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1  Topics / Home Automation and Networked Objects / Re: Garage door safety sensors on: May 02, 2012, 12:36:41 am
I believe there are federal regulations requiring manufacturers of these to make them resistant to defeat or bypass; and my guess is that the companies making them also like to make lots of money selling replacements (that's what happened to me); so naturally they don't want to give you datasheets, etc.
2  Using Arduino / Sensors / Re: Using optical mouse sensor to measure velocity on: April 28, 2012, 10:09:12 pm
Thanks all!  We're still working on this and are excited about using these sensors to develop open-source science teaching tools.  The Parallax sensor would do the job, and I found this interesting site with Arduino-based mouse hacks and even some OSX visualization tools:

3  Using Arduino / Project Guidance / Re: "Camera trap" security design on: April 25, 2012, 11:02:39 pm
Thanks for responses.

AWOL, CHDK could be part of a solution, and could even do the motion detection, but with a lot of time spent learning/hacking; here's a link on that:

zoomkat; thanks, but I've never been able to get any sort of off the shelf PIR light to work around my place, they trigger every few minutes, and they stay on constantly on windy nights.  We also have lots of bugs, maybe crawling over the sensors?  Happens even in winter, though.  We're in s. Illinois, or lot is wild and wooly.

Chagrin, thanks, I suspected that was too long a distance for little IR LED.

Pauly, Triggertrap might do part of the job, but apparently still pre-production.

Much thanks for replies.  Maybe I will figure all this out; looks like a challenge!

At the very least I'd like to have a count of entry into our drive, I'm sure I could figure that out.

4  Using Arduino / Project Guidance / Re: PWM control for high power motor on: April 25, 2012, 12:41:10 pm
Having built pump controllers from scratch, I'll tell I didn't find much "fun" at all in solving all the naggy little problems of making a high power PWM unit.  I'd pay Critical Velocity around $50 for one of their very sophisticated SP-315 series controllers.  These can be run from pots, pushbutton pulses, or TTL signals from your Arduino.

In our lab ( we use them for anything over 8 amps or so, because we could not dream of building anything with that power rating and flexibility for $50.

We use them on pumps up to about 12 amps and they function beautifully, and appear to have some software control to put out a super clean PWM wave.  Also they use a high frequency to avoid audible noise.  The stock Arduino PWM, at about ~500Hz (?) makes an awful buzz with some motors, though you can mess with timers in it to fix that.

My take, hope it helps :-)
5  Using Arduino / Project Guidance / "Camera trap" security design on: April 25, 2012, 12:33:02 pm
I've scoured the Interwebs and this forum and was surprised to find very little information on how to build such a thing.

I live in the woods and suspect somebody's been messing with my stuff.   I'd like to build a system to record photos when a person or car entered my driveway.  I would like to use an IR beam because PIR's will not work well in our very brushy, leafy yard.  We also have a lot of small critters that set them off.

1.  Will the reflector/IR beam system work OK?  I can use a fairly large battery if needed, and the distance would be about 14 feet x 2 (or 8.5m).  In daylight would I need a super bright LED?  Is this a bad idea in general?

2.  I have old Canon digicams around.  Can't figure out how to keep them "awake," though, so there is very little delay between trigger and photo being taken.  I love Canons but they have one dumb design flaw -- the external remote jack is also used for external power!  I'd have to dig into the camera to use both at the same time.  Maybe another brand?

My wife has a new Canon that turns on and takes a photo in about three seconds; that would work if I could get the camera far enough down the driveway to not miss the moving person/object doing the triggering.

Maybe one of you has done somthing like this and I just couldn't find it.  Search terms are "camera trap," and also "trail camera" for commercial units.  All those use PIR, though. 

6  Using Arduino / General Electronics / Re: sensor connectors for use outside on: April 23, 2012, 10:28:38 pm
Shrink tubing with hot-melt adhesive inside is good for watertight connections.  You can find it at a lot of online suppliers and it's even showing up in hardware and automotive supply shops.

You can also put connections inside a watertight enclosure and use gland nuts for your cables to make something that is pretty much watertight.
7  Using Arduino / Motors, Mechanics, and Power / Re: Ball Valve with DC geared motor & encoder on: April 13, 2012, 09:23:37 am
There are solenoid valves that will work with very low pressure, but the ones I use have very small (3/8") orifices.  Since you want to drain your system dry, I wonder if you could use a flapper valve for a toilet tank; all that needs is a short pull; then draining and closing are automatic.  Probably very succeptible to trash in the water, though.
8  Using Arduino / Sensors / Using optical mouse sensor to measure velocity on: April 08, 2012, 07:10:02 pm
We've built an Arduino-powered device that feeds plastic "sand" into river models ( for research and teaching.  It uses a stepper motor and cone valve.

