trigger. In fact,
since I want the gas to flow constantly the extra long pulse at the
beginning of welding will insure there is pure gas flowing when the
first weld starts. I will be connecting the switch in the MIG gun
handle to both the timer and and the gas solenoid controller. I'll let
you know how it works.
Thanks again,
Eric

 

[John Fields]

On Sat, 28 Mar 2015 14:43:51 -0700, etpm@whidbey.com wrote:

On Thu, 26 Mar 2015 20:47:03 -0500, John Fields
jfields@austininstruments.com> wrote:

On Wed, 25 Mar 2015 12:53:38 -0700, etpm@whidbey.com wrote:

On Mon, 23 Mar 2015 14:55:12 -0500, John Fields
jfields@austininstruments.com> wrote:

On Thu, 19 Mar 2015 10:43:58 -0700, etpm@whidbey.com wrote:

Greetings All,
I have a wire feed welder that I would like to add a stich timer to.
The way it works is when the trigger on the welding gun pressed the
welder turns on for a short time, then turns off for a short time, and
so on until the trigger is released. So I thought I would use a 556
timer because I want to be able to adjust each interval independently.
The intervals are pretty short, from maybe a half second to a few
seconds. I first thought a 555 would work but it seems to me a 556 is
better for adjusting the intervals independently. There used to be a
circuit board available as an option for this welder but it no longer
is. I have the schematic for that board and it used a programmable
timer, the 4536B, and an LM2901 quad comparator, along with a bunch of
other components. Such a complex circuit compared to one using a 556
and a solid state relay makes me wonder if the 556 circuit is
appropriate.
Thanks,
Eric

---
Trying to do the whole thing with a single 555 is pretty nasty since
even with a variable duty cycle used to control the weld time, as
far as I know there's no easy way to change the frequency without
causing interaction with the pulse width.

Using a pair of 555s or a 556, both in monostable mode, would be
appropriate, since you'd use one to determine the time between
stitch welds and the other to determine the weld time.

In use, what you'd do would be to start one of the one-shots when
the trigger was pulled, and then, when that one-shot timed out it'd
trigger the other one which, at the end of its cycle, would start
the cycle anew, generating another round, forever, until the trigger
was released.

Would you like a schematic?

John Fields
Greetings John,
I though I posted a reply to your message above but when looking for
it I don't see it. So, yes please I would love a schematic since it
looks from your post that you are describing what I want. I think.
Thanks,
Eric

---
Here's a link

https://www.dropbox.com/sh/yikxzbjuncr1v6l/AACoSK5d_R2YsKxZTIPGBY4Oa?dl=0

to a schematic and to the .asc file that'll let you run an LTspice
simulation, if you care to.

I opted for a single 555 running as an astable because Tim Wescott
was right; my original dual one-shot circuit could have entered a
hang state with no output without a manual re-start, while this one
is inherently unstable and _MUST_ run, barring some major disaster.

One caveat is that its first output pulse will be about twice as
long as the others, and another is that there's a very slight amount
of interaction between the times when they're being set.

That is, if you set the weld ON time for, say, 100ms and then the
OFF time for 1 second, the ON time will change a tiny bit. Less than
1% as I recall, but you can see it for yourself if you run the sim.

If you decide to use the circuit, make sure that C2 is wired right
at the package, directly across pins 1 and 8.

John Fields
Greetings John,
Thanks for posting the schematic. At first I thought it wouldn't work
for me but I just now realized that the first pulse could be the
non-welding pulse. The reason for the pulsing is to avoid warping of
the metal and a welding pulse twice as long would put too much heat
into the work. But if I use the first pulse as the off weld pulse it
just means a slight delay every time I pull the trigger. In fact,
since I want the gas to flow constantly the extra long pulse at the
beginning of welding will insure there is pure gas flowing when the
first weld starts.

---
Excellent!
---

I will be connecting the switch in the MIG gun
handle to both the timer and and the gas solenoid controller. I'll let
you know how it works.
Thanks again,
Eric

---
My pleasure!

John Fields