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Capacitive Touch Sensor Breakout - AT42QT1012
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Capacitive Touch Sensor Breakout - AT42QT1012

by Lesliev on Fri Apr 16, 2021 2:05 am

I have recently received this item: Standalone Toggle Capacitive Touch Sensor Breakout - AT42QT1012 PRODUCT ID: 1375
and have it set up on a Breadboard for testing with another Adafruit module: PowerBoost 1000 Charger - Rechargeable 5V Lipo USB Boost @ 1A - 1000C PRODUCT ID: 2465.

I have the following 3 pins of the switch connected to the Powerboost as follows: VDD to Bat, Grnd to GRD(common), Out to Enable on booster. Booster and switch work great but the booster is randomly enabled/disabled and I assume it is by the switch as the led on the switch goes on and off when just sitting untouched on the test bench.
I am obviously missing something here but cant see what that is yet but just want to end up with a touch switch that activates the booster as and when touched.

Hope someone can advise.
Regards

Lesliev
 
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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by Lesliev on Wed Apr 21, 2021 11:22 pm

IMG_6032 (Small).JPG
Powerboost & Touchswitch setup
IMG_6032 (Small).JPG (81.08 KiB) Viewed 208 times
Hello,
I didnt receive a reply to the original post so thought I would try again with some updated information. Essentially the Touch Switch doesnt appear to operate as expected in my setup. I have the Powerboost 1000c outputting 5v to an LED. In my setup I have a 5w 3R3 ceramic resistor inline with the cathode and the LED lights as expected. I have a Lipo 2000mAh connected to the powerboost and the USB is connected to a 3amp powersupply. When the Adafruit Touch Switch is powered via the Powerboost Bat pin (similar result when using the Powerboost Vs pin) the Powerboost board outputs 5v and the LED lights however after a short period 7-20 minutes (shorter time period when using the Vs pin 2-3minutes) the board output stops. If I leave the setup un touched then sometimes after a short period 5-7minutes the Powerboard output will start again but not always and then often if it does start it shuts down shortly after (about 10secs).
If I take the Touch switch out of the circuit and use a slide switch the Powerboard output remains on until I manually turn it off.

So my question is what is happening that the Adafruit Touch switch is causing the Powerboard to disable output after a period, restart again after a period and than disable again? Is it a faulty Touch switch or an inherent design problem in the switch or am I completely wrong in my understanding of the board. The documentation for the switch details the use of the inbuilt timer but advises if not used it is set to infinite, I have not used the Time pin at any time so far so am assuming it is infinite.

Lesliev
 
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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by adafruit_support_bill on Thu Apr 22, 2021 5:47 am

Looks like you have the touch sensor mounted fairly close to the boost converter. It is possible that you are getting some interference from the switching noise of the boost converter. If you separate the two boards, do you still see the same behavior?

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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by Lesliev on Thu Apr 22, 2021 10:28 pm

Thank you for your reply and suggestion. I have tested the switch separated from the powerboard by about 120mm and am still getting the same result with the borad being disabled after about 8 minutes then coming on again for about 5 secs after about 5 minutes. I hope it is'nt the proximity of the two board causing the problem as that would sort of defeat the purpose of using the touch switch for my purposes which is to simply turn a 5v LED portable table lamp on/off. It is a very strange problem as I cant see wha t could be causing the problem in my setup. I have relocated the breadboard connections in case the inserted pins were not making good contact or were causing some sort of additional resistance in the circuit but nothing I have tried has changed the results.
In an earlier post on this forum and in this thread I did ask about using the Touch switch with the Powerboost and was advised it should work just fine b ut so far that has not been the case. I am still wondering if perhaps this touch switch breakout is faulty in some way.
Hope you can suggest something to help resolve the problem
Cheers

EDIT I just checked and it wasn't in this thread but in this one "PowerBoost 1000 Charger - Rechargeable 5V Lipo USB Boost Mod" that it was recommnded to use the Bat, En and Grd pins for the connection.

Lesliev
 
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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by Lesliev on Thu Apr 22, 2021 11:59 pm

Additional information to the above post and thread. I have tested the switch without the enable pin connected to the switch Out pin. The switch in that configutaion appears currently to stay on indefinitely until I touch it when it then goes into its Off state. So the switch appears to be functioning as expected until I connect the Out pin to the Enable pin of the Powerboard at which time something then causes the switch to power off and on randomely and without my physical action.
Dont know what yet this tells us but at least it seems to have narrowed down the problem to the Out/En pin connection. Maybe you can offer a suggestion?

