# Interfacing interlocks with pic controller

1. ## Re: Interfacing interlocks with pic controller

Hi,

the circuit is correct now.
Hint: instead of 2 x BAT54 you may use one BAT54S

The circuit will protect the input.
But it will not suppress contact bouncing.

* contact bouncing time
* how to calculate tau

Klaus

•

2. ## Re: Interfacing interlocks with pic controller

That is correct.

Brian.

•

3. ## Re: Interfacing interlocks with pic controller

Originally Posted by KlausST
Hi,

the circuit is correct now.
Hint: instead of 2 x BAT54 you may use one BAT54S

The circuit will protect the input.
But it will not suppress contact bouncing.

* contact bouncing time
* how to calculate tau

Klaus
For Tau,

10K X 100nF,then it have to divide by 1000 for milliseconds..?

- - - Updated - - -

Pull up resistor is placed in right position..?
If we using an interlock signal as +5VDC instead of GND means also shall we use this same circuit expect pullup resistor..?

•

4. ## Re: Interfacing interlocks with pic controller

Yes, all correct. The protection is against voltages outside of VSS and VDD so it will work when the interlock is active low or active high, just swap the pull-up resistor for a pull-down instead.

Brian.

5. ## Re: Interfacing interlocks with pic controller

Hi,

No, I don't think this is correct.
There are two series resistors, one for overvoltage protection, the other as filter.
Both corrupt V_IL to the microcontroller input, as they act as resistor divider in combination with the pullup resistor.

Use the pullup resistor at the most left side, then you are safe.
Btw: I'd go more low ohmic with the pullup. I'd say 10mA as switch current is not too much.

Klaus

•

6. ## Re: Interfacing interlocks with pic controller

22K pull up/down with 2K total series resistance to the switch should give a low of 0.4V or a high of 4.4V. Most 5V PICs have a low guaranteed at 0.8V and a high at 2V so technically it should be OK.

As this is an interlock and therefore not driven, I think I would drop the 1K series resistors to say 470 Ohms if there were worries about logic levels not being reached. If in doubt, move the pull up/down resistor to the interlock input instead of the PIC input. The circuit should function exactly the same.

Brian.

--[[ ]]--