

HW startup: A journey from (Arduino) idea to product - hansc
http://hwstartup.wordpress.com/2013/09/27/moistly-the-journey-from-arduino-idea-to-product/

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pedalpete
Great write-up, but I have a few questions

1) don't different plants need different amount of moisture in the soil? How
do you account for that?

2) why does moistly check the moisture levels so frequently? Wouldn't hourly
or even daily be more than enough? I assume partly you are checking regularly
because the alarm shouldn't go off after you've done the watering, but what
about checking regularly if the last check was 'dry', but not as regularly if
the last check was 'wet'?

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hansc
Thanks for the nice comment.

To answer your question: 1) Yes, they do. But by measuring the moisture in the
soil, you will get an alarm when a certain amount of water is extracted from
the soil, being caused by heat, sun or a thirsty plant. After quite a bit of
experimentation, we found a threshold value that works for most plants. Not
cactuses ;) 2) Indeed we check more often than needed. But if the plant is
getting dry, we want to briefly signal every five minutes and before we do
that, we do a quick soil check.

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hansc
Love to hear your feedback and reactions

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graphene
Nice read, thanks for sharing.

As an arduino noob, it wasn't clear to me why you need a resonator component,
especially since it isn't present in your first schematic?

Also, have you given thought to what happens after the battery runs out? Can
the battery be replaced by the customer or does the device need to be disposed
of?

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hansc
Thanks for your reply.

The resonator is shown in the 'Eagle schematic', right in the middle of the
picture. The first schematic is just for the moisture sensor. I used it as a
crystal to run the ATMEGA.

When the battery is gone, you just pop open the enclosure and put in a new
CR2032 coin cell battery. You can get those at every gas station or
supermarket.

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graphene
Please bear with me, I'm new to Arduinos/uCs..

So an ATMEGA uC needs an external oscillator to run? Is it to provide the
clock signal or for something else? If so, why doesn't it have its own clock
signal generator? Wouldn't it always need one to run at all?

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hansc
The standard bootloader needs a resonator or crystal to run the oscillator.
You can also program a bootloader which uses the internal oscillator in the
Arduino IDE, in that case no resonator or crystal is used, like I did with the
attiny.

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hclee
This is really inspiring. When choosing most optimized parts, is there a
better way than parametric search in catalogue like Mouser, Digikey or
something??

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hansc
Typically I start with parts that are much used in Arduino projects. Then I
move to Digikey, etc and look for good pricing AND plenty of stock and
multiple vendors. This helps avoiding component related delays.

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hclee
Great advice. I will keep that in mind. Thanks

