Help me solve this design problem PLEEEZ

[funster]

There is an electromagnet at my job that has a 50% duty cycle. That is
it may be on for up to 5 minutes and then off for 5 before using it
again. I want to design a circuit that acts as a time integrator. As
long as a relay is pulled in, the timer is counting up. When the relay
is out, the timer counts down to zero and stays there. If the operator
isn't paying attention, and he goes over 5 minutes, an alarm sounds to
alert him that he is operating the electromagnet outside its design
parameters.
How can this be accomplished? Any suggestions would be appreciated.

 

[Wouter van Ooijen]

How can this be accomplished? Any suggestions would be appreciated.

Get yourself a microcontroller and learn how to use it? Or take an osc
with a chain of up/down counters, alarm connected to the overflow? Or
take an old PC, use the serial or parallel port as input, and write
the application any way you like?



Wouter van Ooijen

-- ------------------------------------
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Webshop for PICs and other electronics
http://www.voti.nl/hvu
Teacher electronics and informatics

 

[[email protected]]

You need an up-down counter and a slow clock - a 32,768 Hz source as
used in watches might serve as the clock, and counting five minutes of
that needs a 24-bit counter, for which you could use the LSI LS7166
24-bit multimode counter (available ex-stock from Farnell). Multi-mode
includes up-down ....

Of course, any single chip microcontroller could handle the job - the
Microchip Technology PIC series comes to mind (and Farnell have pages
of variants for you to chose from) though the Atmel AVR parts are
reputed to be nicer to work with. For this application you'd presumably
clock the microcontroller at 32.768kHz.

 

[Mark Jones]

You need an up-down counter and a slow clock - a 32,768 Hz source as
used in watches might serve as the clock, and counting five minutes of
that needs a 24-bit counter, for which you could use the LSI LS7166
24-bit multimode counter (available ex-stock from Farnell). Multi-mode
includes up-down ....

Of course, any single chip microcontroller could handle the job - the
Microchip Technology PIC series comes to mind (and Farnell have pages
of variants for you to chose from) though the Atmel AVR parts are
reputed to be nicer to work with. For this application you'd presumably
clock the microcontroller at 32.768kHz.

Or, of course he could do the dual 555 thing. One timer for "on time" and one
for "off time", which added with some logic gates allows the first timer to work
and produce an error condition. Sonalert module for audio alert. No 3 months
required to learn PICs.

 

[[email protected]]

Five minutes is too long for anything but a CMOS 555, and even then the
impedance levels are so high that you'd be wise to mount all the timing
components on Teflon/PTFE stand-offs.

Assembly language programming isn't all that difficult, anyway.

 

[John Fields]

Or, of course he could do the dual 555 thing. One timer for "on time" and one
for "off time", which added with some logic gates allows the first timer to work
and produce an error condition. Sonalert module for audio alert. No 3 months
required to learn PICs.

 

[Rich Grise]

There is an electromagnet at my job that has a 50% duty cycle. That is
it may be on for up to 5 minutes and then off for 5 before using it
again. I want to design a circuit that acts as a time integrator. As
long as a relay is pulled in, the timer is counting up. When the relay
is out, the timer counts down to zero and stays there. If the operator
isn't paying attention, and he goes over 5 minutes, an alarm sounds to
alert him that he is operating the electromagnet outside its design
parameters.
How can this be accomplished? Any suggestions would be appreciated.

How about a bank of 74HC190 up/down counters? CLock it at one Hz, which
you could get from a 4060 and watch xtal. You'd have to strap the first
two to count 0-59 and reset, for minutes, then just decode five minutes
and do the alarm thing. When they deenergize the magnet, the D/U' input
gets switched, and it counts down. Add a little logic to stop at 0.

