Driveway Sensor Connection

Other Hardware General Electronics
1

I have a driveway sensor receiver that lights an LED and plays a chime when a vehicle is detected. I need to trigger a relay on an arduino when this happens. I'm ok with detecting voltage and driving the relay on the arduino, but I'm having a tough time figuring out where/what to 'tap' into on the receiver.

Here are some pics:

[Album] receiver

In the first pic, the green LED is lit indicating that the chime has played through the piezo speaker. That's the condition I'm after. I'm just not sure where/what to plug into the arduino for detection.

Any thoughts?

2

Cardboard tube, black tape, and a phototransistor comes to mind.

3

Get out your trusty multimeter. My guess is that the LEDs are powered from the controller, through resistors to LED and ground.

If that is the case, you can take a signal off the LED and drive a transistor to take the Arduino input pin low.

If you don't want to hack into the board, the previous suggest is the way to do it.

Weedpharma

4

It seems that R13 goes to the green LED.
The IC side of R13 will have some logic level (5volt or 12volt).
Measure that voltage in respect to ground (lots of ground vias there) when the green LED is on or off.
You could connect that IC pin through a 10k series resistor to an Arduino digital pin.
Don't forget to join grounds.

If you can't join grounds, you will have to use an opto.
The opto LED can be driven, with a 1k current limiting resistor, from that same IC pin and ground.
Leo..

5

My reason for picking the signal from the LED is that it is a bigger pad to solder to.

Weedpharma

6

The LED will have ~1.8volt across. The IC pin (equally big) will have 5volt (or 12volt) on it.
1.8volt might not be enough to switch an Arduino pin directly.
It will be enough to power the ~1.2volt IR LED of an opto through a ~100-220ohm resistor.
Leo..

7

Wawa:
1.8volt might not be enough to switch an Arduino pin directly.

That is not "might" ... :roll_eyes:

8

That was a hint that it probably wouldn't work.
Digital "high" on a 3.3volt Arduino is ~2volt (0.6VCC in the datasheet).
Leo..

9

Wawa:
The LED will have ~1.8volt across. The IC pin (equally big) will have 5volt (or 12volt) on it.
1.8volt might not be enough to switch an Arduino pin directly.
It will be enough to power the ~1.2volt IR LED of an opto through a ~100-220ohm resistor.
Leo..

Or drive the base of a transistor to earth the Arduino pin as suggested earlier.

Weedpharma