I just reread the Switch documentation and found something I previously missed on page 17 3,.1.5 indicating there is an Auto Off built in to the switch. This seems at odds with the information in the description "We designed this breakout to have infinite time-out. " So does the switch have an Auto Time out enabled as factory standard and shutdown after a while or is it infinite and never shuts down? I am still trying to make sense of the datasheet information regarding this aspect of the switch functioning. Sure hope someone can help.

Lesliev
 
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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by adafruit_support_bill on Fri Apr 23, 2021 5:49 am

So the switch appears to be functioning as expected until I connect the Out pin to the Enable pin of the Powerboard at which time something then causes the switch to power off and on randomely and without my physical action.

That suggests that there may be some interference that is coupling in via the EN pin. You can try adding a small capacitor between EN and GND. If you have access to an oscilloscope, that might shed some light on the nature of the noise.

So does the switch have an Auto Time out enabled as factory standard and shutdown after a while or is it infinite and never shuts down?

The auto-off timer on these boards is disabled by default as described in the documentation. The Time pin is tied to ground. To enable the timer you would need to cut the trace on the back of the board. If it were enabled it would shut off regardless of whether the output was connected to the EN pin or not.

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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by Lesliev on Fri Apr 23, 2021 7:14 am

Thank you for the confirmation. I am still, however, in the dark as to why the touchswitch shuts down after some minutes when the out pin of the switch is connected to the en pin on the powerboost board. It is not a proximity problem as suggested earlier so what is it?
I know this is almost an impossible question to answer from my descriptions but maybe a test setup at your end might help identify either a problem with the switch when connected to the powerboard or a problem in my setup or God knows what.
Would a circuit diagram of my setup help?
I will certainly try a small capacitor as suggested. Maybe you can advise what size you would suggest I try. I do have an oscilloscope and can try to see if there is interference. Are you suggesting i try across the En and Out pin and what should i expect to see as it is only a signal as far as i can determine and not sure what i would find where i measuring across those two points
Regards

Lesliev
 
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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by adafruit_support_bill on Fri Apr 23, 2021 7:55 am

Electromagnetic interference problems can be hard to diagnose. Capacitive touch sensors are basically antennae, so they tend to be more susceptible than something like a mechanical switch. If you have an oscilloscope, connect the ground clip of your probe to GND and probe the EN pin to see what noise might be there. Try it both with and without the connection to OUT.

The optimal filter would depend on the nature of the noise. But sometimes a simple solution is 'good enough'. If you have some capacitors handy, you can try a few to see if they help. I'd probably start with a 0.1uF ceramic cap between EN and GND.

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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by Lesliev on Sat Apr 24, 2021 3:13 am

PB 1000 Osc-Enabled.jpg
PB 1000 Osc-Enabled.jpg (385.51 KiB) Viewed 170 times

PB 1000 Osc-NoEnable.jpg
PB 1000 Osc-NoEnable.jpg (357.43 KiB) Viewed 170 times


I am very much a begiiner in these areas but am learning so thank you for your help. I have attached two screen shots of the Oscilliscope output from the Grd and En pins. One with the Touch switch off so En pin open and one with the touch switch on so En pin grounded. I am not sure they show anything unexpected except that I would have thought when the En pin was open there might have been no signal at all but that doesnt appear to be the case here - of course I could just have my Scope set up wrong!!

I can report that the Touch switch operates as expected until I connect the Out pin to the En pin on the Powerboost board then it only keeps the powerboost 5v on for about 30 secs. So somehow the Switch is being affected by the Powerboost output or the LED it is powering.

I tested with a 1uF capacitor as it was the smallest I had to hand and while it certainly help to keep the switch on longer it still turned off after about 2 minutes. Should I try a bigger capacitor and if so how big and will it just keep the switch on for a longer period but eventually turn off anyway? In my hopes I wanted a switch that acted just like a toggle switch. Press once to turn and press again to turn off. I have an Adafruit mini button switch that I may just have to redesign my product to suit as it seems the Touch switch is not the product for the job I have.
Any comments or advice would be great.

Lesliev
 
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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by adafruit_support_bill on Sat Apr 24, 2021 6:28 am

Looks like the noise is about 6v peak-to-peak at 50 Hz. The boost converter runs at a much higher frequency. Judging from the 50Hz frequency, it is likely coming from something connected to mains voltage. Your circuit may be picking it up from some nearby lighting or electrical equipment.

I am very much a begiiner in these areas but am learning so thank you for your help. I have attached two screen shots of the Oscilliscope output from the Grd and En pins. One with the Touch switch off so En pin open and one with the touch switch on so En pin grounded.

Please also measure with the EN pin disconnected from OUT as requested. We want to make sure we know which side the noise is coming from.