Good Luck!
Rich

 

[funster]

Thanks all... Wow... the talent out there is amazing. And to think
that my company was quoted from an engineering company to do the job
for $30,000. The circuit I named was just the most basic one possible
though. They would have added a recorder and a signal sent up to
supervision when the operator violated the %50 duty cycle requirement.
Keep the suggestions coming though and you may have earned a promotion
for me. LOL

 

[Luhan Monat]

Thanks all... Wow... the talent out there is amazing. And to think
that my company was quoted from an engineering company to do the job
for $30,000. The circuit I named was just the most basic one possible
though. They would have added a recorder and a signal sent up to
supervision when the operator violated the %50 duty cycle requirement.
Keep the suggestions coming though and you may have earned a promotion
for me. LOL

Now you really could use a PIC. External 512K eeprom for recording and
serial-rs232 out to the supervisor. All in a PIC12F629 - 1 dollar in
small quantities.

 

[Frank Bemelman]

Now you really could use a PIC. External 512K eeprom for recording and
serial-rs232 out to the supervisor. All in a PIC12F629 - 1 dollar in
small quantities.

And a spare input to monitor if someone flushed the toilet, and sent
that information to the supervisor as well

 

[mike]

There is an electromagnet at my job that has a 50% duty cycle. That is
it may be on for up to 5 minutes and then off for 5 before using it
again. I want to design a circuit that acts as a time integrator. As
long as a relay is pulled in, the timer is counting up. When the relay
is out, the timer counts down to zero and stays there. If the operator
isn't paying attention, and he goes over 5 minutes, an alarm sounds to
alert him that he is operating the electromagnet outside its design
parameters.
How can this be accomplished? Any suggestions would be appreciated.

OK, let's put on our thinking caps.
Why would anybody want to limit the duty cycle???

If it's heat, put a thermistor on the magnet.
When it gets too hot, turn on the "coffee break" sign.

If you can't get at the magnet, make a heater/heatsink/thermistor
with the same time constant. I'd suggest a snap-action thermal switch,
but make sure it's rated for lots of operations. The little round
jobbers probably aren't.

Never infer a condition when you can (easily) measure it.
mike

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[John Fields]

OK, let's put on our thinking caps.
Why would anybody want to limit the duty cycle???

If it's heat, put a thermistor on the magnet.
When it gets too hot, turn on the "coffee break" sign.

If you can't get at the magnet, make a heater/heatsink/thermistor
with the same time constant. I'd suggest a snap-action thermal switch,
but make sure it's rated for lots of operations. The little round
jobbers probably aren't.

Never infer a condition when you can (easily) measure it.
mike

---
"make a heater/heatsink/thermistor with the same time constant"? Good
luck... Another self-styled expert raises his ugly head and proposes
a half-baked solution with no backup.

Dumbass, the manufacturer of the magnet specifies a 50% duty cycle and
the maximum ON time VS ambient temp, so it should be obvious that if
you keep track of how long it's been on you can figure out when you
have to shut it down, and for how long, without having to build a
physical model to compare it against.

So, take your "hey it's so obvious" thinking cap shit and stick it
back up your ass where it belongs.

 

[mike]

John Fields wrote:
snip

Dumbass, snip

stick it back up your ass where it belongs.

snip
Hmmmmm
Sounds like somebody's not getting enough fiber...
mike

--
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
..
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Wanted 13" LCD for Mitac 6133 Samsung HT13X13-201
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[Jim Thompson]

John Fields wrote:
snip

snip
Hmmmmm
Sounds like somebody's not getting enough fiber...
mike

Bwahahahahahaha!

...Jim Thompson

 

[kell]

Google "timing relay."
Like
http://www.alliedelec.com/cart/ProductListing.asp?ID=302417&Desc=Timing&IND=T&SEARCH=
Look for the one you need, it might be the "delay dropout" type but
that's up to you to figure out. Buy, connect; garner praise for
achieving inexpensive, effective solution.

 

[Fred Bloggs]

There is an electromagnet at my job that has a 50% duty cycle. That is
it may be on for up to 5 minutes and then off for 5 before using it
again. I want to design a circuit that acts as a time integrator. As
long as a relay is pulled in, the timer is counting up. When the relay
is out, the timer counts down to zero and stays there. If the operator
isn't paying attention, and he goes over 5 minutes, an alarm sounds to
alert him that he is operating the electromagnet outside its design
parameters.
How can this be accomplished? Any suggestions would be appreciated.

