Turn Fan On for adjustable Time Period (5 Min - 20 Min ).

Hi,

I want to turn on a fan(AC/220V/50H) using IR obstacle Sensor/NPN(NO) Output as the follwing:
1-)While the sensor seeing the object the fan will be on.
2-)If the object passes the sensor the Fan will be on for a certain time varies from (5 Min - 20 Min).

the following Figure show the available wires for me (+12v,-12v,S,-12v)


S: Sensor output(when it see any object the output become -12v)



could anyone help me to design the circuit to do what i need ?

Regards.

A lot of typical motion sensor light fixtures have an auxiliary output wire to power extra lights. That should run your fan, since you need 220 v AC anyway.
Even if it doesn’t have an auxiliary wire, you can get Light Socket Adapters to plug in your fan.
They have a few time on settings.

ClydeCrashKop said:

A lot of typical motion sensor light fixtures have an auxiliary output wire to power extra lights. That should run your fan, since you need 220 v AC anyway.
Even if it doesn’t have an auxiliary wire, you can get Light Socket Adapters to plug in your fan.
They have a few time on settings.

Click to expand...

But i am not using motion sensor .

The ir sensor like this .

Regards

My suggestion for how I would go about it is something like this... But let me first qualify my suggestion by saying that I am quick to reach for an mcu, even when a 555 would work...I know that...I'm just saying how I might look into doing it...and I am typing while thinking.

I would use a voltage regulator (with filtering) to get 5V from the +/- 12V and that would power the MCU - let's say an 8 pin PICAXE - cheap and easy.

The LED side of an optoisolator would be connected to S and -12V. The NPN side would be connected to +5V and ground and and an I/O (input) on the picaxe such that that when the sensor is at +12, the IO is high (5V) and when the sensor is interrupted (goes to -12v) the input to the picaxe is low (0V relative to +5V).

When triggered the picaxe turns on an electro-mechanical relay sufficient to control the fan. Probably needs an NPN transistor to drive the relay and, of course, suppression diode on the coil. If I were ambitious, I might use a solid-state relay.

Once the fan is on, the MCU simply waits until the sensor indicates not-interrupted and then starts the post-interruption delay. When that delay has elapsed, it turns off the relay. Subsequently, it goes back to waiting for the sensor to be interrupted.

The post-interruption delay can be hard-programmed or, given another one or more I/O bits could be switch-selectable for one of n delays.

So, let me guess...you sit on the "throne" triggering the sensor and fan. You are done and get up, but you want to keep the fan going for a while. Do you want to put a methane sensor in there and keep the fan going until a "safe" concentration is reached? Maybe even a sign that illuminates "Enter at your own risk"

That is my thinking (leaving out the last bit)....but I am only typing while thinking...I am certain some non-mcu solutions will be offered and they may be much more suitable.

can i use 7805 to drop 24v(-12/+12v) to 5v if i assume 0.1 A load current ?

emb said:

can i use 7805 to drop 24v(-12/+12v) to 5v if i assume 0.1 A load current ?

Click to expand...

Well dropping 19V at 100mA is 1.9W, so with a decent size heatsink it should probably be OK.

emb said:

can i use 7805 to drop 24v(-12/+12v) to 5v if i assume 0.1 A load current ?

Click to expand...

Nigel Goodwin said:

Well dropping 19V at 100mA is 1.9W, so with a decent size heatsink it should probably be OK.

Click to expand...

Shouldn't the datasheet for the specific '7805' be checked? See a TI datasheet here for example. I would not want to use one where the maximum input V is 25V since you have 24V. But this one has a maximum voltage input of 35V. Actually, I thought that in general 7805s were 35V input max, but looking at your response, you are looking at the Voltage drop to calculate power from the load of 100 mA - is that what you did?

See, I know enough (and sometimes only enough) to blow things up. I would have looked at the input voltage max, checked that box. Then the current I wanted to get out of it for my 5v circuit..100 mA, check...and then worry about a heat sink if I knew I was near the max for the device or if it got hotter than H.

Just being honest, not saying I am right. Can you explain further or are the fundamentals missing (on my part).

DrG said:

then worry about a heat sink if I knew I was near the max for the device or if it got hotter than H.

Click to expand...

1.9W is going to be VERY hot, and presumably hit thermal overload.

Buy an industrial timer relay. Several companies make timer relays they operate on 120v or 240v ac. They come in 100s of different time settings buy one that is 0 to 30 minutes. Use your sensor to turn relay ON when relay times out FAN turns off. Turn knob on top to set the time you want.

I have 74 of these timer relays. I have not found any good projects of these lately. This relay is OLD it is 120vac only, I paid 2 cents per lb for these at the scrap yard.

If you don't want DIY, one of these or something similar might work for you.

According to post #1 there is no power or signal Ground connection. Where is the reference ground for the system? Some of the description implies to me that what you are calling -12 is actually Ground.

Please post a wiring diagram showing *all* power and signal connections.

ak

I found a datasheet. **broken link removed** 24 VDC is a common industrial control panel power. You have 500 mA sik capability. The output is an NPN transistor, so it sinks current to ground,

You hve the NO, NC to sort out NO usually means without the target reflector. With the target or nothing in the baem, it might be closed.
No guarantees at all. You need a load, a pull up or a DVM with a diode function to test.

With the diode function, power the sensor and take the output to ground using the diode function of the DVM with the proper polarity. Figure out what it does.

https://recom-power.com/pdf/Powerline_AC-DC/RAC03-ER_277.pdf makes a low power 24 Vdc (circular disc) power supply that can go in junction boxes,

You can buy delay on make or delay on break modules which are re-trigerable or non-retrigerable or multifunction modules.
Something like this: https://www.automation24.com/multif...reviewPriceListId=1&refID=adwords_shopping_US

But your still left with getting the NPN output to contact closure. That can easily be done with a relay. Let's leave it at that for now. An OPTOMOS relay (an IC) and a resistor can also be used.

So, you have control type relays and finally, the final output or the light your driving.

The timer is not easy to understand.

I have no idea where
the following Figure show the available wires for me (+12v,-12v,S,-12v)
that comes from.

This ALMOST sounds like a bathroom ventilator project. I had a successful one working for a long time, but it needs to be replaced. The controls are located in an attic space.

I used a delay on break timer, so that 20 minutes after the ventilator switch was turned off, the fan would turn off. If I wanted to automate that more, I could sense shower water flow and do it more automagically.

12V could limit your options.