TTP223 Touch Sensor with LED Strip

[Synthwave]

Hello, I am stumped on a touch sensor problem. I am trying to turn on and off a 5v led strip (@0.8amps) using a ttp223 touch sensor, a mosfet (IRLZ44n) and a power source of 5v- and it does not work. The same circuit does work when I am using 12v power source and 12v led strip. However it is easier to power the led strip and touch sensor with the same supply voltage. Any help would be greatly appreciated. p.s. I am barely a hobbyist at this- bear with me.

 

[Harald Kapp]

Welcome to EP.

Show us a circuit diagram of your setup. The IRLZ44N should be controllable by a 5 V gate-source voltage, so the issue is possibly in the wiring of your components.

 

[Synthwave]

Thanks! Here is the wiring set up I am using. The TTP223 Touch sensor can handle up to 5.5volts.

 

[Bluejets]

Try 1k resistor from gate to ground.

 

[Harald Kapp]

Try 1k resistor from gate to ground.

Always a good idea, but doesn't explain why the circuit should work with 12 V. Plus the TTP2223 has an active push-pull output

it does not work.

What does "it does not work" mean specifically?
- LEDs always on?
- LEDs always off?
- simply not reliable?

The output of the 5 V power source my exhibit a voltage drop when the LED strip is turned on. As the sensor is tied to the same power source, this may cause a malfunction of the sensor. You can try to decouple the sensor board by a 10 Ω series resistor betwenn teh 5 V solurce and the 5 V input of the sensor plus a 100 µF capacitor from the 5 V input of the sensor to ground.

 

[Synthwave]

What happens right now is- if I hook it up the way I have been doing it (from my picture) the leds come on right away and stay on and the touch sensor does not come on (it has a little led to let me know when it is on). If I put a 1k from gate to ground it stays the same. If I put a 1k resistor between gate and ground the leds come on and stay on, and the sensor comes on but it does not turn the lights on or off.

I also gave the sensor its own 5 volt power source and connected all grounds, but had the same problem.

Could it be a bad mosfet(s)? I have tried 6 of them (which all do the same thing). Also, even if I only hook up the drain and source on the mosfet with no I/O signal wire connected- the leds come on right away. I may be misunderstanding it, but shouldn’t the source and drain only allow the current through when a signal is sent through the gate?

 

[Harald Kapp]

What happens when you connect Gate to Source without the connection to the sensor?
Are you aare that the drain of teh MOSFET is not only connected to the center pin but also to the metallic tab? Make sure there are no short circuits by the tab connecting (unvoluntarily) to ground potential.

A note on the side: How long are your wires? MOS circuits are sensitive. noise coupled through long wires may cause issues.

 

[Synthwave]

I am doing this all on a breadboard- no long wires. No change when I connect gate to sensor, and there are no shorts to the metallic tab. I tried a different N channel logic mosfet and same results. I have dim and flickering LEDS when all I have hooked up was source and drain- before I have added any of the rest of the components, is that normal?

 

[BobK]

With a floating gate? Yes, that can happen. In fact, it will likely be sensitive to touch!

Bob

 

[Bluejets]

Probably blew the crap out of the sensor when you hooked it up to 12v.

 

[Audioguru]

The datasheet of the touch sensor IC shows that its pin 1 "Q" is the output. But you have the pin 3 "I/O" touch electrode input wrongly connected to the Mosfet.

 

[gorgon]

The pin numbering of the module is correct if it is this version.

 

[gorgon]

Have you tried the TTP223 module on its own, without the LED and MOSFET connected. Does the onboard LED work as normal?
If it is still on, you may have a noise source that trigger the sensor, or you have it too close to the metal conductors inside the breadboard. Try to put the module on some longer wires to get away from the other circuit/ power etc.

 

[Bluejets]

when I am using 12v power source and 12v led strip

As I said , sensor is only 5v.

 

[Audioguru]

As I said , sensor is only 5v.

He is not used a sensor IC, instead he is using a sensor module that might already have a 5V voltage regulator on it.

 

[Bluejets]

"GENERAL DESCRIPTION The TTP223-BA6/TTP223N-BA6 TonTouchTM is a touch pad detector IC which offers 1 touch key. The touching detection IC is designed for replacing traditional direct button key with diverse pad size. Low power consumption and wide operating voltage are the contact key features for DC or AC application.
FEATURES ƒ Operating voltage 2.0V~5.5V"

 

[BobK]

The same circuit does work when I am using 12v power source and 12v led strip. However it is easier to power the led strip and touch sensor with the same supply voltage.

This line from the OP implies that he is using 2 power supplies with the 12V version, presumable 12V and 5V.

Bob

 

[Bluejets]

Yes, I did see that but I also saw where the Op quoted " the same circuit" so anyone's guess as to what really is what.

 

[Audioguru]

We are also guessing about if there is a 5V regulator on the sensor module.

 

[Bluejets]

I already showed a link and a quote from the spec of the sensor the Op quoted as being used that says max 5v5.