Light sensor control for motor

Thread Starter

bingdog

Joined Oct 29, 2018
11
I am trying to make a device to run a DC motor based on the output from a light sensor. The sensor has an npn transistor output that is turned on when the sensor sees no light and off when the sensor detects light. I would like the motor to turn off when the sensor output turns off but I want to manually start the motor (regardless of what the sensor outputs) with an off-momentary on switch. I am using a 12v power supply and the motor is a brushed 12V DC gear motor. It has a rated current of 0.6 amps. It should not be necessary to use a speed control with the motor. The motor would typically turn on / off every 5 or 10 seconds. I was thinking I could use a MOSFET to power the motor although perhaps there is a reason to use a relay. I am fairly new to electronic design and would appreciate any help in getting this to work.
 

Thread Starter

bingdog

Joined Oct 29, 2018
11
Looking into how to do this a little, I thought perhaps a monostable 555 timer could be used to accomplish what I want. Would this circuit be something to work with?
motor control1.jpg
 

Thread Starter

bingdog

Joined Oct 29, 2018
11
I see that is not shown right. If this concept seems workable, would there be some guidelines I could use to size the resistors? I am not sure where to start.
 

Thread Starter

bingdog

Joined Oct 29, 2018
11
The sensor is on/off. So this would be a good approach to go forward? Also, should I add a power resistor between the motor and the control circuit?
 

gerstley

Joined Nov 20, 2015
58
After working a bit with the 555 timer circuit I proposed, I am finding it wont work the way I need it to. When the sensor experiences light, it sends a +12v signal to pin 6 of the 555 and shuts the motor off as I desired. The problem is that when pin 2 is grounded to restart the motor, the pin 3 output can not go high while pin 6 is high. In other words, I am unable to restart the motor while the light sensor experiences light. The sensor needs to be in dark for the motor to restart. I need to be able to restart the motor manually no matter what the light sensor experiences. I wonder if there is a simple way to get around this problem.


Also, I should note that the circuit I drew does not work as it is shown. Resistor R2 should not be there. The control wire from the sensor should be the only input on pin 6/7.
 
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