Touch lamp circuit.

marzan

marzan

Senior Member
Hi everyone. I have a floor lamp that uses a 200W halogen bulb and I am thinking of converting it to a few LED arrays. I want to power it with a 12v wall wart. it is metal so I was thinking of making it a touch lamp. When looking into using the touch sensor on an 08M2 I read that it dosen`t actually work by touch, so can anyone point me in the right direction to find some sort of circuit diagram to connect to a picaxe ? I want to use the PWM function to have about 4 different levels of light. I had a look on Google and couldn`t really find anything that looks like it would hook up to a picaxe.

Thanks.
Marz.
 
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nick12ab

Senior Member
marzan said:
Hi everyone. I have a floor lamp that uses a 200W halogen bulb and I am thinking of converting it to a few LED arrays. I want to power it with a 12v wall wart. it is metal so I was thinking of making it a touch lamp. When looking into using the touch sensor on an 08M2 I read that it dosen`t actually work by touch, so can anyone point me in the right direction to find some sort of circuit diagram to connect to a picaxe ? I want to use the PWM function to have about 4 different levels of light. I had a look on Google and couldn`t really find anything that looks like it would hook up to a picaxe.
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For the PWM control of the LEDs, a MOSFET is a common choice for driving large loads.

For the touch sensitivity, the touch sensitivity on PICAXE works by simply connecting a metal object to a pin on the PICAXE. Have you tried connecting the metal light to the PICAXE using a wire?
 
marzan

marzan

Senior Member
nick12ab said:
For the PWM control of the LEDs, a MOSFET is a common choice for driving large loads.

For the touch sensitivity, the touch sensitivity on PICAXE works by simply connecting a metal object to a pin on the PICAXE. Have you tried connecting the metal light to the PICAXE using a wire?
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I have some IRL540 MOSFETS so that`s what I was going to use. as for the touch connection I was going to do as you suggested, but in the FAQs it said the following:

Note that touch sensors are 'capacitive' so you should not make direct contact with the touch pad or PICAXE pin it is connected to. The touch pad should be separated from your finger touch by thin plastic or other non-conductive material. - See more at: http://www.picaxe.com/FAQs/Interfacing/#sthash.jt1ExE1l.dpuf
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Is that not correct?

Marz.
 
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inglewoodpete

Senior Member
Yes, you are correct Marz. The "touch" (finger) must be insulated from the input pin of the PIC (PICAXE).

Long wires between the PICAXE and the touchpad will pick up every bit of electrical noise around. Don't let me stop you from experimenting but I think the (relatively) high PWM currents for the LEDs (I'm assuming a few 10 or 20W LEDs) will interfere with the sensitive Touch inputs.
 
marzan

marzan

Senior Member
inglewoodpete said:
Yes, you are correct Marz. The "touch" (finger) must be insulated from the input pin of the PIC (PICAXE).

Long wires between the PICAXE and the touchpad will pick up every bit of electrical noise around. Don't let me stop you from experimenting but I think the (relatively) high PWM currents for the LEDs (I'm assuming a few 10 or 20W LEDs) will interfere with the sensitive Touch inputs.
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I will have a bit of a play with it all and post the results. Thanks for the replies everyone :)

Marz
 
W

westaust55

Moderator
As an experiment try some cling wrap around a part of the metalwork as a form of dielectric so you finger becomes one electrode and the metalwork the other electrode/plate as in a capacitor.

Without knowing the arrangement of the light fitting if you have a metal ring around the top (any lamp shade present) isolated from the metal body/post and that were insulated you may do better.
 
A

AllyCat

Senior Member
Hi,

Note that touch sensors are 'capacitive' so you should not make direct contact with the touch pad or PICAXE pin it is connected to.
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So you could connect a capacitor between the metal and the PICaxe pin. I suggest trying between 1 nF and 100 nF (probably the lower value). But as others have said here (and elsewhere), the touch sensors are not easy to get working reliably. It might be better to employ a method which uses the mains "hum" (or PWM noise) rather than trying to work in spite of it.

And in some countries, any exposed metal "should" be connected directly to earth via the mains plug/cable, which is likely to prevent any touch method working.

Cheers, Alan.
 
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inglewoodpete

Senior Member
AllyCat said:
Hi,

So you could connect a capacitor between the metal and the PICaxe pin. I suggest trying between 1 nF and 100 nF (probably the lower value). But as others have said here (and elsewhere), the touch sensors are not easy to get working reliably. It might be better to employ a method which uses the mains "hum" (or PWM noise) rather than trying to work in spite of it.

And in some countries, any exposed metal "should" be connected directly to earth via the mains plug/cable, which is likely to prevent any touch method working.

Cheers, Alan.
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No. You'd still need a touch pad and that whacking great capacitor would either drown you in noise or bypass any chance of registering a touch.

marzan said:
I found this on the `net:
View attachment 15253

http://www.circuitstoday.com/touch-switch-circuit-using-ne-555

Do you think if I modified it by using the circuit up to the transistor and used a voltage divider to an 08M input it could possibly work ?

Marz.
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It may be possible but you've got some serious experimenting a prototyping to do. Touch is very, very touchy! What works on a breadboard may not work on a PCB and vice versa. Having been there I can say that, depending on your skill and experience levels, you have at least 100 hours of development and testing ahead of you - and even then you may have to abandon the idea.
 
marzan

marzan

Senior Member
inglewoodpete said:
No. You'd still need a touch pad and that whacking great capacitor would either drown you in noise or bypass any chance of registering a touch.



It may be possible but you've got some serious experimenting a prototyping to do. Touch is very, very touchy! What works on a breadboard may not work on a PCB and vice versa. Having been there I can say that, depending on your skill and experience levels, you have at least 100 hours of development and testing ahead of you - and even then you may have to abandon the idea.
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I`m up for a challenge !!
Really need to change the 555 from a flip/flop to a momentary switch first I guess.

Marz.
 
T

TheChief

Senior Member
<quote>And in some countries, any exposed metal "should" be connected directly to earth via the mains plug/cable, which is likely to prevent any touch method working. </quote>

This is indeed correct but this could work to your advantage as an easy way of connecting your touch pin to the lamp. As you will no longer need to earth ( bond ) the metal housing because you will not be using mains voltage but extra low voltage 12v you can simply cut the earth wire a few cm from where it is connected to the lamp housing. Now run another wire from your PICAXE and simply tape it in parallel with the original earth wire. By varying the overlap between them you can vary the cap. value. A bit of trial and error will be needed of course.
 
marzan

marzan

Senior Member
TheChief said:
<quote>And in some countries, any exposed metal "should" be connected directly to earth via the mains plug/cable, which is likely to prevent any touch method working. </quote>

This is indeed correct but this could work to your advantage as an easy way of connecting your touch pin to the lamp. As you will no longer need to earth ( bond ) the metal housing because you will not be using mains voltage but extra low voltage 12v you can simply cut the earth wire a few cm from where it is connected to the lamp housing. Now run another wire from your PICAXE and simply tape it in parallel with the original earth wire. By varying the overlap between them you can vary the cap. value. A bit of trial and error will be needed of course.
Click to expand...
If that works it will be AWESOME!! that would save so much extra circuitry. As you pointed out there will not be mains voltage anywhere near the lamp anymore. Power will be supplied from a 12v wall wart.

Marz.
 
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inglewoodpete

Senior Member
I don't want to be a wet blanket but....

I've already explained a couple of times. (I'd love you to prove me wrong!) However, "touch" is not something you can design in your head - you have to get your hands dirty.
 
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