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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by Lesliev on Mon Apr 26, 2021 5:08 am

Thank you for your help. After your last post and after thinking on the problem I couldnt understand where the noise was coming from and why the switch acted in the way it does with seemingly random turn offs. So I discarded all the jumper cables I was using and set up the circuit with an all new batch. I then tested the Grd and En pins with the Osc and the screen shots of those tests are attached and appear to show a very small amount of noise in both configurations but surely not enough to cause a problem. This time I tested with the En pin connected and with the En pin disconnected completely from the switch and given the results thought a faulty jumper cable may have been causing the problem although I had used various cables at various times so not convincing. As said the osc showed no significant noise in either situation. The light came on and stayed on for 70 minutes. Fixed, I thought until it went off:-(
After that setback I was wondering if the USB powersupply could be providing impulses to the Bat pin where the switch was getting its power from. This was something I hadn't tested as the PB had been connected at all times to the USB supply and while the board is supposed to run off USB power if connected I did notice the Battery LED went from Green (full) to Yellow(Charging) after a short period of the LED being on. So I then disconnected the USB supply the LED came on and appears to be remaining on at least I expect until the Lipo battery power drains. I did see that with the USB disconnected the Osc showed an almost perfect straight line with almost no noise and certainly less noise than shown in the attached screen shots taken when the USB was connected. As the OSC is showing pretty much the same as the attached images now but with even less noise I could see no reason to take more screen shots. Hope that is OK.

So is it possible the inbuilt battery charger on the PB is causing fluctuations in the Bat pin voltage when it senses the Bat voltage is low and the TouchButton switch is sensitive to those fluctuations coming in the VDD pin and causing it to shut down? In the configuration with the USB connected and when the switch turns off I can touch the switch to turn the LED on again but it only stays on for about 3-5 secs.
So far the the switch is operating as expected with the USB disconnected.

Hope all this helps and maybe you can suggest a solution or maybe the board design is just not suitable for use with your touch switch. I hope it is Ok but if not then plan B will have to be dreamt up.
Regards
PB OSCEnabled Test2.jpg
PB OSCEnabled Test2.jpg (388.65 KiB) Viewed 147 times

PB OSC-En-Disconnect Test2.jpg
PB OSC-En-Disconnect Test2.jpg (356.49 KiB) Viewed 147 times

Lesliev
 
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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by adafruit_support_bill on Mon Apr 26, 2021 7:30 am

A bad jumper would leave a high-impedance input 'floating'. In that condition it can pick up interference from all kinds of unexpected sources including the mains wiring in your walls. Given the 50Hz noise you were seeing previously, that would be the most likely cause. Your new scope traces appear much better behaved.

Most USB power supplies are 'switching-mode' power supplies. And many of them do have some residual switching noise on the output. Based on your tests, it appears that may be what is causing problems for the capacitive touch switch.

If you have a different supply, you could try that. You could also try adding some more capacitance between the EN and GND pins. You can leave the .1uf ceramic capacitor there, and wire a larger electrolytic on parallel with it.

If you still have interference issues, you may need to use a mechanical on/off switch:
https://www.adafruit.com/?q=on%2Foff&sort=BestMatch

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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by Lesliev on Wed Apr 28, 2021 1:06 am

Thank you yet again. Bit slow responding, sorry. I think your assesment is spot on and while the touch switch is operating much better it still has some problems even with the two capacitors so I agree that plan B might be the solution and as it happens I already have some of the Ada 1683 switches and have previously tested with one and of course it worked just fine. Only problem I have now is how to mount the switch in the bottom of a small lamp base and connect it to the Powerboost board also in the same space in the base.

But that is really just a design problem I think.
Troubleshooting the problem with your guidance has been a great pleasure and tremendous learning experience for me so again thank you.

Lesliev
 
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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by Lesliev on Wed Apr 28, 2021 9:30 pm

Hello again, I have a question regarding the Powerboost charge capability. I have the Powerboost 1000 booster/charger. It is connected to a 3 Amp outlet and has a Lipo 2000mAh battery attached. I have a charge Doctor in the system and it indicates the PB is drawing 510mA. The LED it is running draws 460mA. My understanding of the specs for the board indicates that when it is connected to a USB powersource of sufficient size (3Amp in my case) it should power the LED with no reduction of battery voltage. However in practice I am finding that over a 12 hour period the battery has reduced from 3.77v to 3.2v and am wondering if this is normal and to be expected. Obviously at this rate it will eventually flatten the battery.
Hope you can advise

Lesliev
 
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Re: Capacitive Touch Sensor Breakout - AT42QT1012

by adafruit_support_bill on Thu Apr 29, 2021 9:11 am

Probably best to start a new thread for this and mention PowerBoost in the title.

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