So your touch sensor is not working?

sensorWe have all experienced it, you buy something at Aliexpress. It arrives and you confirm receipt before you have time to test everything and then when you finally get around to that… there is a problem.
That happened to me with a TTP223B capacitive touch sensor. Whatever I tried, the output remained low. Slightly frustrated I was looking at the rather simple board and thought that there really couldn’t be much wrong with it.
ttp223-icFound a datasheet of the TTP223B ic that is on this module and started measuring. Well to make a long story short, the input pin (pin 3) seemed to have no connection with the sensorplate. When I would just touch the input pin, it switched very well. According to an application note in the datasheet capacitor C1 should be between  the input and  the ground and as it should be connected it also should be connected to the  sensorplate, which in fact it was. Turns out pin 3 was not connected to anything. A small wire that I soldered between the top of C1 and  pin 3 remedied everything and after that the sensor worked wonder well.
On checking the feedback of people who ordered this sensor, I noticed many experienced the same problem. No doubt the manufacturer (not perse the seller) must have known about this.