24V 5A 3-state capacitive touch switch (not a dimmer, without relay)

Ya’akov

Joined Jan 27, 2019
9,069
Thanks, you are right of course, but there is also the "wow" factor of the prototype.
So use a touch switch for one of the functions, then add the toggling behavior. By the way, every time I have seen this sort of functionality implemented it‘s been with a little 8-pin μC and a touch switch IC. It is so much easier to implement the logic with the μC no one wants to add more parts to the BoM.
 

sghioto

Joined Dec 31, 2017
5,376
Thanks. What could I use for the ligthing, if it only has to be 1a ? What about using IRF520 or D452 (I see those used a lot, but know nothing about MOSFETs) ?
There are a lot of options as far as switching the audio and lighting.
You could use a N channel mosfet and switch the low side of the LED lightning. Using a RFP50N06 would not require a heatsink as the dissipation is appx 100mw and would eliminate one transistor.
I also replaced Q2 with a BTS500801 ($4.43 at DigiKey)
The BTS50085 is currently not available unless you want to try your luck on ebay or overseas.
Typical dissipation at 5 amps is appx 40mw.
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MisterBill2

Joined Jan 23, 2018
18,167
T avoid copies being made, put everything in one custom IC and then don't let the fab house that makes the IC sell to any others. That will slow the copiers a bit. And patent the physical design.
 

LesJones

Joined Jan 8, 2017
4,174
Rather than switching the power supply to the Bluetooth / audio power amplifier part of your circuit have you considered just muting the audio output. You could just use something like a CD4066 (Quad bilateral switch.) to do that. You have not given any details of the Bluetooth receiver or audio amplifier so it is possible that they already have a mute facility. Switching the power to the amplifie may cause a thump from the speaker at switch on.

Les.
 

DickCappels

Joined Aug 21, 2008
10,153
Build the test switch and get it working. That way you will start to see some weaknesses (and there will be!) and be able to find solutions. You do not want to be doing this with an art knife and jumper wires on your new printed circuit board.
 

Sensacell

Joined Jun 19, 2012
3,432
There is an elephant in the room.

Touch switches depend on subtle and not entirely obvious details of the electrodes and circuit configuration.
Cap sensing circuits require a return path for capacitive currents that must flow in the electrodes.

Just connecting the touch sensing lead to "the frame" might not work at all.

For example, placing a battery powered touch sensing circuit inside a metal box, with only the sense wire connected to the box will yield a total fail. The box acts as a complete shield, touching the outside of the box changes nothing detectable on the inside.

Touch switch products require careful consideration as to how to provide return paths for the sensing electrode currents.
 

MisterBill2

Joined Jan 23, 2018
18,167
certainly there are a variety of "touch-switch"schemes available, including those that detect the ambient electric field from mains wiring to those that detect the loading on an oscillator circuit. Consider those touch-controlled lamps and the interference that they radiate. There are the touch screen systems used on display screens. So there are quite a few rather different methods of sensing available.
Given the requested power switching capability, it seems that this system will be mains powered, which can thus accept a bit more in the "off state" power consumption.
Sorry to muddy the water with a large array of options, but better now than farther along.
 

Thread Starter

oslosl

Joined Jan 13, 2023
173
certainly there are a variety of "touch-switch"schemes available, including those that detect the ambient electric field from mains wiring to those that detect the loading on an oscillator circuit. Consider those touch-controlled lamps and the interference that they radiate. There are the touch screen systems used on display screens. So there are quite a few rather different methods of sensing available.
Given the requested power switching capability, it seems that this system will be mains powered, which can thus accept a bit more in the "off state" power consumption.
Sorry to muddy the water with a large array of options, but better now than farther along.
Battery powered 6x18650.
 

MisterBill2

Joined Jan 23, 2018
18,167
OK, battery operation. But the stated voltage and current seem more toward mains powered.
One caution is that most touch sensor devices draw a constant current so that battery recharging will be required.
Also, 24 volts and even just one amp is a fair amount of power to be drawing from a battery pack. It may be that you have gone through all of that analysis already.
 

LesJones

Joined Jan 8, 2017
4,174
The best true Ah capacity I can find for 18650. cells is 3.5 Ah. (I normally assume about 2.5 Ah.) You will find some being sold on ebay that claim to be higher rating but they are fictitious. So for your device to run for 8 hours it must draw less than about 440 mA. Will this gave the audio output level that you require ?

Les.
 

sghioto

Joined Dec 31, 2017
5,376
One caution is that most touch sensor devices draw a constant current so that battery recharging will be required.
Not the one I designed using the CD40106, less then 1ua which I would highly recommend. Total standby current drain is only about 100ua and 99% of that is the regulator.
 

Thread Starter

oslosl

Joined Jan 13, 2023
173
Thanks all. Here is a photo with the back removed with the internals. Leds are 4,8w/m. It is patent pending. All ideas are very welcome. Please remember: "Space is precious in the Flatlands" 24x24x2" external. Internal depth is 1.2".
 

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LesJones

Joined Jan 8, 2017
4,174
I don't understand your question. If you are suggesting using an N channel mosfet to switch the positive supply to the audio amplifier then you would need to generate a voltage of at least 5 volts more positive than the 24 volt supply. This would be required to drive the gate of the mosfet as the gate has to be driven to be more positive than the source for the mosfet to conduct between source and drain.

Les.
 
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