Non-electronics designer looking for design services

fred u

I'm not an electronics engineer, nor do I play one on television.· I'm probably not even what one would consider a hobbyist, really.· I've assembled a few kits and know only extremely basic electronics.· I know which end of a soldering iron is hot, though, and know not to scratch my nose while holding it.· In years past, I've etched a functioning circuit board using a Radio Shack kit of chemicals.

I'm hoping to find someone willing to work with me to design a circuit and would be willing to compensate such a person if the circuit becomes a practical design.

I'd prefer to provide details in email, rather than a post to the forum, but this seems to be the best place to put out feelers.

Rough Overview with some background:

I'm looking for a small package, the size of a pager or thereabouts, which will close a set of contacts (or two sets of contacts, i.e. double pole?) when an external 1.5vdc is applied to an input point for approximately five seconds or less.· The contacts should remain closed for up to 15 minutes, adjustable with a pot or other non-programmed device.· The contacts will carry no more than that provided by standard batteries of not greater than 6vdc and possibly as low as 3vdc.

I chatted with one fellow who suggested a 555 timer but could not get a latch of anything close to 15 mins and the components would be excessively large, he said.

Does anyone think a Basic Stamp could be configured to provide this capability using components available to the average joe?· If· a BS isn't the best option, I'll be happy to entertain anything else that would work.

thanks for your consideration.

fred

Jon Williams

Since you want to operate at 3 volts the SX would probably be the *best* Parallax solution. The code would be trivial, and could be written in SX/B. If the timing isn't super critical, the SX could operate off its internal oscillator. You'd essentially have a single-chip (other than the pot and a cap for it) solution.· You would want to use latching relays, though, because the coil drain on batteries would kill your battery life.

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Jon Williams
Applications Engineer, Parallax

Guenther Daubach

Fred,

I agree with Jon - the SX is good for so many applications - not only for "highly sophisticated" ones. Due to its attractive price it is and interesting replacement for "conventional" circuits, and all this can be done with a minimum of external components. See my sample project at http://forums.parallax.com/showthread.php?p=541621 where I used an SX28 to replace two NE555s together with the discrete components "around" the 555s for pulse-stretching.

Although the SX will be "boared" by just performing such simple tasks - why not? Owning a Porsche, does not mean that you will have to run it at full speed all the time - you can't (should not) do it in the US anyway. Believe it, or not, in Germany most parts of the "Autobahns" still don't have speed limits .

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Greetings from Germany,

G

fred u

I appreciate the quick responses from all of you and also from the private messages I've received.· It's easier to post a global answer here, I think, than to try to repeat myself in so many private messages.

First, to the moderator, I'm not sure what your answer means, because I don't know of the specifications of the devices.·· The timing is not at all critical, to a tolerance of a minute or so is good enough.· I can understand that a latching relay is a good idea, I'm guessing that the circuit can be created to unlatch the relay when desired.

One of the private messages asks how many of these would be constructed and the answer to that is one or two.· This brings to mind the cost of the components needed to build·such a circuit and if an alternative method would be preferable.

Another question was how long should a set of batteries last and I'm going to suggest that this could run on an included 9v battery and I'd hope that it could be configured to last forever but realistically, I haven't a solid idea.· These items would be part of a direct discussion.

I'm not committed to a BS as a solution, but it seemed that a 555 answer was completely out of the picture.

Gunther, I'm glad to hear that the SX is attractively priced, but how attractive is that?· Probably not as attractively priced as a Porsche, I hope!

thanks for the assistance in this effort.

Jon Williams

The SX18DP -- while they last -- is $1.80. I'm sure you could get one of us to program the chips for you so that you don't have to spend money on programming tools (~$80) that you wouldn't use otherwise.

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Jon Williams
Applications Engineer, Parallax

fred u

wow, a buck eighty? that's rather reasonable ! I might have to build three or four just to be on the safe side for the future! Where do I begin?

thanks loads, Jon

PLJack

Jon Williams (Parallax) said...
Since you want to operate at 3 volts the SX would probably be the *best* Parallax solution. .

The SX will run on 3v even?

How did I miss that. Is that true, two 1.5v batteries.

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- - - PLJack - - -

---

Perfection in design is not achieved when there is nothing left to add.
It is achieved when there is nothing left to take away.

fred u

how many hours of operation on a pair of AA batteries?

fred u

Jon, re-reading the thread shows a mis-communications... I did not specify that the device need to operate on 3vdc, only that the output contacts be able to handle 3-6vdc. The device need only operate for as long as possible from batteries contained within, although being able to operate on as low as 3vdc is certainly a plus.

I've also considered that a circuit that closes the contacts on the first application of input trigger and then opens them on the next application of input trigger would work, which ever design would be cost effective and energy efficient.

thanks again,
fred

Jon Williams

That makes it even easier then; finding 5-volt regulators is a no-brainer, 3.3-v devices are not yet as common.

Q: This 3-6 volts ... is it coming from outside? I'm not clear on what you're trying to do.

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Jon Williams
Applications Engineer, Parallax

fred u

Jon,

the input trigger is effectively a 1.5 vdc battery applied to the input points, for lack of a better description. As the battery generating the input trigger drains, I expect the voltage to drop, so the 1.5 vdc may not remain constant. The input trigger voltage remains on the contacts for approx five seconds.

The objective of the circuit, which can be self powered, is to close a switch. That switch will activate another self-powered device, the power of which can be varied, depending on the device connected to the switch. It can be from 1.5vdc (one battery) to 6vdc (four batteries), but not more than that and not a dead short in terms of current draw. The switch should remain closed for 15 minutes (adjustable) or the other option is to make the circuit so that one application of the input trigger closes the switch and the following application opens the switch.

It had been suggested to me in earlier discussions that I could use a solid state switch of some sort if the current flow through the output closure was not excessive, but I'm not qualified to judge what is excessive and what is not.

Jon Williams

You certainly don't want to be using batteries to hold relays closed -- you may be able to find a latching device (that's what's used in my battery-powered thermostat). The input voltage is a bit low, but the SX has an onboard comparitor that can be used to handle that, even over changes.

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Jon Williams
Applications Engineer, Parallax

SPENCE

HTTP://WWW.HOSFELT.COM

5 VDC SPST Dual Coil Latching
$US 0.99
Mfg. - AROMAT
Mfg.# - RSL2D-5V
13/16" x 3/8" x 3/8"
Contact current: 1 amp @ 20 VDC
Coil resistance: 170 ohm
CAT # 45-512

WOULD THIS DO?

73
SPENCE
K4KEP

THEY USUALLY HAVE A ASSORTMENT OF LATCHING LOW VOLTAGE RELAYS. GET THEIR CATALOG.

S

Post Edited (SPENCE) : 8/23/2005 4:04:53 AM GMT

fred u

spence,
thanks for the reference point, although I don't yet have a circuit in hand. I'm guessing that the reference to Dual Coil Latching means that one signal locks the relay in closed position and the next signal opens it? Great price, small size, looks good for the rest of the package, I think, but what do I know?

fred