Flasher unit with Dawn Dusk Controller.

Thread Starter

madhavdivya

Joined Jul 20, 2011
11
My requirement is to design a circuit that would provide a LED unit with control vide a dawn / dusk controller and a flasher. A switch helps the user select whether the LED is flashing based on the dawn / dusk controller output (LED flashes in night time only and off during day time) or, keep the LED flasher switched ON all the time, irrespective of day or night.

Here is my circuit for your comments, which will help me improve the circuit. The trim pot at the bottom (220/510) is to indicate the tuned value (approx 220 M Ohm for a flash rate of 1 Hz) and the maximum value (510 M ohm) of the trimpot.
 

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AlbertHall

Joined Jun 4, 2014
8,540
To fully turn on the IRF540 you need at least 10V on the gate. In your circuit, because of the R6/R7 potential divider, you will only get about 4V. Remove these resistors and connect IC2 pin 10 direct to the MOSFET gate.

Resistors R9, R10, and R11 have no function and can be removed without changing the circuit function.
 

ian field

Joined Oct 27, 2012
6,539
My requirement is to design a circuit that would provide a LED unit with control vide a dawn / dusk controller and a flasher. A switch helps the user select whether the LED is flashing based on the dawn / dusk controller output (LED flashes in night time only and off during day time) or, keep the LED flasher switched ON all the time, irrespective of day or night.

Here is my circuit for your comments, which will help me improve the circuit. The trim pot at the bottom (220/510) is to indicate the tuned value (approx 220 M Ohm for a flash rate of 1 Hz) and the maximum value (510 M ohm) of the trimpot.
Several times - I've posted a hand trace of a dusklight outdoor communal lighting unit.

Cadmium sulphide LDRs are becoming scarce and the unit gets away with a regular silicon photo diode which is highly likely to have IR response - but the unit worked just fine with sunlight before it was ripped out for renovations.

The guts of the circuit is a LM358 dual op-amp - a high input impedance voltage follower to accommodate the tiny photo current, and a Schmitt trigger.
 

Thread Starter

madhavdivya

Joined Jul 20, 2011
11
Thanks to all of you for your comments and for guiding me in the right direction. I should have ensured the format prior to posting.

I shall as recommended by you remove R6, R9, R10 & R11. Would not R7 (1K) help in keeping the MOSFET properly turned OFF ?

Thanks in advance.
 

AnalogKid

Joined Aug 1, 2013
8,150
Here is a reduced version that eliminates the 741. It also eliminates the variable hysteresis, but there was nothing in the TS posts indicating why this was necessary.

ak
Night-Flasher-2-c.gif
 

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AlbertHall

Joined Jun 4, 2014
8,540
The circuit should work as shown, but as pointed out it has a few extraneous parts. In fact, IC1, IC2, and most of the parts can be replaced with a single 2N7000 MOSFET. Keep R1, R2, R8, and C5, and Q1 to drive the lamp.

ak
Variable light threshold, variable hysteresis, variable speed selectable flashing, all with one 2N7000? I'd like to see that cicrcuit, please.
 

AnalogKid

Joined Aug 1, 2013
8,150
Variable light threshold, variable hysteresis, variable speed selectable flashing, all with one 2N7000? I'd like to see that circuit, please.
Jumped the gun a bit. One transistor (plus the output driver) for the oscillator with variable speed, and light sensor control. As I drew it up it got too cute for its own good, and probably would operate only over a narrow range of component values.

ak
 

AlbertHall

Joined Jun 4, 2014
8,540
Here is a reduced version that eliminates the 741. It also eliminates the variable hysteresis, but there was nothing in the TS posts indicating why this was necessary.

ak
View attachment 126644
This circuit has a switch which selects between LED solid on regardless of light level, or flashing when it's dark.
The TS requirement is that the switch select between flashing when it's dark or flashing regardless of light level.
 

AnalogKid

Joined Aug 1, 2013
8,150
oops. Missed the second word flasher.
oops^2. Resulting schematic had issues. Fingers on keyboard, brain on Mars.

ak
 
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