Need help to select pull down resistor value for PIR sensor

Other Hardware General Electronics
1

I have purchased this PIR sensor below, and would like to integrate it into an arduino project I'm working on.

In the docs for it a pull-down resistor is specified, see below:

Please select an output resistor (pull-down concept) in accordance with V OUT so that the output current is maximum 100μA

Can someone specify a resistor value that will work please? 10k resistors seem to be the default for many arduino applications but I have no idea if that will work in this case.

Also, as the maximum output voltage is 0.5V, I should read this with analog input as 0.5V on a digital input won't register as high, is that correct?

2

The calculation is R = V / I
where
R is the calculated resistance, and
V is the maximum voltage, and
I is the intended current.

R = 0.5 / 100/1000000 = 5000 ohms

but the resistor may have some error in the resistance so 10000 ohms is safer. This resistor (to pull down) goes from the Arduino pin (and the PIR output) to ground.

Yes, you will have to use an analog input to measure this.

3

mattjberry:
Also, as the maximum output voltage is 0.5V...

No, it's not.
Use the sensor datasheet instead of the data sorting sheet from RS.

Datasheet states "Vdd‐0.5V", meaning HIGH output is ~4.5volt on a 5volt supply, or ~2.8volt on a 3.3volt supply.

Could be that you don't even need a pull down resistor, but use 100k (45uA) to make sure.
Leo..

4

Wawa:
No, it's not.
Use the sensor datasheet instead of the data sorting sheet from RS.

Datasheet states "Vdd‐0.5V", meaning HIGH output is ~4.5volt on a 5volt supply, or ~2.8volt on a 3.3volt supply.

Could be that you don't even need a pull down resistor, but use 100k (45uA) to make sure.
Leo..

Thank you for the clarification