Button interference problem

I have a circuit and software which I have used for years without problems using 12V. I am now wanting to use 20V but have issues with the membrane keypad. Without touching anything it acts as if buttons are being pressed at random intervals. If I use the same circuit powered with 12V instead it works perfect. The power in to the arduino is via a 7805 regulator with caps fitted. The higher voltage is to power the LED's which is switched via mosfets. Even if I totally remove the 20v from the circuit so the only power to the entire circuit is to the arduino via the 7805 the same problem is still there. I am using the internal pullup resistors and have also tried adding external resistors with the same result.

I have a circuit

Which I will not show you because I know you are all mind readers here and don’t need a schematic.

I dont have a diagram as it is something I built about 5 years ago. The circuit is tried and tested and have been using it for about 5 years without problem so is not an issue. With 12v it works perfect its just why the switches could get interference when using 20v even if the only voltage being used is the 5v from the regulator. What is the best way to reduce interference such as capacitors or resistors.

reptilesink:
I dont have a diagram as it is something I built about 5 years ago.
The circuit is tried and tested and have been using it for about 5 years without problem so is not an issue.
With 12v it works perfect its just why the switches could get interference when using 20v even if the only voltage being used is the 5v from the regulator.
What is the best way to reduce interference such as capacitors or resistors.

Hi,
Can I suggest you reverse engineer and draw a schematic.

Is the 7805 regulator that was being fed with 12V, now being fed with 20V?
Is the 20V pure DC?

Does the regulator get hot?
Do you have the recommended capacitors around the 7805 regulator?
Is the 20V being fed to anywhere else in the circuit apart from the 7805 regulator.

Can you post a picture of your project so we can see your component layout.
Thanks… Tom… :slight_smile:

Yes the regulator is now fed by the 20v DC and has capacitors fitted. The regulator does not get hot. I have removed any other voltage from the circuit so that there is only the 5v from the regulator and the problem still exists. All that is connected is the 5v from regulator, rtc and oled display both on i2c and a 4x1 membrane keypad connected to ground and a0, a1, a2 , a3.

It sounds like your new 20V supply may not be clean DC. Where is it from ?

Steve

It's what came with the light unit. I will dig my bench power supply out and try that set at 20v and see what happens. Failing that I will modify the lights to run at 12v but requires a fair bit of work to do so.

reptilesink: The circuit is tried and tested and have been using it for about 5 years without problem so is not an issue.

I don't give a flying fig if you think the circuit is not an issue, I am telling you it is. If something "works" for 5 years and continues to work at 12V but not at 20V the the problem has to be something to do with the circuit. It is sure nothing to do with the software.

I dont have a diagram

Then unless you can produce one by tracing the circuit accurately then you are stuffed.

its just why the switches could get interference when using 20v

Here is some engineering news for you, it can't.

Unless you can come up with more details then you are just wasting everyone's time.

reptilesink: It's what came with the light unit.

You haven't told us what the light unit is so that's not exactly telling us anything useful.

Steve

Grumpy_Mike:
I don’t give a flying fig if you think the circuit is not an issue, I am telling you it is. If something “works” for 5 years and continues to work at 12V but not at 20V the the problem has to be something to do with the circuit. It is sure nothing to do with the software.
Then unless you can produce one by tracing the circuit accurately then you are stuffed.
Here is some engineering news for you, it can’t.

The problem IS the 20v supply NOT the circuit.
I have just put it on a bench supply at 20v and all is fine, working perfect.
So there you go it can.

So there you go it can.

The last time I looked at electronics the power supply IS part of any circuit. Was it an AC power supply?

It's an AC to DC supply holding a constant voltage

Pulling hen’s teeth :slight_smile:

.