Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Suggestion on the impact of removing a capacitor in parallel with a tactile Switch

Status
Not open for further replies.

Sink0

Full Member level 6
Joined
Nov 25, 2009
Messages
390
Helped
37
Reputation
74
Reaction score
30
Trophy points
1,308
Location
Sao Paulo, Brazil
Activity points
4,186
Hi,

I have a design that have a tactile switch with the following circuit and an internal pull-up of a microcontroller (about 47k). The capacitor was placed in order to reduce the bounce, but the real debouncing is made inside the firmware.

image3344.png

Would removing the capacitor have any meaningful impact on EMC or EMI of the circuit. It will be tested for IEC 60601-1.

Regards,

Luis
 

barry

Advanced Member level 5
Joined
Mar 31, 2005
Messages
4,986
Helped
1,090
Reputation
2,190
Reaction score
1,074
Trophy points
1,393
Location
California, USA
Activity points
27,288
The capacitor would not hurt emi/emc performance. How much it would help really depends on everything else around it. I would leave the pads for the cap on the board, that way when you go to test it you could easily add the cap if needed. You might also want to put a ferrite bead on the trace running to the switch.
 

Ishaan Karnik

Member level 3
Joined
Jun 16, 2012
Messages
64
Helped
14
Reputation
28
Reaction score
14
Trophy points
1,288
Activity points
1,726
Switch bouncing tends emitt EMI but at low voltage like 3.3V that won't be much of an issue provided you are not working in RF band or some high speed switching protocol like PCI.

This may cause issue with sensitve, high gain amplifier. I have not faced this issue but have heard my co-workers complain about the same. They were working with ultra-sonics.
 

ravindragudi

Full Member level 3
Joined
Jan 20, 2010
Messages
172
Helped
51
Reputation
102
Reaction score
51
Trophy points
1,308
Activity points
2,334
Is there a serious reason to omit the capacitor? If not, then have it on PCB. Even though there is a debounce algorithm in the firmware, containing the switch bounce in the electronics circuit by means of hardware deisgn is best practice. Instead of leaving out the capacitor, you can think of changing the value of capacitor from 100nF to a lower value like 10nF or something.
 

Sink0

Full Member level 6
Joined
Nov 25, 2009
Messages
390
Helped
37
Reputation
74
Reaction score
30
Trophy points
1,308
Location
Sao Paulo, Brazil
Activity points
4,186
Is there a serious reason to omit the capacitor? If not, then have it on PCB. Even though there is a debounce algorithm in the firmware, containing the switch bounce in the electronics circuit by means of hardware deisgn is best practice. Instead of leaving out the capacitor, you can think of changing the value of capacitor from 100nF to a lower value like 10nF or something.
Definately there is a reason: Board space. We need to place a new resistor in the board and we are out of space. When i was checking what could be done, I realized I placed this capacitor inside the board for good practice purposes only... So i was wondering.

Another possibility would be to replace a series resistor we have between microcontroller pin and a logic N-Mosfet's gate (DMG1012UW-7). It is switched in a very low frequency, but I placed a series resistor to avoid ringing. I could start driving it with the microcontroller pull-up resistor. Would that be a solution?
 

ravindragudi

Full Member level 3
Joined
Jan 20, 2010
Messages
172
Helped
51
Reputation
102
Reaction score
51
Trophy points
1,308
Activity points
2,334
It is riskier to cut down on Cs and Rs to free up board space. Instead of that, another tactile switch with smaller profile can be selected. I am not sure if that is an option for you.
 

Sink0

Full Member level 6
Joined
Nov 25, 2009
Messages
390
Helped
37
Reputation
74
Reaction score
30
Trophy points
1,308
Location
Sao Paulo, Brazil
Activity points
4,186
It is riskier to cut down on Cs and Rs to free up board space. Instead of that, another tactile switch with smaller profile can be selected. I am not sure if that is an option for you.
Well,

Not if they were placed there just for good practices and not for real calculated purpose. So i am just revaluating their utility as i see many designs with no capacitor at all at the tactile switch.

Inside the board there is no chance the switch will create problems. The pull-up is about 47k, so very small switching currents. My concerns is regarding the emited radiation to outside the board. It is a werable device so it is quite well isolated circuit. No RF communication.
 

Ishaan Karnik

Member level 3
Joined
Jun 16, 2012
Messages
64
Helped
14
Reputation
28
Reaction score
14
Trophy points
1,288
Activity points
1,726
Well,

Not if they were placed there just for good practices and not for real calculated purpose. So i am just revaluating their utility as i see many designs with no capacitor at all at the tactile switch.

Inside the board there is no chance the switch will create problems. The pull-up is about 47k, so very small switching currents. My concerns is regarding the emited radiation to outside the board. It is a werable device so it is quite well isolated circuit. No RF communication.
Whats your application?
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top