Debounce Trigger Switches in Extreme Conditions

  • Thread starter TheAnalogKid83
  • Start date
In summary, using a SPDT switch and cross-coupled NAND gates, you can debounce a trigger switch in hardware.
  • #1
TheAnalogKid83
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Hi I am curious about the best way to debounce a trigger switch in hardware.

These switches will be used in extreme conditions(-40 to 85, very strict EMI restrictions, etc.)

My initial idea is to just put a simple low pass filter (RC circuit) on the input from the switch to the microcontroller pin. I'd do some research to figure out what is a good time constant for the application.

Is this acceptable, or do I need to do something more active like schmitt triggers? I'd like to throw in a resistor/cap and call it a day, but I must do a very effective design.

I've no experience, so anyone that can tell me some advice would be appreciated.
 
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  • #2
also, I should say that I'd like to avoid software debouncing code as much as possible if the hardware solution is cheap and easy enough.
 
  • #3
The traditional switch debounce in hardware uses a SPDT switch and cross-coupled NAND gates. Have you seen this circuit? I have to run, but I can google it if you can't find it. (It's also shown in Horowitz and Hill's Art of Electronics in figure 8.42 [1st edition]).
 
  • #4
Spdt??
 
  • #5
TheAnalogKid83 said:
Spdt??

SPDT = Single Pole, Double Throw

Switches are often classified in terms of the number of "poles" and the number of "throws". Check out the table at the start of this wikipedia article about switches:

http://en.wikipedia.org/wiki/Switch

And here's a diagram of how to use a SPDT switch and cross-coupled NAND gates to debounce the switch (see Figure 3):

http://www.elexp.com/t_bounc.htm
 
  • #6
Schmitt trigger might be what you need.
 
  • #7
minorwork said:
Schmitt trigger might be what you need.

That would help with an RC network, but in general no.
 
  • #8
I would use an RC filter + schmitt trigger.

RC alone will fall the rise/down time of the signals and digital circuits need a minimum rise/down time to work properly.
 
  • #9
thank you very much for the help. it looks like the CPU I'm using has a KP module interface with debouncing internal, but I was still curious as to the best way to do it in hardware. Thanks.
 

1. What are debounce trigger switches?

Debounce trigger switches are electronic switches that prevent multiple signals from being registered as a single input. They are commonly used in electronic devices to eliminate false signals caused by mechanical vibrations or electrical noise.

2. How do debounce trigger switches work?

Debounce trigger switches use a mechanical or electronic mechanism to delay the signal for a short period of time, allowing any unwanted noise to dissipate before the switch is activated. This helps to ensure that only the intended signal is registered by the switch.

3. What are extreme conditions for debounce trigger switches?

Extreme conditions for debounce trigger switches refer to environments where there are high levels of mechanical vibrations or electrical noise. This can include industrial settings, outdoor environments, or applications where the switch is exposed to extreme temperatures or moisture.

4. How do debounce trigger switches perform in extreme conditions?

Debounce trigger switches are designed and tested to withstand extreme conditions. They are typically made with durable materials and have built-in protection mechanisms to prevent damage from mechanical stress, moisture, and temperature variations. However, it is important to select the right switch for the specific application to ensure optimal performance.

5. Can debounce trigger switches be used in safety-critical applications?

Yes, debounce trigger switches can be used in safety-critical applications. They are commonly used in medical devices, aerospace and aviation equipment, and other safety-critical systems. However, it is important to carefully select and test the switch to ensure it meets all necessary safety standards and regulations.

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