[TriEmbed] Advice Needed -

Fri Oct 4 16:33:03 CDT 2013

First of all, I wanted to thank you all for the advice.  I think I have a better sense of some productive paths forward and - of course - a few more questions….

It sounds like I may be getting ahead of myself by jumping straight to designing a custom PCB board.  Also, I was planning on using the ATmega328p but this ATiny may be a better choice as it is cheaper and does not need an external crystal.  So, here is my new list of next steps:

	- I went to YouTube and watched Paul's excellent presentation.  Determine if my program can fit on an ATiny - The sketch compiles to about 4k but I am currently using 4 pins that require PWM output, 1 binary output, 1 binary output, and three analog inputs for a total of 9 IO pins.  This seems to fit on a ATtiny84.  I will need to order one of these and give it a shot.  Until then, I am going to try building the circuit on a breadboard with the 328p and see if I can get it to run without an external crystal.

	- I would like to learn how to use Eagle just for my own edification but, like John's suggestion to build on a perfboard for the testing phase.  I have a few of these and can start on this process right away. As for learning Eagle, I will take Paul's advice and watch some of the YouTube tutorials - just because I think it would be cool to design a circuit board someday.

	- I do have a dependency on some  proprietary parts that Digikey would not have.  One is a submersible pump and the other is the soil moisture sensor.  I think I need to reverse engineer the soil sensor - http://dx.com/p/diy-soil-humidity-sensor-black-yellow-175463 - as I think it may be over-engineered for what I need.  Will also look at www.yourduino.com to see what I can find there.  

	- One area where I need to think about is the power supply.  I am using a SZF280 PVC Mini Water Pump Motor which can draw up to .8 Amps and runs from 3-12V with a 6V standard working voltage.  I was thinking a 6V 1000mA wall wart and splitting the voltage between the relay for the motor and a 7805 circuit for the board.  Is there a better way to do this?

Thank you all again for your help and advice.  I will keep playing - and learning with this project. 

Chip

On Oct 4, 2013, at 1:00 PM, triembed-request at triembed.org wrote:

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>   1. Re: Advice Needed (John Vaughters)
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> Message: 1
> Date: Fri, 4 Oct 2013 06:26:31 -0700 (PDT)
> From: John Vaughters <jvaughters04 at yahoo.com>
> To: "triembed at triembed.org" <triembed at triembed.org>
> Subject: Re: [TriEmbed] Advice Needed
> Message-ID:
> 	<1380893191.33579.YahooMailNeo at web163002.mail.bf1.yahoo.com>
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> 
> 
> Charles,
> 
> It's great to see people trying to turn ideas into actual products. for a significant portion of my career I was involved in design, product development and pricing in the late 90's, with significant experience in board assemblies. I know that technologies have improved and costs have come down, but the development and sourcing has not really changed that much. Even during the rest of most of my career, I have been involved indirectly with the development of products.
> 
> My advice will be based on lack of clarity of your true intentions. Are you selling because you just want to learn and maybe pay for your hobby?, or are you serious about getting a product out there? You don't have to answer that question to me, but you need to know for yourself. The advice below is geared towards getting a working product out with minimal cost and reasonable speed.?
> 
> 1. As already stated, reduce your BOM to the bare minimum, I like the ATiny idea.
> 2. Forget about CAD for now, make prototypes with your reduced BOM and prove your product works
> 3. Use perfboard or bulk FR4, superglue and wires to keep prototype costs down
> 4. Buy manageable components that you can solder yourself for the prototype
> 5. Find a very basic cheap project box to house your prototypes
> 6. Demo the product and test the heck out of it
> 
> Now you have an idea what your product will look like so you will want to begin the final designs which will take several iterations in the design process. This is where you have decide what direction to take. Costs go up rapidly from here. There is no low cost options once you start building boards and design cycles will kill your cost and your time. You may want to sacrifice cost by looking into perf-boards that are a little more expensive, but will allow you to create an actual product that you can sell without custom board build. I say this, because it is probably a very good idea to create an early production product that you can build completely on your own to test the market. Even if you loose a little money on your test sales, it may be much cheaper than going down the road of custom board builds.
> 
> If you screw up custom board builds, you are left with a pile of scrap and a good chunk of change gone. For this reason, I go back to the question of your intentions. Are you bent on learning board building? or you are looking to sell a product? This is very important. Board building is a craft, a real skill. Bad designs cost real money. I have often destroyed things in the sake of learning and consider it more efficient than paying for college classes, but make no mistake it is a learning cost.
> 
> If you get to a point where you think yo have a real product, consider talking to small build board manufacturers. They will save you alot of money in scrap by allowing them to design the board for you, or look for people that contract those services. Don't get me wrong, building your own boards is achievable and not all boards are difficult, but trust these words from significant experience, weigh your choices carefully.?Even with an experienced designer there will be design iterations.?
> 
> A little advice on cost of your project. Take the cost of the typical Newark or Digikey 1000pc price and cut it in half. This will be approximately what a board builder will pay as true cost. Also, do not trust the cost that a board builder shows as component cost, they love to squeeze 20-30% markup into the components, but keep in mind that you will not get that cost reduction until you ramp up the volume. They will tell you your volume is not high enough, but it doesn't matter, they get volume pricing better than they will show you in most cases. Again, you have no recourse for negotiating until you get your volume up. If you find yourself at this point, I cannot stress enough how important it is to have your board design solid. You DO NOT want to have a box full of assembled product that does not work.
> 
> One last piece of consideration. The lowest cost board will be with the smallest components and smallest board size, but you may want to consider a design that is repairable. There is a cost cut off in product volume where boards become throw away, but you will probably find that volume rather high. Investigate several designs that may allow you to repair vs. throw away.
> 
> I wish you the best of luck and please keep us informed of your progress.
> 
> Thanks,
> 
> John Vaughters
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