This is not really a "design" problem yet. What voltage is being
switched onto that solenoid and what kind of access do you have to it?
And you have several things going on here like that 50% maximum limit
applies for on times of 5 minutes but can be higher for lesser on times?
Or do you want a timer that locks out the solenoid for a duration equal
to the preceding on time? Or is the timer to alarm when the operator
exceeds previous off time or 5 minutes whichever comes first? If duty
cycle is the main thing then a simple timer will not be enough.

 

[Bob Eldred]

There is an electromagnet at my job that has a 50% duty cycle. That is
it may be on for up to 5 minutes and then off for 5 before using it
again. I want to design a circuit that acts as a time integrator. As
long as a relay is pulled in, the timer is counting up. When the relay
is out, the timer counts down to zero and stays there. If the operator
isn't paying attention, and he goes over 5 minutes, an alarm sounds to
alert him that he is operating the electromagnet outside its design
parameters.
How can this be accomplished? Any suggestions would be appreciated.

The counter idea as mentioned in a number of the above posts is OK and can
easily be implemented in a PIC or other micro or in IC logic as several have
stated. However, here is another idea that you might consider: Instead of
measuring time, why not measure temperature and run the coil for how ever
long it takes to get to a max temp, maybe 60deg C. and then keep it off
until it returns to a lower temp, maybe 30 or 40 deg C. That way you would
maximize its duty cycle and get more out of when in a cool environment and
not overstress it when hot. Controlling time does not give that flexibility.
I would use the copper winding as the temperature sensing element by
measureing both the voltage and the current in the coil. The resistance of
the copper would be calculated every second or so in a microprocessor and
the temperature calculated or looked up in a table from the resistance and
its TC which I believe changes 0.39% per deg C. A PIC with two A to D
converters built in could easily do this. The A to D's are hooked up with
appropriate scaling resistors to measure the current and voltage. The output
of the micro would be the same as in the other schemes. It's just a thought,
probably worth about what you're paying for it.
Bob

 

[Frank Bemelman]

"Bob Eldred" <[email protected]> schreef in bericht

[snip]

stated. However, here is another idea that you might consider: Instead of
measuring time, why not measure temperature and run the coil for how ever
long it takes to get to a max temp, maybe 60deg C. and then keep it off
until it returns to a lower temp, maybe 30 or 40 deg C. That way you would
maximize its duty cycle and get more out of when in a cool environment and
not overstress it when hot. Controlling time does not give that flexibility.
I would use the copper winding as the temperature sensing element by
measureing both the voltage and the current in the coil. The resistance of

I like that, good idea.

[snip]

 

[[email protected]]

What's the problen with 24 bits? You can buy a 24-bit counter in a
single package off the shelf, or program it in a medium-sized PLD. Itt
would need triple precision arithmetic in a an 8-bit micro, if most of
them didn't have 16-bit counters built in.

It's not like the bad old days, when 24-bits was 6-four bit ripple
counters strung together ......

 

[John Fields]

John Fields wrote:

5 minutes is a little long for a 555, and 24 bits is a little much,
IMO, but a successful marriage might be a single 555 astable with a 20
second period and a 4 bit up-down counter.


Then,

What's the problen with 24 bits? You can buy a 24-bit counter in a
single package off the shelf, or program it in a medium-sized PLD. Itt
would need triple precision arithmetic in a an 8-bit micro, if most of
them didn't have 16-bit counters built in.

It's not like the bad old days, when 24-bits was 6-four bit ripple
counters strung together ......

---
No problem, just pricey. $49.78 from Farnell, (if they had any) plus
the crystal and the oscillator and the glue logic.

Use a 7555, something like an HC193 and the glue logic needed to make
it work the way the OP wants it to, and you're talking probably less
than $5 for the whole thing.

Even less than that would be a cheap 8 bit µC, and all you'd need
there would be the micro and a 32768Hz crystal. Plus, if he wanted to
do temperature instead of (or in addition to) time, a micro with an
external temp sensor (LM71) would do it.