This video shows the business end:

If we can measure the velocity of the particles through the tube, and we know its cross section (it's 0.75 inch diam) we can know the feed rate.

Seems an optical mouse sensor would be perfect.  I see Sparkfun had a breakout for one (, but discontinued it.

And hacking a USB mouse is complicated.  Any ideas?

9  Topics / Science and Measurement / Re: My Pressure & Flow Tester on: April 05, 2012, 11:39:44 am
RobDrizzle; yeah, it's weird, but I learned from this thread there are two interrupt pins, but I still don't understand what happens when they overlap.

Also to OP, we do a lot of plastic fabrication in our lab.  Your enclosure is very cool.  If you have problems with cracking or wear, go with polycarbonate.  A little tricky to cut and glue (don't use high speed saws unless you know what you're doing, if it swarms in the saw, it can fly all over the place at high speed).  It's super tough; not quite as shiny and clear, but you'll never break it in normal use.  Also it really doesn't crack, so no worries with screws close to the edges, etc.  If you want scraps to play with Pmail me.

10  Community / Exhibition / Gallery / Re: Pump controller for river science models. on: April 05, 2012, 11:33:00 am

Yes, but we use a special plastic sand; I've spent 20 years developing all this stuff.  Lots of movies, etc. at  We ship worldwide now, and just shipped number 100 of our 2-meter Em2!  All a labor of love for me, for education and river conservation :-)

11  Community / Exhibition / Gallery / Pump controller for river science models. on: April 04, 2012, 07:26:57 pm
Thanks to many on these forums who helped me develop the "Alix" flow controller for our river models.  The movie says it all.  We're at

We used an Arduino Pro and custom PCB designed by Chris Alix.  The pump's driven by a MOSFET; pretty simple, but the details tooks months to work out.

12  Using Arduino / Sensors / Cool Panasonic GX-12 proximity sensors; hookup question. on: April 04, 2012, 06:18:48 pm
Posting becasue these are very useful sensors and also because I have a question about using them.

I needed a reliable sensor for a limit switch, and found these cool Panasonic sensors:

Extensive data sheet here:

Basically a very small metal detector, with coil and oscillator,  that closes a circuit when anything conductive gets near.  Can be set very precisely; they are very small, and water/oil proof.  Around $30; worth every penny to me.  The indicator light on them is super handy for setting up and troubleshooting.

Two questions, I'm NOT an expert in electronics:  The one I got hold of is a NPN type, see circuit figure attached.  I'm used to open collector PNP sensors; just send the signal wire to an Arduino pin, use external or internal pulldown resistor; look for 5V (HIGH) when on.

But I can't get my head around this one.  I connected the signal to a pin; used the internal pullup resistor with code, and looked for LOW, and this worked perfectly.  Since I don't really understand transistors, I'm assuming the voltage/current OUT of my digital Arduino pin is enough to pass through the transistor in the sensor.  Just the reverse of PNP, right? (And this is "sourcing" v. "sinking," maybe?)

Second, datasheet says this unit needs 12-24V.  I have that available in my setup (from stepper driver), but everything seems to work just fine at 5V.  We will eventually make a lot of science instruments with this thing, will I be OK with 5V for all of them?

Many thanks!  We're developing open source tools for our river models; .

13  Topics / Science and Measurement / Re: My Pressure & Flow Tester on: January 07, 2012, 11:07:32 pm
Very cool.  I've thought of pairing a couple of flow sensors like this (for our science models, see; but how do you handle more than one interrupt with Arduino?

And seems those sensors would have a pretty good pressure drop; unless your flow rates are not that high; that's my problem with the impeller sensors.

And you're a good plumber; if I put the electronics and wet parts in one enclosure they would not last long!  :-)

14  Community / Exhibition / Gallery / Re: Pump controller/flow meter for river model, with code on: November 14, 2011, 11:21:45 pm
Wish I could do that, wildbill, but the  pwm v. flow rate curve is way kinky and requires a fourth order polynomial to properly describe it!  That's why we're using a lookup table.
15  Using Arduino / Project Guidance / Re: "Load mapping" SRAM memory use in Arduino? on: November 14, 2011, 11:18:46 pm
Wow, many thanks you guys!

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