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Need circuit board designed / prototyped

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Shadman

New Member
I'm new to this whole field, my electrical experience being limited to cars and motorcycle lighting, and my research this morning on the web has been my first foray into circuit board operation and design. Cool stuff!!!!

My need is to have a circuit board designed and prototyped quickly, documented, and have about 300 a year built. These steps do not all have to be done by the same person. I think this could be a relatively easy board to design and prototype, but have no idea how it would be manufactured. I need 99% reliability, so I can't see having my assembly guys build something of this nature. I have a similar board from another industry that uses a digital timer built in, but I want to avoid the programming and other hassel of replicating that board.

The basic purpose of the board is to activate a 110 volt a/c 1/2 horsepower motor and have it run for a selectable number of seconds. It would also have the ability to have a remote control chip built in. My research leads me to believe the board should have the following capabilities:

1. Convert 110V A/C input into 5 volt DC to run the board.

2. Have a 5 V DC terminal, that when the loop is closed by an external momentary switch (push button, light timer, digital light timer), activates the internal timer / relay

3. Mount on the board a high capacity relay. If needed, have the relay located where it can be bonded to an aluminum face plate to act as heat sink. This relay would accept a current from the board to switch on a 1/2 horsepower motor for 15 to 90 seconds. 653-G4A-1AE-DC12 is the Mauser PN I see that will work, part is a g4a-1a-e

3. Utilize a 555 timer chip (?) and 12 position rotary switch with increasing routing of resistors in series to send a current to the motor relay mounted on the board for the following (approximate) time increments:

Off (external momentary switch would not activate the relay)
15 seconds
30 seconds
45 seconds
60 seconds
75 seconds
90 seconds
Continuous run (continuous would just be a direct flow past the 555, right?)

Taranakiguy's quick drawing on this board helped me visualize how the workings of the rotary switch / 555 / resistors might be set up:

8229-5%20to%2030%20Minute%20Timer.gif


4. Incorporate into the resistance run a variable screwdriver adjusted "tuning" potentiometer to fine tune the iming of the 555 to activate the relay for the desired number of seconds. +/- 10% is acceptable for

5. Include a remote control module on the circuit board to activate the 555 timer and relay just like the loop described in #2 above. This would activate the timing chip for the time prescribed on the rotary switch. The circuit board is mounted in a waterproof plastic enclosure and an external antennae would be tapped thru the box and attached to the circuit board to boost range. Desired range is 300 feet, but 100 feet would be acceptable.

6. Have one additional pair of terminals that could deactivate the signal to the relay. Think of this as a kill switch to deactivate the motor in a crisis, regardless of what the rest of the board is doing / thinking.

7. Ideal board size is smaller than 4 by 4 inches. Height can be up to 1.5 inches.

All comments on the feasability, design hurdles, cost, etc... of this board would be much appreciated. I am in a position to need to have this designed and prototyped very quickly. I'm happy to work with students and well as professional.

Thanks!!!

Peter in Houston, TX
 

smanches

New Member
Post what you are trying to accomplish, not how you think it would be accomplished.
 

Shadman

New Member
Post what you are trying to accomplish, not how you think it would be accomplished.

OK, here goes!

Small board, 3 by 4 inches maybe, runs off 110V AC, drives a 1/2 horsepower motor. Activated by remote control or closing of a usually open switch from external source (source varies by customer, can't put it in the board). Runs motor for 0, 15, 30, 45, 60, 75, 90 seconds, or continuously selected on a rotary switch (rotary is a customer requirement).

Thanks!

Peter
 
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marcbarker

New Member
Don't underestimate the total development/prototyping/manufacture lead time for a blank-sheet 'component-level' design. Yes, it may be the cheapest way in the long term, but there are a lot of intermediate steps, and it only takes major setback and you lose the schedule you promised.

To get product to your first clients quickly, you might consider utilising ready-built and tested modules to meet the present requirements. And get these out in the field, working reliably every time, don't take risks, and this stimulates interest in your mk2 product. This will give you more time to think about the mass-produced PCB and possibly revise the requirements. Typically you'd do a pilot, and make up 6 of these which are tested thoroughly in the feild by your cleints/sales staff. It'll be more expensive of course, you probably make a loss too, but the feedback you get from these prototypes is golden, and often make you realise that the design you thought you had was not quite right.

You could for example use an Industrial Timer module with a calibrated dial and relay contacts. Powered by a $5 'mains adaptor'.
 

Shadman

New Member
You could for example use an Industrial Timer module with a calibrated dial and relay contacts. Powered by a $5 'mains adaptor'.

That is what we are currently using, going through about 300 a year with pretty good results. It's put together peacemeal by a small mom and pop shop using about 8 off the shelf components, such as 110v a/c adapter like you'd use for charging a cell phone, 555 external timer, dial potentiometer, remote module, 110 v relay, on off switch, light timer....

They work well, are reliable, and customers trust them. But our goal is to make the new product 1/3 the size and weight, more reliable, with minimal components, fitting in a standard box we are having manufactured overseas.
 

marcbarker

New Member
That is what we are currently using, going through about 300 a year with pretty good results. It's put together peacemeal by a small mom and pop shop using about 8 off the shelf components, such as 110v a/c adapter like you'd use for charging a cell phone, 555 external timer, dial potentiometer, remote module, 110 v relay, on off switch, light timer....

They work well, are reliable, and customers trust them. But our goal is to make the new product 1/3 the size and weight, more reliable, with minimal components, fitting in a standard box we are having manufactured overseas.

OK I can see where you're coming from. How does it perform in humid environments? Is the selector switch sealed insde a box? Why I ask, is the long string of 8 Megohms in series isn't really 'the done thing'. Though I've seen it done before, you're not the only one. If these are mounted on a PCB instead of on the wafer switch, you might have timing error problems something like -50%, if damp or atmospheric conditions get to the PCB. The PCB would likely need to be encapsulated in epoxy

This is a product that I would expect instead to be done with an Arizona Microchip 'PIC' microcontroller. There would be 1/3 the parts on the BOM and probably cheaper and more reliable too. Perhaps you can look down this avenue and prototype a PIC version (in the manner I described earlier posting)?
 
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bailey45

New Member
Possible Simple Solution

You could make this with a frequency divider like a HEF4521B. On times would double on each setting. 15, 30, 60, 120 seconds. A second chip would be need to latch the circuit on for the duration of the on time. With CMOS chips like the 4xxx types the power supply can be a dropping resistor and a transient suppressor of some type.
An isolated driver would mean you could use a 120VAC relay to reduce tyour power supply requirements.

Partial Schematic attached
 

Attachments

  • Timer.pdf
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marcbarker

New Member
You could make this with a frequency divider like a HEF4521B. On times would double on each setting. 15, 30, 60, 120 seconds. A second chip would be need to latch the circuit <..>
Doesn't meet timing requirements, too many parts, not a single-IC solution! :)

But good ideas about powering CMOS, CMOS has wide supply voltage range.

I think a relay could be considered 'isolated' enough from whatever it's driven by.
 
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bailey45

New Member
Yes timing is a little off. The two chips are little less than a PIC microcontroller. The big advantage would be no SW development.
 

marcbarker

New Member
Yes timing is a little off. The two chips are little less than a PIC microcontroller. The big advantage would be no SW development.

Software could probably be free, someone could write it for academic development, and donate it. The incentive for the Donor is that his work operating in a mass-made product in the field. Good to put on CV.
 

Shadman

New Member
Marc, you hit the nail on the head with the software as a school project. I was already considering that path.
 
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