How to bypass a touch switch on a humidifier?

[nicofiaba]

Hello. I have a humidifier that I want to turn on remotely according to the value read by an humidity sensor DHT22. The problem is that, even if I control the power supply to the humidifer via a relay module, the humidifer still doesn't turn on. That's because still you need to touch a "touch switch". I was wondering if it was possible to bypass that, so that when i plug the humidifer it immediatly turns on. The switch and the circuit is shown in the figure below: a single wire is going to a breakout board from the sensor. What can I do? Thanks a lot.

 

[danadak]

Any part makings on the 8 pin part ?


Regards, Dana.

 

[nicofiaba]

No indication there. Can it be a microcontroller which elaborates the input from the touch switch? Can I do anything by working on the MOSFET?

 

[fourtytwo]

MOSFET ? is that what Q1 is ?
If so looks like part of an SMPS of some kind given L1 but then we don't know whats on the other side of the board so some more pics would be helpful.

 

[nicofiaba]

On the other side there is absolutely nothing. A2SHB is a n-channel MOSFET: https://datasheet.lcsc.com/lcsc/2008301206_TWGMC-SI2302_C727152.pdf

 

[fourtytwo]

Well you say nothing, component wise but I spy connecting leads, so what is it powered by and what does it connect too, for example the two red wires ?
Ohh that looks like a DC power jack at the top ?

 

[fourtytwo]

Hmm is this thing mains powered or not ? what does your relay switch ?

 

[nicofiaba]

Here more pics. The two red wires are going to the water ultrasonic humidifier, the module itself. They should be vcc and gnd according to the breakout board (WH- and WH+). The single wire, as you can see is connecting the touch sensor (the little circle) to the circuit. The humidifier is power via USB at 5V, that small black thing is the DC connector. My relay module is just going to control a wall outlet where the humidifier will be plugged in. That's why I need it to start whenever it is connected to the outlet.

 

[rjenkinsgb]

The inductor is the confusing thing, but there are no other components to go with that...

What happens if you bridge the WH- wire to the negative input on the power socket? (Contact nearest the board edge)

It should either work - if the touch board is just an on-off switch - or do nothing, if the touch board also provides the high frequency drive to the mist making part.

Don't keep the connection bridged too long in case anything is taking excess current. There is a small possibility of damaging it, but without knowing more there is nothing to do but speculate..

 

[nicofiaba]

Can you explain more precisely which wire should I solder and where? Another information sorry: one press on the touch button is switching the light on and the humidifier, another press and the light turns off leaving just the humidifier on.

 

[ZipZapOuch]

.

 

[AnalogKid]

The inductor is the confusing thing,

It could be a boost inductor that drives a piezo element. Given that the energy to the system is limited by the DC power connector, I doubt that "WH" stands for water heater. But maybe . . .

TS: What type of humidifier is this?

ak

 

[ZipZapOuch]

TS: What type of humidifier is this?

The two red wires are going to the water ultrasonic humidifier, the module itself. They should be vcc and gnd according to the breakout board (WH- and WH+).

 

[Nigel Goodwin]

I agree it's probably a piezo element, and L1 is an auto-transformer to provide it with a high voltage signal - driven from the small mosfet. The 8 pin chip could be a custom device, or it could be an 8 pin microcontroller? - but in either case, it's creating the signal to feed the boost transformer. I suppose you could try connecting the touch button connection to +ve or ground, and see if perhaps that makes it start up when power is applied?.

 

[nicofiaba]

Thank you everyone, I've managed to bypass the problem by changing the humidifier model. I introduced a relay which is controlling a button switch and everything works fine for me now. =)