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1  Community / Website and Forum / Re: Where to post designs? on: June 20, 2011, 02:18:00 am

I have posted a summary and link on the exhibition page.  I think that should cover it.
2  Community / Exhibition / Gallery / Chicken Coop Pop Hole Opener with current measurement circuit on: June 20, 2011, 02:15:36 am
I have built a device using the Atmega 328P, based on the Arduino with motor shield, but have included a current measurement circuit that monitors the current through the L293D drivers and whose output is fed to an analogue pin of the 328.  The current measurement is implemented with a sense resistor feeding a dual op-amp, half being an amplifier and half being a filter.  It uses low side sensing and the design could have had the gain and filter combined but the design is simple and easy to follow / modify.  References to the design tools are included in the write up.

The project is actually a 4 door chicken coop pop hole opener /closer.  It has a Light Dependant Resistor to monitor light levels, pots to set the open/close delay at sunrise/sunset, switches to check the doors have shut and an LED to indicate status.  The software monitors and averages the light level, checks when thresholds are crossed and works out the time of year and time of day from the length of the night.  DC motors drive the doors open and closed.  The current measurement gives an approximation of the load on the motor.  This is good enough to decide if the door is fully open or blocked when closing.

The project could have many other uses requiring multiple drives, mixed analogue/digital sensors and/or current measurement.

The description is too wordy to paste here.  There are several backup documents and everything is available at  The breadboard top view is attached.  PVC covered wires were used because I didn't have any tinned copper wire to hand!
3  Community / Website and Forum / Re: Where to post designs? on: June 18, 2011, 10:35:10 am
Thanks for the links.  I found the page that says "This is the place to post and share your own code, circuit diagrams, tutorials...."  and I think the current monitoring circuit should go under interfacing with hardware.  When I have time I will add it there.

However, I can't see anywhere that has links to complete projects like my pop-hole opener.  Perhaps there isn't one.
4  Community / Website and Forum / Where to post designs? on: June 18, 2011, 05:12:58 am
When I first browsed the Arduino site I am sure I saw a repository for designs.  I can find the software library share but not the hardware share.

I have used an Atmega 328 and Arduino to build a chicken coop pop-hole opener.  The design is based on the Arduino with motor shield but includes a current measurement facility which might be useful to others.  It uses a Light Dependant Resistor to measure light levels and works out what the season is and what the time of day is to open and close 4 pop-holes at appropriate times.

The design is released under GPLv3 and it, along with the research notes are posted at

Where on this site should I post the link please?
5  Forum 2005-2010 (read only) / Interfacing / Re: Can an unpowered DC motor hold up a weight? on: May 15, 2010, 01:10:12 am
Brilliant.  Thanks.

I will look into worm drives but I think a counterweight will be easiest for me; the walls of the chicken coop are double skinned and the weight can live in the cavity.

6  Forum 2005-2010 (read only) / Interfacing / Can an unpowered DC motor hold up a weight? on: May 14, 2010, 01:05:29 pm
I am planning to use Arduino to drive a DC motor with a pulley that will raise the pop hole door of a chicken coop.  This will be like a crane lifting a load.
My question is when you remove the power from the motor will the weight, in this case the door, drop back down to the closed position or will it stay were it is until the door is lowered by driving the motor in reverse?
I am thinking of using a small (few hundred mA) motor with a 50:1 or 100:1 reduction gearing and a very small pulley say 4mm radius and a door weight of 1 or 2 lb.
Any ideas how I work out if the weight will turn the gears and motor please?
I have the idea in my head that the gearbox will not turn, I recall being told that the gearbox would be damaged before the force to turn the output would turn the unpowered motor but it would be nice to know before I choose the motor.
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