Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

"IR based" relay driving problem

Status
Not open for further replies.
J

Javid.zare.s

Guest
hi guys,
ive a lot of problems with ldr circuits and I need it for my hand dryer diy project.
as I emphasised in pictures, I just combined LDR circuit with 3sec 555timer. it doesn't work this way and sadly I don't have ability to design new circuit, so I need your help here.
so
-the goal is to drive a relay for hand dryer , at least stay ON for 3 seconds without shot down, and I want it keep going as long as it detects hand.(smooth, without interrupt)
-of course LED in picture (part2)will be replaced with relay(that was just a simulation to see if it works )
-IR light and reciver will be used(like those which are used in TV control)

IMG_20190116_085818.png
tmp-cam-1658306696.jpg
tmp-cam--697233181.jpg
 

Hi,

You should know: electronics has to do with voltage and currents.
To be able to calculate a circuit, we additionally need to have the datasheets of the used parts.
Thus we need to know the manufacturer, the exact type and the operating conditions of the IR Led and the LDR.

Else all we can do is guess:
My guessing: the 1k at BE of the the BJT is too low in value. Try to use a higher value resistor.

It's simple to measure V_CE to see whether the detector circuit is working properly.
Tell us two values*
* V_CE when no hand is at the detector
* V_CE when the hand is close to the detector

Klaus
 

    V

    Points: 2
    Helpful Answer Positive Rating
Hi,

I think LDRs are very sensitive to any dispersed light and "messy" anyway. You shouldn't need to but you could add a comparator to sense LDR voltage rise/fall to trigger the timer.

If the 3 seconds on time is not truly necessary, you could also take the timing components off the timer, tie 2 and 6 together or use them separately and use them as a window comparator. If there are hands present, output on; if there are no hands present, output off. So long as 1/3 and 2/3 Vcc are acceptable on/off levels (and you can tweak those levels a fair amount without even using pin 5), it's a simple option.

I was messing around with this the other day:

**broken link removed**

Your circuit looks like the positioning/location of the IR LED and LDR are very important to consider and test in the real world at an early stage to get meaningful results.
 

    V

    Points: 2
    Helpful Answer Positive Rating
Hi,

You should know: electronics has to do with voltage and currents.
To be able to calculate a circuit, we additionally need to have the datasheets of the used parts.
Thus we need to know the manufacturer, the exact type and the operating conditions of the IR Led and the LDR.

Else all we can do is guess:
My guessing: the 1k at BE of the the BJT is too low in value. Try to use a higher value resistor.

It's simple to measure V_CE to see whether the detector circuit is working properly.
Tell us two values*
* V_CE when no hand is at the detector
* V_CE when the hand is close to the detector

Klaus

ok, I've changed some values on simulation app.
increased that 1k resistor chases change in current flow direction, but no change in final led current.
also played with other parameters and no success.
(green and yellow in attachment are current flow)
about the v-ce : I have only one IR receiver and im currently testing it out with LDR photoelectric to make sure its working and not blowing of my one and only IR. I gess I get around 1.2 volt at very low amps with ldr
**broken link removed**
----and plz tell me what do you think about this design here: https://www.electroschematics.com/11040/automatic-hand-dryer-circuit/

Hi,

I think LDRs are very sensitive to any dispersed light and "messy" anyway. You shouldn't need to but you could add a comparator to sense LDR voltage rise/fall to trigger the timer.

If the 3 seconds on time is not truly necessary, you could also take the timing components off the timer, tie 2 and 6 together or use them separately and use them as a window comparator. If there are hands present, output on; if there are no hands present, output off. So long as 1/3 and 2/3 Vcc are acceptable on/off levels (and you can tweak those levels a fair amount without even using pin 5), it's a simple option.

I was messing around with this the other day:

**broken link removed**

Your circuit looks like the positioning/location of the IR LED and LDR are very important to consider and test in the real world at an early stage to get meaningful results.

comparator would be a great idea but I actually don't have comparator ic and I prefer not using It to keep the circuit simple and avoiding another purchase.
3 sec timer is not necessary but I need it to be smooth .-will it be smooth?
-and any advises on this design? :
https://www.electroschematics.com/11040/automatic-hand-dryer-circuit/
as you said I want to dismiss the timer side of their design and stick to dryer switching
 
Last edited:

Hi,

about the v-ce : I have only one IR receiver and im currently testing it out with LDR photoelectric to make sure its working and not blowing of my one and only IR. I gess I get around 1.2 volt at very low amps with ldr

Tell us two values*
* V_CE when no hand is at the detector
* V_CE when the hand is close to the detector

Klaus
 

Nice idea but I doubt it will ever work. LDRs are sensitive to a far wider spectrum of light than you want and are also slow to react.

A simple but effective solution is to use a second 555 running in astable mode at around 38KHz, use it to drive the IR LED. Then use a TV remote control receiver module to trigger the delay timer. The advantage is it is filtered to make it insensitive to visible light and other IR sources and the receiver produces pulses that are compatible with the trigger input of the 555.

An important oversight in your original proposal is that the heat source for drying will result in an increase in IR levels and unless you are very careful, also change the output of the LDR by raising its temperature. By using 38KHz pulsed light you completely avoid that problem. The 38KHz frequency comes from it being the commonly used carrier frequency in TV remote control units and consequently the receiver modules have filters in them to reject anything else.

Brian.
 

Hi Javid,

Besides the great advice in previous posts from more experienced members, to answer your questions: I had a quick look at the circuit you link to and - without having tested it or being familiar with it - in principle, it looks workable.

You wouldn't need a comparator using the two comparators inside the 555 (good way to misuse the super little IC).

For a smooth on/off, add a resistor/capacitor combination at the output to the timer or from the BJT to the relay connection - might actually prefer snap-action switching, 'though, or the relay will chatter, I think.

Brian's knowledge and input are worth giving a go if you can get/scavenge the remote control parts somehow.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top