The articles discusses an automatic door mechanism circuit that responds to the ambient light conditions by keeping the door open during day time and closed during night. Here the application is used for operating a hen house door. The idea was requested by Mr. Gavin Sweet
Technical Specifications
I have a project that I am starting to investigate and was wondering if you had any ideas
The project is to make an automatic door for a hen house, I would like it to be controlled by dawn/dusk to run a 12v motor to open the door then reaching a limit switch to then reverse motor direction when it is dark returning the door down to a second limit switch placed at the bottom of the door (I was also Hoping to put a delay on the door closure of Upto 30 mins)
There are many designs for a timer version of this circuit but this would mean periodic adjustments to the programmable timer.
I hope you can point me in the right direction
Thanks
Gavin Sweet
The Circuit Design
The requested dawn dusk hen house door operator circuit may be witnessed in the above diagram and understood with the help of the following points.
Two 555 IC stages can be seen the proposed design.
The IC1 stage is wired as light activated switch using an LDR as the sensor.
The relay associated with IC1 is held deactivated during day time and vice versa.
IC2 is configured as a set/reset latch flip flop or bistable stage wherein the relay associated with this IC stays activated when SW1 is in the depressed position and deactivated when SW2 is in a pushed ON state.
Let's assume it's day time and the door being fully open, and the door mechanism keeping the SW1 switch pushed ON.
In the above scenario, the IC1 DPDT relay can be assumed to be in the N/C positions, while the IC2 relay in N/O position.
IC2 relay being in the N/O position cuts off the negative supply to the DPDT relay making sure that the motor in this state stays shut off and tightly locked keeping SW1 pressed and ON.
Now, as day light begins to fade and dusk arrives, the LDR senses this and toggles IC1 pin3 low, actuating the DPDT relay whose contacts now change positions towards their respective N/O points.
The above changeover immediately switches ON the motor which starts moving the door mechanism until its fully closed. In the course it releases SW1 rendering IC2 in a standby position.
When the closing procedure ends, SW2 which is positioned at the the other end of the door mechanism responds to the closing of the door pressure resets the IC2 such that its relay now chnages from N/O to N/C. This action instantly cuts off the other negative line to the N/O contacts of the DPDT.aking sure that the motor shuts off again and stays in that position until dawn sets in.
The 2200u capacitor and R3 may be appropriately tweaked for getting a delayed response from IC1 after dawn or dusk transitions are sensed by the LDR
niconoe says
Thanks a lot, I'll try the suggested solutions. I indeed already included C1. I also played with the value of R3 (10k for example), and as expected I can decrease the delay after the threshold is reached. It's at the time the DPDT finally switch to "day mode" that I observed this oscillation.
I'll keep you informed, thanks for the good work and cheers from (exceptionally sunny) Belgium!
Swagatam says
You are most welcome!! I wish you all the best!!
niconoe says
Hi Swagatam,
Great circuit, thanks a lot! I just build it, works fine except a small quirk: when the DPDT relay switch to "day mode", it oscillates (ON/OFF) like crazy for a few seconds, then stabilize. The motor runs fine, I'm just a bit worried about the relay longevity.
Any idea of what the cause could be? I was thinking some back EMF from the motor, but obviously since it runs in both directions I can't avoid this phenomenon by using a diode (like you did on the relay's coils).
Thanks a lot!
Swagatam says
Thanks Niceone, I am glad you could build it successfully.
To rectify the issue, just try connecting a 100uF/25V capacitor in parallel with the relay coil or D1, positive of the cap will go to the positive side of the coil, and the negative to the pin#3 side of the IC…I am sure this will solve the problem….
Swagatam says
if the above doesn't help, you can use a BC547 transistor driver for the DPDT relay exactly as done for the other relay…and connect a 10uF/25V with base/emitter of this trasistor
Swagatam says
….by the way did you include C1 in the design?…the delay caused by C1 itself should be enough to stop any kind of stuttering on the relay.
Yohana Tijala says
hello sir i hope you doing fine,is it possible to use that circuit above instead of closing the door during evening and then opening while someone block the LDR and then it open and vice versa
Swagatam says
hello yohana, the operation can be reversed by simply interchanging the LDR and R1 positions
Unknown says
hi swagatam sir if possible can u provide me ckt dia for digital ic tester using raspberry pi……….
and happy diwali in advance
Swagatam says
I am sorry, at the moment I do not have this circuit, if I happen to find it will surely let you know…
Gavin says
Hi thanks for posting this design, I have a couple of questions whilst I source components/make a parts list. Firstly what is the value of the C1 on the IC2 part of the circuit? How will I tweek R3 to delay dusk activation? Finally there is a DPDT switch at the top of the diagram next to the motor, what is its function, is it to provide override facility to operate the circuit/motor on demand if needed?
Thanks again Gavin
Swagatam says
Please read the previous comment for the answers…..I have mistakenly written R1 instead of R3, please note this correction….
R1 is for setting the dawn/dusk threshold, whereas R3 is for producing a delay after these thresholds are reached.
Gavin says
Hi, thanks for posting this design, I have a few questions whilst I source components/make a parts list. What is the value of C1 on the IC2 part of the circuit? How will I tweek the dusk part of the operation? There is a DPDT switch at the top of the diagram next to the motor, what is its function, is it a toggle type override switch to test functionality and be able to operate the system on demand if necessary?
Thanks again Gavin
Swagatam says
Thanks it's my pleasure!!
The value C1 of IC2 should be 0.01uF.
Increasing the values of R1/C1 in the IC1 stage will proportionately increase the delay period after the dusk threshold is reached, but I am not sure what value would provide 30 minutes delay, it will need to be experimented by trial and error.
The DPDT indication is for the relay, it's not a switch. The relay associated with IC1 is a DPDT type involving a pair of changeover contacts as shown in the figure.
in order to get an override feature, you can add a SPDT switch parallel with the relay contacts of IC2.
Humphrey Mndaka says
Smart idea..keep it up Swagatam.
regards Humphrey
Swagatam says
thank you Humphrey.