Automatism Photoresistive

Figure 1: Diagram of the automation photoresistor.

thyristor feeds a dc voltage from 12 to 14 V.


I realized this automation to solve a problem that I faced, but I send it because I think it will serve many readers ELM.
Indeed, when I got in my garage at night with headlights turned on and I put out ... I found myself in the dark! Then began the perilous march blindly, arms stretched forward to reach the light switch: so long as my son has not left his tricycle in the middle of the trail!
With this circuit I have completely solved the problem because when I come home at night and it is night, I enter the garage with the headlights turned on, the light of these flood the sensitive surface FTR1 a photoresistor whose resistance decreases as a result of the illumination, allowing the shipment to the gate of thyristor TH1 to a voltage more than enough to do drive.
Once it starts to conduct, its anode is traversed by a current that activates relay RL1 which contacts feed a small bulb 230 V from March to May W (enough that illuminates the garage). Of course, when I cut the headlights, this little lamp is lit: I can then exit the vehicle and reach the main light switch without a hitch.
But the emergency bulb will she have to stay on? How to disable the relay? Well I just open the switch S1 (see Figure 1), which provides the 12 V circuit, then to close it that lights the LED DL1 using night-so that the circuit is powered up next use.
For any adjustment, you must turn on the headlights and slowly turn the cursor trimmer R1 to the photoresist so as to activate the relay, then turn off the lights of the vehicle, opening the switch S1 and then slowly turn the cursor R1 in reverse until extinction of the small bulb.
When it resumes the starting position S1, DL1 lights and not the small bulb: it will remain off until the photocell is illuminated by the headlights. It goes without saying that said photoresistor will be placed at the height of the vehicle headlights.
For my setup, I used a plastic BT152.800 thyristor, which cost me a euro fifty, but a metal model of any type will go equally well, provided that it demands a control current between 10 and 20 mA.

Figure 2: Pinout thyristor and viewed from the front LED.

Component List
R1 ..... 22 k trimmer
R2 ..... 1 k
C1 ...... 22 uF electrolytic
C2 ...... 100 nF polyester
DS1 .... 1N4004 or 1N4007
DL1 .... LED
TH1 .... thyristor BT152.800
FTR1 ... photoresistor
RL1 .... 1 contact relay 12 V
S1 ..... switch


Editor's Note
In another type of application, if you need to order a load more powerful, you can mount a power relay RL1 below: At this time the contacts of RL1 control the feeding of the relay winding power output contacts which control the load.