NEED HELP! "easy" Photoresistor run servo project...

Thread Starter

Fox_911

Joined Mar 16, 2017
5
Hi, Im very green to electronics and this "simple" project is getting the best of me. I want to run a servo off a tiny photoresistor and a 9v battery. I would like to keep everything as small as possible.

Specs:
The Photoresistor:
- Min Voltage-150 volt DC
-Max wattage 90 mW
-spectral peak 540nm
-Light resistance 0.5 Mohm
-100 10:0.7 ??
-Responsive time up:20 Down:30
-Illumination resistance 4

The Servo:
-Current draw idle 6mA
-Current draw stall 350mA
-Voltage 4.8 - 8.5V

Thanks for any help!!
Best Regards, Justin
 

LesJones

Joined Jan 8, 2017
3,571
Is the sevo one that you just reverse the supply polarity to reverse the direction or is it a model contol servo that is controlled by pulse length control ? I have never seen a photoresitor with a minimum voltage specification. are you sure 150 volts is NOT the maximum volltage rating ? If the 9 volt battery is a PP3 type it will not provide enough current. You will need a larger capacity battery. (For example 6 AA cells.)

Les.
 

Alec_t

Joined Sep 17, 2013
12,311
Exactly what should the servo do in response to sensed light changes? Take up a position proportional to light brightness?
 

Bernard

Joined Aug 7, 2008
5,788
LDR specs. make no sense to me, just call it 2 meg. dark, 100 ohms light. Just using the U4 ckt. for the hobby type servo, substitute the LDR for R 11 & parallel LDR with 100 k pot. . & see what happens.Servo-control 00000.png
 

Thread Starter

Fox_911

Joined Mar 16, 2017
5
Datasheet or part number and manufacturer of photoresistor please.
That is all the info i have on this device. basically I want a light activated servo i just need to know the components i need to make it work. i want the device as small as possible, its for a drone application.
Best Regards, Justin
 

Thread Starter

Fox_911

Joined Mar 16, 2017
5
Is the sevo one that you just reverse the supply polarity to reverse the direction or is it a model contol servo that is controlled by pulse length control ? I have never seen a photoresitor with a minimum voltage specification. are you sure 150 volts is NOT the maximum volltage rating ? If the 9 volt battery is a PP3 type it will not provide enough current. You will need a larger capacity battery. (For example 6 AA cells.)

Les.
Thanks for the response! this is a rc servo so yes as i understand its a pulse length control. and you are right that was 150 max voltage. As far as the voltage ive seen this run on a 5v battery but not sure of the milliamps.
 

Thread Starter

Fox_911

Joined Mar 16, 2017
5
Exactly what should the servo do in response to sensed light changes? Take up a position proportional to light brigh
Its a servoless payload servo do i would like it to open or close due to light, either one because i can control that. sensitivity does not matter in this application. basically I want a light activated servo i just need to know the components i need to make it work. i want the device as small as possible, its for a drone application.
Best Regards, Justin
 

Thread Starter

Fox_911

Joined Mar 16, 2017
5
LDR specs. make no sense to me, just call it 2 meg. dark, 100 ohms light. Just using the U4 ckt. for the hobby type servo, substitute the LDR for R 11 & parallel LDR with 100 k pot. . & see what happens.View attachment 122703
Thats what the manufacturer gave so that's all i have. basically I want a light activated servo i just need to know the components i need to make it work. i want the device as small as possible, its for a drone application.
Thanks
 

Bernard

Joined Aug 7, 2008
5,788
I'd measure the resistance of the LDR, light, dark & over expected light operating conditions.
I believe a 556 is available in surface mount, not sure of 555.
 

Alec_t

Joined Sep 17, 2013
12,311
Something based on this, perhaps?
LDR-to-Servo.JPG
This should drive a standard servo from one limit to the other when the LDR is in the dark or light respectively. Resistor values might need tweaking depending on the LDR characteristics.
 
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