InfraRed Tap For Basin

[furrycow]

Hi there, ok, so im a student studying Control Systems at A Level, and have decided to make a project which means that i can turn the taps in a basin on/off using the infra red given off from my hands, ive drawn up my diagram, and was hoping if anyone could give me ideas on how to improve it or if this circuit would actually work in real life (for example i have done something which is physically impossible) Many Thanks

Furrycow

 

[furrycow]

i realised i shouldve explained my circuit a bit more, so here goes:
the majority of the circuit is based around a monostable, because i am going to have two 2 infrared inputs, an on/off one depending on whether hands are there or not, and a timed on, so the water runs for a set amount of time (reason for switch on capacitors to change time length). This circuit is currently just for one tap, and i would have to make another one for the other tap, i have made sure the solenoid runs off 6v in real life, and the op amps i am using are LM324s. i think that make things a bit more clear to you.

 

[akg]

which software u used to draw that diagram ?..that looks cool...

 

[furrycow]

Oh its Crocodile Clips, you can get a demo from their website
http://www.crocodile-clips.com/crocodile/technology/index.jsp

 

[Optikon]

i realised i shouldve explained my circuit a bit more, so here goes:
the majority of the circuit is based around a monostable, because i am going to have two 2 infrared inputs, an on/off one depending on whether hands are there or not, and a timed on, so the water runs for a set amount of time (reason for switch on capacitors to change time length). This circuit is currently just for one tap, and i would have to make another one for the other tap, i have made sure the solenoid runs off 6v in real life, and the op amps i am using are LM324s. i think that make things a bit more clear to you.

This looks very simulatable (is that a word?). I would suggest you try that if you have doubt. Looks like a lot of detail to go over in that design.

 

[furrycow]

Its probably me, but i dont really know what you mean, ive drawn this up on a circuit simulator, and it works fine on there, and today i began breadboarding the circuit, only time will tell if this circuit will work or not! The thing is the resistor values may not be correct, as the 555 "blows up" when a 9v power supply replaces the 6v, and i'm sure a 555 works on 9v volts, so if resistor values affect it like that on the simulator, im just dreading what else is not true. I will write again if the circuit works, so if anyone wishes to do the same thing as me, then its all done nice and hunky dorey.

 

[Russlk]

The problem with your 555 is the diode from pin 3 to ground. It is a short ckt when the output goes positive. You don't need the diode, the 555 output is low impedance and will absorb the relay transient.

 

[panic mode]

huh? that's wrong! i would definitelly use diode and btw. it's oriented correctly.
problems i see are:
- wipers of potentiometers are connected to 0VDC
- what are the two pushbuttons supposed to do? why are they normally open?

 

[Roff]

Why do you need a oneshot? Why not, "no hand, no water"?
Do you need some current-limiting between your LM324 and the transistor base, or does your relay draw an amp?

 

[Roff]

- wipers of potentiometers are connected to 0VDC

That's not the way I would have done it, but it should work.

 

[furrycow]

I have breadbaorded a trial circuit, with the wipers connected to 0v, and this worked as i desired, thinking about it, in a lot of circumstances, the wiper goes to 0v. The pushbuttons are "my hands" in the circuit, the infrared beam would point out into the air, to rebound off my hands and back to the receiver, so i just put the switches in because it was conventional when designing it. And where abouts would you use the diode? Thanks

 

[furrycow]

Ok, just seen a lot of people answer, im trying to go through each one by one, so the diode from pin 3, is actually just protectng the relay, and current will not be able to go through the diode straight from pin 3 to 0v (its the wrong way round for that to happen?)

 

[furrycow]

Sorry im only a novice, oneshot? some technical language thats beyond me? the current is not too high through the LM324s, but have realised that the LM324s need a 9v supply, and therefore i am going to have to introduce a voltage regulator into the circuit so some of the circuit can run off 9, the rest 6v, the reason i have to have it at 6v is that its the switching voltage for my solenoids.

 

[Roff]

Sorry im only a novice, oneshot? some technical language thats beyond me? the current is not too high through the LM324s, but have realised that the LM324s need a 9v supply, and therefore i am going to have to introduce a voltage regulator into the circuit so some of the circuit can run off 9, the rest 6v, the reason i have to have it at 6v is that its the switching voltage for my solenoids.

Oneshot is another term for monostable. Why do you need one?
LM324 is specified to work down to 3 volts. Its short circuit output current is typically 40ma., which is basically what you have with no resistor between the output and the base of your transistor.

 

[furrycow]

im using a monostable, because i need a timed circuit for which the solenoid to remain on, for example, i am having two inputs; a simple on/off for the solenoid depending on whether there are hands present or not, and a timed circuit to let water flow for a certain length of time which is activated when the hands are placed near the other sensor and emitter. And i have read that LM324s run down to 3v, but i am still to achieve such a possibility, i can't get it even to run with a 6v supply, and that was when i was using the op amp in the simplest circuit going, it wouldnt operate. thanks Ron H for the spec

 

[Roff]

Are you aware that if the trigger pulse to a 555 is longer than the programmed pulse width, the output will not return low until the trigger input has returned low? In other words, the trigger pulse has to be shorter than the monostable width for it to work properly, unles that is what you planned. As designed, the result will be if you momentarily trigger the 555, it will time out. If you keep your hand in the beam, it will stay on past the time-out, until you move your hand.

 

[furrycow]

I had actually unintentionally found that out for my self in the simulator, but if a hand is there for longer than the timed period, then this switch potentially becomes the same as the other switch, in which i mean that it will turn off when the hands are removed, and therefore is a bonus on my part as i have used many infrared taps in my time, and its so frustrating when theyre timed, and they just turn off while youre washing youre hands. So its accidental geniosity (a word?). But thanks again Ron for the suggestion, please keep them coming, youre bound to find an undesired fault sometime soon!!

 

[Roff]

I still don't understand why you have two sensors. Is it so that the water will turn off eventually, in case someone has set something in the sink and then walked away?

 

[furrycow]

Ok, so there are two sensors and two receivers, so 2 pairs of sending and receiving. One pair, when activated, sets the taps to run for a given length of time and then shuts off, unless an object such as a pair of hands remain under the tap. The other pair, simply just turns the water on/off depending on whether there is an object there or not. Now just writing this out i think i know what you were getting at before, and that is if someone was to leave somethinig in the sink then it would would until someone removed that item, and not stop, in which case wouldnt be so good. However i have just made the completed circuit i drew on the previous page on a breadboard, and it doesn't work, ive briefly gone over it with a voltmeter, and on touching the transistor i burnt my finger, so im guessing theres something wrong there. This occured when i was running the LM324 off a 9v, just because that worked for me before, i was wondering, is the output voltage of the op-amp similar to the input voltage? And therefore is why the transistor burnt up (because 9v were passing straight through it with no protection?) Well i'm off again to have a look through my circuit with an electricians best friend, the voltmeter. Ill tell you any problems i have to see if any of you can be more wise than me. Shouldnt take much.

 

[Roff]

40ma of base current won't heat up a transistor, so long as it is saturated.
I would guess that your problem is one of the following:
1. The transistor is too small to handle the relay coil current.
2. The collector is shorted to VCC, or the diode across the relay is backwards.
3. You have installed the transistor incorrectly.

The op amp output will go to within approximately 1.5 volt of VCC with no load, but its output is limited to around 40ma under load.

How much current does your relay coil draw?