Hello,

For an application I'm working on I want to use a capacitive touch circuit. I breadboarded the circuit found in this video for now.

It works as needed when the supply voltage is under about 7V. Above 7V, the output stays high. I need it to be able to operate properly with a supply of approximately 9.5V. Never having used gates or flip flops before, I'm not sure what to go after to be able to use a higher supply. I know I can otherwise drop the supply voltage with a resistor or diodes but I'd imagine there's a better way to do it.

Secondly, would there be a way using this circuit to add adjustable sensitivity for the amount of capacitance needed to trigger?

Thanks

 

Try increasing the value of the 2.7k resistor.
I found this circuit was most successful with a resistor of about 33k, but I was using 74HC logic not 4000 series.
To make it variable put a 10k pot in series with the 4013 clock input and a 47pF capacitor from clock to ground.
You might find that some manufacturers‘ 4013s work better than others, as some put a Schmitt trigger on the clock input and some don’t.
Use Nexperia, because they do. It might not matter if you don’t use the delay on the clock input.

 

Thanks, I'll give that a try. I bought Ti parts, quality wise they should be pretty good but I'll grab some other ones too.

 

I really don’t know how we ended up with two different specs for the 4013 and 74HC74, but it‘s been like that as long as I can remember.
if you have slow clock edges, use the Philips part (now Nexperia), or add a 74Hc14 on the input. It‘s not a quality issue, just a different interpretation of the design.

Just put the preset and capacitor on the input to the previous gate (the one connect to pins 8,9 and 10) the you can use any make.

 

So if I'm following you right, maybe I'll try a 74HC132 in place of the 4000 logic gate. From what I can tell from the datasheets the 74HC132 is comparable to the 4093. Is the 74HC132 the gate you used as mentioned in post ?

And I'll try a 74HC74 in place of the 4013 and see how it works?

Thanks

 

So if I'm following you right, maybe I'll try a 74HC132 in place of the 4000 logic gate. From what I can tell from the datasheets the 74HC132 is comparable to the 4093. Is the 74HC132 the gate you used as mentioned in post ?

And I'll try a 74HC74 in place of the 4013 and see how it works?

Thanks

Yes 4093=74hc132 in logic function (but not pin out)

I used the 74hc574 to multiple channel touch panels.

 

I was reading through the data sheets and noticed the max supply for the 74HC series is 6V. I need to run off a 9v battery.

I'm wondering if I'd be better off sticking with the 4000 series because they can take the higher supply voltages rather than trying to drop the voltage beforehand.

I'll try the 33k in place of the 2.7k and see how it works.

 

You could use a linear voltage regulator to drop the voltage.

 

I was reading through the data sheets and noticed the max supply for the 74HC series is 6V. I need to run off a 9v battery.

I'm wondering if I'd be better off sticking with the 4000 series because they can take the higher supply voltages rather than trying to drop the voltage beforehand.

I'll try the 33k in place of the 2.7k and see how it works.

If you're running it from a PP3, then I'd recommend the 4000 series. For two or three AA cells, I'd use HC.

 

You could use a linear voltage regulator to drop the voltage.

I thought about that but wouldn't that increase power consumption vs using components with a higher supply handling?

 

I'm sorry, what is a PP3?

A 9V "transistor" battery. That's the designation.

 

I thought about that but wouldn't that increase power consumption vs using components with a higher supply handling?

You've chosen a terrible power source, do you have a particular reason for it?

 

You've chosen a terrible power source, do you have a particular reason for it?

Agreed, but it is the industry standard source for guitar pedals if an external power supply isn't going to be used. A power supply would not work for this specific application.

 

Agreed, but it is the industry standard source for guitar pedals if an external power supply isn't going to be used. A power supply would not work for this specific application.

It's too bad because it is the most expensive source per Wh among common batteries and far less effective than lithium secondary cells.

Maybe something like these buck converter modules. They are very small, 17 x 5.5mm

​

 

You've chosen a terrible power source, do you have a particular reason for it?

Don't malign the poor old PP3.
It can't be that bad - it's good enough for guitar pedals AND Fluke multimeters!

 

Don't malign the poor old PP3.
It can't be that bad - it's good enough for guitar pedals AND Fluke multimeters!

I have a healthy and honest negative regard for that relic of transistor radios. We stopped needing it long ago but its mere existence perpetuates it. It is so often used in applications it should never be seen in.

One of my very least favorite applications is the two-PP3 opamp monstrosity. Aren't we better than these things now?

 

It's too bad because it is the most expensive source per Wh among common batteries and far less effective than lithium secondary cells.

Maybe something like these buck converter modules. They are very small, 17 x 5.5mm

View attachment 260252​

 

It's too bad because it is the most expensive source per Wh among common batteries and far less effective than lithium secondary cells.

Maybe something like these buck converter modules. They are very small, 17 x 5.5mm

View attachment 260252​

I was looking at something similar from Pololu. I'll give one a try if I need to. Should be more efficient than a linear regulator in this application.

 

You could try 3 npn transistors in Darlington configuration for very high gain leaving the base floating. I made one setup with a piece of wire that you don't have to touch and it works well. Can be adapted for digital.

 

Should be more efficient than a linear regulator in this application.

Probably not for that touch sensor circuit. A small 100ma 5 volt LDO regulator will work cost less and take up less space.
LP2950CZ-5.0
https://www.digikey.com/en/products/detail/texas-instruments/LP2950CZ-5-0-LFT3/12324762