Wondering why a pull down resistor value affects a circuit so much, i'm using a pic12f675 with a simple circuit to turn on a led for a few seconds via a micro wave sensor producing a high when movement is detected. When i use any value more than around 470R, it runs the circuit b4 receiving a high from the sensor, e.g. a 1k; 10k, 56k.

It should not be skiping the comand: BTFSS, GPIO,0. I have circuit tied low with a 470R, only now is the circuit stable / not false triggering.

Thanks
Ernie H.

 

You need to provide us with a Schematic-Diagram.
.
.
.

 

You can determine the correct value of pullup/pulldown resistor to use by calculation.

You need to read the device datasheet to find the applicable current and voltage.

For the value of the pulldown resistor, find the logic-low input voltage threshold and the current out of the input pin.

 

You need to provide us with a Schematic-Diagram.

AND electrical specifications of the output of the 'micro wave sensor' that you are using.

 

For the value of the pulldown resistor, find the logic-low input voltage threshold and the current out of the input pin

The current out of the PIC input is max 1uV. 100K resistor is overkill.

I suspect the problem is with the sensor.

 

Wondering why a pull down resistor value affects a circuit so much, i'm using a pic12f675 with a simple circuit to turn on a led for a few seconds via a micro wave sensor producing a high when movement is detected. When i use any value more than around 470R, it runs the circuit b4 receiving a high from the sensor, e.g. a 1k; 10k, 56k.

It should not be skiping the comand: BTFSS, GPIO,0. I have circuit tied low with a 470R, only now is the circuit stable / not false triggering.

Thanks
Ernie H.

Thanks 4 all your comments, (it took a while 2 draw the circuit in LTspice) what i'm thinking is happening from a non technical viewpoint is i think its not so much the value of R1, I think the sensor when physically to close to the PIC is creating electrical noise / especially when adjusting the sensitivity to get at least 3m in distance. (the less distance more stable /closer pic can be)

Had similar thing happen with a sensor from RFrobot.

When i put some distance between the two it seems 2 work ok.

Would this be possible?

Thanks.
Ernie H.

 

My first comment is that you should be generous with decoupling capacitors - I don't see any.

Maybe some 100uf across the supply on each board, and some 100n close to the chips.